chapter 3 transport layer - university of...

Computer Networking A Top Down Approach

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Thanks and enjoy JFKKWR

All material copyright 1996-2016JF Kurose and KW Ross All Rights Reserved

7th edition Jim Kurose Keith RossPearsonAddison WesleyApril 2016

Chapter 3Transport Layer

Transport Layer 2-1

Transport Layer 3-2

Chapter 3 Transport Layerour goals understand

principles behind transport layer services

bull multiplexing demultiplexing

bull reliable data transfer

bull flow controlbull congestion control

learn about Internet transport layer protocols

bull UDP connectionless transport

bull TCP connection-oriented reliable transport

bull TCP congestion control

Transport Layer 3-3

Chapter 3 outline31 transport-layer

services32 multiplexing and

demultiplexing33 connectionless

transport UDP34 principles of

reliable data transfer

35 connection-oriented transport TCPbull segment structurebull reliable data transferbull flow controlbull connection

management36 principles of

congestion control37 TCP congestion

control

Transport Layer 3-4

Transport services and protocols provide logical

communication between app processes running on different hosts

transport protocols run in end systems

bull send side breaks app messages into segments passes to network layer

bull rcv side reassembles segments into messages passes to app layer

more than one transport protocol available to apps

applicationtransportnetworkdata linkphysical


Transport Layer 3-5

Transport vs network layer network layer

logical communication between hosts transport layer

logical communication between processesbull relies on

enhances network layer services

12 kids in Annrsquos house sending letters to 12 kids in Billrsquos house

hosts = houses processes = kids app messages = letters in

envelopes transport protocol = Ann

and Bill who demux to in-house siblings

network-layer protocol = postal service

household analogy

Transport Layer 3-6

Internet transport-layer protocols reliable in-order

delivery (TCP)bull congestion control bull flow controlbull connection setup

unreliable unordered delivery UDP

bull no-frills extension of ldquobest-effortrdquo IP

services not available

bull delay guaranteesbull bandwidth guarantees



networkdata linkphysical





networkdata linkphysical network

data linkphysical

Transport Layer 3-7









control

Transport Layer 3-8

Multiplexingdemultiplexing

process

socket

use header info to deliverreceived segments to correct socket

demultiplexing at receiverhandle data from multiplesockets add transport header (later used for demultiplexing)

multiplexing at sender

transport

application

physicallink

network

P2P1

transport

application

physicallink

network

P4

transport

application

physicallink

network

P3

Transport Layer 3-9

How demultiplexing works

host receives IP datagrams

bull each datagram has source IP address destination IP address

bull each datagram carries one transport-layer segment

bull each segment has source destination port number

host uses IP addresses amp port numbers to direct segment to appropriate socket

source port dest port

32 bits

applicationdata

(payload)

other header fields

TCPUDP segment format

Transport Layer 3-10

Connectionless demultiplexing recall created socket has

host-local port DatagramSocket mySocket1 = new DatagramSocket(12534)

when host receives UDP segment

bull checks destination port in segment

bull directs UDP segment to socket with that port

recall when creating datagram to send into UDP socket must specify

bull destination IP addressbull destination port IP datagrams with same dest port but different source IP addresses andor source port numbers will be directed to same socket at dest


Connectionless demux example

DatagramSocket serverSocket = new DatagramSocket(6428)

transport

application

physicallink

network

P3transport

application

physicallink

network

P1

transport

application

physicallink

network

P4

DatagramSocket mySocket1 = new DatagramSocket (5775)

DatagramSocket mySocket2 = new DatagramSocket(9157)

source port 9157dest port 6428





Connection-oriented demux TCP socket identified

by 4-tuple bull source IP addressbull source port numberbull dest IP addressbull dest port number

demux receiver uses all four values to direct segment to appropriate socket

server host may support many simultaneous TCP sockets

bull each socket identified by its own 4-tuple

web servers have different sockets for each connecting client

bull non-persistent HTTP will have different socket for each request


Connection-oriented demux example

transport

application

physicallink

network

P3transport

application

physicallink

P4

transport

application

physicallink

network

P2

source IPport A9157dest IP port B80

source IPport B80dest IPport A9157

host IP address

A

host IP address

C

network

P6P5P3

source IPport C5775dest IPport B80


three segments all destined to IP address Bdest port 80 are demultiplexed to different sockets

server IP

address B



transport

application

physicallink

network

P3transport

application

physicallink

transport

application

physicallink

network

P2



host IP address

A

host IP address

C

server IP

address B

network

P3



P4

threaded server










control


UDP User Datagram Protocol [RFC 768] ldquono frillsrdquo ldquobare bonesrdquo

Internet transport protocol

ldquobest effortrdquo service UDP segments may be

bull lostbull delivered out-of-order

to app connectionless

bull no handshaking between UDP sender receiver

bull each UDP segment handled independently of others

UDP use streaming multimedia

apps (loss tolerant rate sensitive) DNS SNMP

reliable transfer over UDP add reliability at

application layer application-specific

error recovery


UDP segment header


32 bits

applicationdata

(payload)

UDP segment format

length checksum

length in bytes of UDP segment

including header

no connection establishment (which can add delay)

simple no connection state at sender receiver

small header size no congestion control

UDP can blast away as fast as desired

why is there a UDP


UDP checksum

sender treat segment contents

including header fields as sequence of 16-bit integers

checksum addition (onersquos complement sum) of segment contents

sender puts checksum value into UDP checksum field

receiver compute checksum of

received segment check if computed

checksum equals checksum field value

bull NO - error detectedbull YES - no error

detected But maybe errors nonethelessMore later hellip

Goal detect ldquoerrorsrdquo (eg flipped bits) in transmitted segment


Internet checksum example

example add two 16-bit integers

1 1 1 1 0 0 1 1 0 0 1 1 0 0 1 1 01 1 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1

1 1 0 1 1 1 0 1 1 1 0 1 1 1 0 1 1

1 1 0 1 1 1 0 1 1 1 0 1 1 1 1 0 01 0 1 0 0 0 1 0 0 0 1 0 0 0 0 1 1

wraparound

sumchecksum

Note when adding numbers a carryout from the most significant bit needs to be added to the result

Check out the online interactive exercises for more examples httpgaiacsumassedukurose_rossinteractive










control


Principles of reliable data transfer important in application transport link layers

bull top-10 list of important networking topics

characteristics of unreliable channel will determine complexity of reliable data transfer protocol (rdt)







important in application transport link layersbull top-10 list of important networking topics

Principles of reliable data transfer


Reliable data transfer getting started

sendside

receiveside

rdt_send() called from above (eg by app) Passed data to deliver to receiver upper layer

udt_send() called by rdtto transfer packet over

unreliable channel to receiver

rdt_rcv() called when packet arrives on rcv-side of channel

deliver_data() called by rdt to deliver data to upper


wersquoll incrementally develop sender receiver sides of

reliable data transfer protocol (rdt) consider only unidirectional data transfer

bull but control info will flow on both directions use finite state machines (FSM) to specify

sender receiver

state1

state2

event causing state transitionactions taken on state transition

state when in this ldquostaterdquo next state

uniquely determined by next event

eventactions



rdt10 reliable transfer over a reliable channel underlying channel perfectly reliable

bull no bit errorsbull no loss of packets

separate FSMs for sender receiverbull sender sends data into underlying channelbull receiver reads data from underlying channel

Wait for call from above packet = make_pkt(data)

udt_send(packet)

rdt_send(data)extract (packetdata)deliver_data(data)

Wait for call from

below

rdt_rcv(packet)

sender receiver


underlying channel may flip bits in packetbull checksum to detect bit errors

the question how to recover from errorsbull acknowledgements (ACKs) receiver explicitly tells

sender that pkt received OKbull negative acknowledgements (NAKs) receiver

explicitly tells sender that pkt had errorsbull sender retransmits pkt on receipt of NAK

new mechanisms in rdt20 (beyond rdt10)bull error detectionbull receiver feedback control msgs (ACKNAK) rcvr-

gtsender

rdt20 channel with bit errors

How do humans recover from ldquoerrorsrdquoduring conversation






new mechanisms in rdt20 (beyond rdt10)bull error detectionbull feedback control msgs (ACKNAK) from receiver to

sender



rdt20 FSM specification

Wait for call from above

sndpkt = make_pkt(data checksum)udt_send(sndpkt)

extract(rcvpktdata)deliver_data(data)udt_send(ACK)

rdt_rcv(rcvpkt) ampamp notcorrupt(rcvpkt)

rdt_rcv(rcvpkt) ampamp isACK(rcvpkt)

udt_send(sndpkt)

rdt_rcv(rcvpkt) ampampisNAK(rcvpkt)

udt_send(NAK)

rdt_rcv(rcvpkt) ampamp corrupt(rcvpkt)

Wait for ACK or

NAK

Wait for call from

belowsender

receiverrdt_send(data)


rdt20 operation with no errors


snkpkt = make_pkt(data checksum)udt_send(sndpkt)




udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)


rdt20 error scenario






udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)


rdt20 has a fatal flaw

what happens if ACKNAK corrupted

sender doesnrsquot know what happened at receiver

canrsquot just retransmit possible duplicate

handling duplicates sender retransmits

current pkt if ACKNAK corrupted

sender adds sequence number to each pkt

receiver discards (doesnrsquot deliver up) duplicate pktstop and wait

sender sends one packet then waits for receiver response


rdt21 sender handles garbled ACKNAKs

Wait for call 0 from

above

sndpkt = make_pkt(0 data checksum)udt_send(sndpkt)

rdt_send(data)

Wait for ACK or NAK 0 udt_send(sndpkt)

rdt_rcv(rcvpkt) ampamp ( corrupt(rcvpkt) ||isNAK(rcvpkt) )


rdt_send(data)

rdt_rcv(rcvpkt) ampamp notcorrupt(rcvpkt) ampamp isACK(rcvpkt)

udt_send(sndpkt)



Wait forcall 1 from

above

Wait for ACK or NAK 1


Wait for 0 from below

sndpkt = make_pkt(NAK chksum)udt_send(sndpkt)

rdt_rcv(rcvpkt) ampamp not corrupt(rcvpkt) ampamphas_seq0(rcvpkt)

rdt_rcv(rcvpkt) ampamp notcorrupt(rcvpkt) ampamp has_seq1(rcvpkt)

extract(rcvpktdata)deliver_data(data)sndpkt = make_pkt(ACK chksum)udt_send(sndpkt)




rdt_rcv(rcvpkt) ampamp (corrupt(rcvpkt)

sndpkt = make_pkt(ACK chksum)udt_send(sndpkt)





rdt21 receiver handles garbled ACKNAKs


rdt21 discussionsender seq added to pkt two seq rsquos (01)

will suffice Why must check if

received ACKNAK corrupted twice as many states

bull state must ldquorememberrdquo whether ldquoexpectedrdquo pkt should have seq of 0 or 1

receiver must check if

received packet is duplicate

bull state indicates whether 0 or 1 is expected pkt seq

note receiver can not know if its last ACKNAK received OK at sender


rdt22 a NAK-free protocol

same functionality as rdt21 using ACKs only instead of NAK receiver sends ACK for last pkt

received OKbull receiver must explicitly include seq of pkt being

ACKed duplicate ACK at sender results in same action

as NAK retransmit current pkt


rdt22 sender receiver fragments


above


rdt_send(data)

udt_send(sndpkt)

rdt_rcv(rcvpkt) ampamp ( corrupt(rcvpkt) ||

isACK(rcvpkt1) )

rdt_rcv(rcvpkt) ampamp notcorrupt(rcvpkt) ampamp isACK(rcvpkt0)

Wait for ACK

0sender FSMfragment


extract(rcvpktdata)deliver_data(data)sndpkt = make_pkt(ACK1 chksum)udt_send(sndpkt)


rdt_rcv(rcvpkt) ampamp (corrupt(rcvpkt) ||

has_seq1(rcvpkt))

udt_send(sndpkt)receiver FSM

fragment


rdt30 channels with errors and loss

new assumptionunderlying channel can also lose packets (data ACKs)

bull checksum seq ACKs retransmissions will be of help hellip but not enough

approach sender waits ldquoreasonablerdquo amount of time for ACK

retransmits if no ACK received in this time

if pkt (or ACK) just delayed (not lost)

bull retransmission will be duplicate but seq rsquos already handles this

bull receiver must specify seq of pkt being ACKed

requires countdown timer


rdt30 sendersndpkt = make_pkt(0 data checksum)udt_send(sndpkt)start_timer

rdt_send(data)

Wait for

ACK0

rdt_rcv(rcvpkt) ampamp ( corrupt(rcvpkt) ||isACK(rcvpkt1) )


above

sndpkt = make_pkt(1 data checksum)udt_send(sndpkt)start_timer

rdt_send(data)




stop_timerstop_timer

udt_send(sndpkt)start_timer

timeout


timeout

rdt_rcv(rcvpkt)

Wait for call 0from

above

Wait for

ACK1

rdt_rcv(rcvpkt)


sender receiver

rcv pkt1

rcv pkt0

send ack0

send ack1

send ack0

rcv ack0

send pkt0

send pkt1

rcv ack1

send pkt0rcv pkt0

pkt0

pkt0

pkt1

ack1

ack0

ack0

(a) no loss

sender receiver

rcv pkt1

rcv pkt0

send ack0

send ack1

send ack0

rcv ack0

send pkt0

send pkt1

rcv ack1

send pkt0rcv pkt0

pkt0

pkt0

ack1

ack0

ack0

(b) packet loss

pkt1X

loss

pkt1timeout

resend pkt1

rdt30 in action


rdt30 in action

rcv pkt1send ack1

(detect duplicate)

pkt1

sender receiver

rcv pkt1

rcv pkt0

send ack0

send ack1

send ack0

rcv ack0

send pkt0

send pkt1

rcv ack1

send pkt0rcv pkt0

pkt0

pkt0

ack1

ack0

ack0

(c) ACK loss

ack1X

loss

pkt1timeout

resend pkt1

rcv pkt1send ack1

(detect duplicate)

pkt1

sender receiver

rcv pkt1

send ack0rcv ack0

send pkt1

send pkt0rcv pkt0

pkt0

ack0

(d) premature timeout delayed ACK

pkt1timeout

resend pkt1

ack1

send ack1

send pkt0rcv ack1

pkt0

ack1

ack0

send pkt0rcv ack1 pkt0

rcv pkt0send ack0ack0

rcv pkt0send ack0(detect duplicate)


Performance of rdt30 rdt30 is correct but performance stinks eg 1 Gbps link 15 ms prop delay 8000 bit

packet

U sender utilization ndash fraction of time sender busy sending

U sender =

008 30008

= 000027 L R RTT + L R

=

if RTT=30 msec 1KB pkt every 30 msec 33kBsec thruput over 1 Gbps link

network protocol limits use of physical resources

Dtrans = LR

8000 bits109 bitssec= = 8 microsecs


rdt30 stop-and-wait operation

first packet bit transmitted t = 0

sender receiver

RTT

last packet bit transmitted t = L R

first packet bit arriveslast packet bit arrives send ACK

ACK arrives send next packet t = RTT + L R

U sender =

008 30008

= 000027 L R RTT + L R

=


Pipelined protocolspipelining sender allows multiple ldquoin-flightrdquo

yet-to-be-acknowledged pktsbull range of sequence numbers must be increasedbull buffering at sender andor receiver

two generic forms of pipelined protocols go-Back-N selective repeat


Pipelining increased utilization

first packet bit transmitted t = 0sender receiver

RTT

last bit transmitted t = L R



last bit of 2nd packet arrives send ACKlast bit of 3rd packet arrives send ACK

3-packet pipelining increasesutilization by a factor of 3

U sender =

0024 30008

= 000081 3L R RTT + L R

=


Pipelined protocols overviewGo-back-N sender can have up

to N unacked packets in pipeline receiver only sends

cumulative ackbull doesnrsquot ack packet if

therersquos a gap sender has timer for

oldest unacked packet

bull when timer expires retransmit all unacked packets

Selective Repeat sender can have up to

N unackrsquoed packets in pipeline rcvr sends individual

ack for each packet

sender maintains timer for each unacked packet

bull when timer expires retransmit only that unacked packet


Go-Back-N sender k-bit seq in pkt header ldquowindowrdquo of up to N consecutive unackrsquoed pkts allowed

ACK(n) ACKs all pkts up to including seq n -ldquocumulative ACKrdquobull may receive duplicate ACKs (see receiver)

timer for oldest in-flight pkt timeout(n) retransmit packet n and all higher seq pkts in

window


GBN sender extended FSM

Wait start_timerudt_send(sndpkt[base])udt_send(sndpkt[base+1])hellipudt_send(sndpkt[nextseqnum-1])

timeout

rdt_send(data)

if (nextseqnum lt base+N) sndpkt[nextseqnum] = make_pkt(nextseqnumdatachksum)udt_send(sndpkt[nextseqnum])if (base == nextseqnum)

start_timernextseqnum++

elserefuse_data(data)

base = getacknum(rcvpkt)+1If (base == nextseqnum)

stop_timerelsestart_timer


base=1nextseqnum=1



ACK-only always send ACK for correctly-received pkt with highest in-order seq

bull may generate duplicate ACKsbull need only remember expectedseqnum

out-of-order pkt bull discard (donrsquot buffer) no receiver bufferingbull re-ACK pkt with highest in-order seq

Wait

udt_send(sndpkt)default

rdt_rcv(rcvpkt)ampamp notcurrupt(rcvpkt)ampamp hasseqnum(rcvpktexpectedseqnum)

extract(rcvpktdata)deliver_data(data)sndpkt = make_pkt(expectedseqnumACKchksum)udt_send(sndpkt)expectedseqnum++

expectedseqnum=1sndpkt = make_pkt(expectedseqnumACKchksum)

GBN receiver extended FSM


GBN in action

send pkt0send pkt1send pkt2send pkt3

(wait)

sender receiver

receive pkt0 send ack0receive pkt1 send ack1

receive pkt3 discard (re)send ack1rcv ack0 send pkt4

rcv ack1 send pkt5

pkt 2 timeoutsend pkt2send pkt3send pkt4send pkt5

Xloss

receive pkt4 discard (re)send ack1


rcv pkt2 deliver send ack2rcv pkt3 deliver send ack3rcv pkt4 deliver send ack4rcv pkt5 deliver send ack5

ignore duplicate ACK

0 1 2 3 4 5 6 7 8

sender window (N=4)

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8


Selective repeat receiver individually acknowledges all

correctly received pktsbull buffers pkts as needed for eventual in-order

delivery to upper layer sender only resends pkts for which ACK not

receivedbull sender timer for each unACKed pkt

sender windowbull N consecutive seq rsquosbull limits seq s of sent unACKed pkts


Selective repeat sender receiver windows


Selective repeat

data from above if next available seq in

window send pkttimeout(n) resend pkt n restart

timerACK(n) in

[sendbasesendbase+N] mark pkt n as received if n smallest unACKed

pkt advance window base to next unACKed seq

senderpkt n in [rcvbase rcvbase+N-1]

send ACK(n) out-of-order buffer in-order deliver (also

deliver buffered in-order pkts) advance window to next not-yet-received pkt

pkt n in [rcvbase-Nrcvbase-1]

ACK(n)otherwise ignore

receiver


Selective repeat in action


(wait)

sender receiver


receive pkt3 buffer send ack3rcv ack0 send pkt4

rcv ack1 send pkt5

pkt 2 timeoutsend pkt2

Xloss

receive pkt4 buffer send ack4


rcv pkt2 deliver pkt2pkt3 pkt4 pkt5 send ack2

record ack3 arrived

0 1 2 3 4 5 6 7 8

sender window (N=4)

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

record ack4 arrivedrecord ack5 arrived

Q what happens when ack2 arrives


Selective repeatdilemmaexample seq rsquos 0 1 2 3 window size=3

receiver window(after receipt)

sender window(after receipt)

0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2

pkt0pkt1pkt2

0 1 2 3 0 1 2 pkt0

timeoutretransmit pkt0

0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2XXX

will accept packetwith seq number 0(b) oops

0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2

pkt0pkt1pkt2

0 1 2 3 0 1 2pkt0

0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2

Xwill accept packetwith seq number 0

0 1 2 3 0 1 2 pkt3

(a) no problem

receiver canrsquot see sender sidereceiver behavior identical in both cases

somethingrsquos (very) wrong

receiver sees no difference in two scenarios

duplicate data accepted as new in (b)

Q what relationship between seq size and window size to avoid problem in (b)










control


TCP Overview RFCs 79311221323 2018 2581

full duplex databull bi-directional data

flow in same connection

bull MSS maximum segment size

connection-orientedbull handshaking

(exchange of control msgs) inits sender receiver state before data exchange

flow controlledbull sender will not

overwhelm receiver

point-to-pointbull one sender one

receiver reliable in-order byte

steambull no ldquomessage

boundariesrdquo pipelined

bull TCP congestion and flow control set window size


TCP segment structure


32 bits

applicationdata

(variable length)

sequence numberacknowledgement number

receive window

Urg data pointerchecksumFSRPAUhead

lennot

used

options (variable length)

URG urgent data (generally not used)

ACK ACK valid

PSH push data now(generally not used)

RST SYN FINconnection estab(setup teardown

commands)

bytes rcvr willingto accept

countingby bytes of data(not segments)

Internetchecksum

(as in UDP)


TCP seq numbers ACKssequence numbers

bull byte stream ldquonumberrdquoof first byte in segmentrsquos data

acknowledgementsbull seq of next byte expected from other side

bull cumulative ACKQ how receiver handles out-of-order segmentsbull A TCP spec doesnrsquot say - up to implementor



checksum

rwndurg pointer

incoming segment to sender

A

sent ACKed

sent not-yet ACKed(ldquoin-flightrdquo)

usablebut not yet sent

not usable

window sizeN

sender sequence number space



checksum

rwndurg pointer

outgoing segment from sender


TCP seq numbers ACKs

UsertypeslsquoCrsquo

host ACKsreceipt

of echoedlsquoCrsquo

host ACKsreceipt oflsquoCrsquo echoesback lsquoCrsquo

simple telnet scenario

Host BHost A

Seq=42 ACK=79 data = lsquoCrsquo


Seq=43 ACK=80


TCP round trip time timeoutQ how to set TCP

timeout value longer than RTT

bull but RTT varies too short premature

timeout unnecessary retransmissions too long slow

reaction to segment loss

Q how to estimate RTT

SampleRTT measured time from segment transmission until ACK receipt

bull ignore retransmissions SampleRTT will vary

want estimated RTT ldquosmootherrdquo

bull average several recentmeasurements not just current SampleRTT


RTT gaiacsumassedu to fantasiaeurecomfr

100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106time (seconnds)

RTT

(mill

iseco

nds)

SampleRTT Estimated RTT

EstimatedRTT = (1- )EstimatedRTT + SampleRTT

exponential weighted moving average influence of past sample decreases

exponentially fast typical value = 0125

TCP round trip time timeoutRT

T (m

illise

cond

s)


sampleRTTEstimatedRTT

time (seconds)


timeout interval EstimatedRTT plus ldquosafety marginrdquo

bull large variation in EstimatedRTT -gt larger safety margin

estimate SampleRTT deviation from EstimatedRTT DevRTT = (1-)DevRTT +|SampleRTT-EstimatedRTT|

TCP round trip time timeout

(typically = 025)

TimeoutInterval = EstimatedRTT + 4DevRTT

estimated RTT ldquosafety marginrdquo











control


TCP reliable data transfer TCP creates rdt

service on top of IPrsquos unreliable service

bull pipelined segmentsbull cumulative acksbull single retransmission

timer retransmissions

triggered bybull timeout eventsbull duplicate acks

letrsquos initially consider simplified TCP sender

bull ignore duplicate acksbull ignore flow control

congestion control


TCP sender eventsdata rcvd from app create segment with

seq seq is byte-stream

number of first data byte in segment start timer if not

already running bull think of timer as for

oldest unacked segment

bull expiration interval TimeOutInterval

timeout retransmit segment

that caused timeout restart timerack rcvd if ack acknowledges

previously unacked segments

bull update what is known to be ACKed

bull start timer if there are still unacked segments


TCP sender (simplified)

waitfor

event

NextSeqNum = InitialSeqNumSendBase = InitialSeqNum

create segment seq NextSeqNumpass segment to IP (ie ldquosendrdquo)NextSeqNum = NextSeqNum + length(data) if (timer currently not running)

start timer

data received from application above

retransmit not-yet-acked segment with smallest seq

start timer

timeout

if (y gt SendBase) SendBase = y SendBasendash1 last cumulatively ACKed byte if (there are currently not-yet-acked segments)

start timerelse stop timer

ACK received with ACK field value y


TCP retransmission scenarios

lost ACK scenario

Host BHost A

Seq=92 8 bytes of data

ACK=100


Xtimeo

ut

ACK=100

premature timeout

Host BHost A


ACK=100

Seq=92 8bytes of data

timeo

ut

ACK=120


ACK=120

SendBase=100

SendBase=120

SendBase=120

SendBase=92



X

cumulative ACK

Host BHost A


ACK=100


timeo

ut


ACK=120


TCP ACK generation [RFC 1122 RFC 2581]

event at receiver

arrival of in-order segment withexpected seq All data up toexpected seq already ACKed

arrival of in-order segment withexpected seq One other segment has ACK pending

arrival of out-of-order segmenthigher-than-expect seq Gap detected

arrival of segment that partially or completely fills gap

TCP receiver action

delayed ACK Wait up to 500msfor next segment If no next segmentsend ACK

immediately send single cumulative ACK ACKing both in-order segments

immediately send duplicate ACKindicating seq of next expected byte

immediate send ACK provided thatsegment starts at lower end of gap


TCP fast retransmit time-out period

often relatively longbull long delay before

resending lost packet detect lost segments

via duplicate ACKsbull sender often sends

many segments back-to-back

bull if segment is lost there will likely be many duplicate ACKs

if sender receives 3 ACKs for same data(ldquotriple duplicate ACKsrdquo) resend unacked segment with smallest seq likely that unacked

segment lost so donrsquot wait for timeout

TCP fast retransmit

(ldquotriple duplicate ACKsrdquo)


X

fast retransmit after sender receipt of triple duplicate ACK

Host BHost A


ACK=100

timeo

ut ACK=100

ACK=100ACK=100

TCP fast retransmit












control


TCP flow controlapplication

process

TCP socketreceiver buffers

TCPcode

IPcode

applicationOS

receiver protocol stack

application may remove data from

TCP socket buffers hellip

hellip slower than TCP receiver is delivering(sender is sending)

from sender

receiver controls sender so sender wonrsquot overflow receiverrsquos buffer by transmitting too much too fast

flow control


TCP flow control

buffered data

free buffer spacerwnd

RcvBuffer

TCP segment payloads

to application process receiver ldquoadvertisesrdquo free

buffer space by including rwnd value in TCP header of receiver-to-sender segments

bull RcvBuffer size set via socket options (typical default is 4096 bytes)

bull many operating systems autoadjust RcvBuffer

sender limits amount of unacked (ldquoin-flightrdquo) data to receiverrsquos rwnd value

guarantees receive buffer will not overflow

receiver-side buffering










control


Connection Managementbefore exchanging data senderreceiver ldquohandshakerdquo

agree to establish connection (each knowing the other willing to establish connection)

agree on connection parameters

connection state ESTABconnection variables

seq client-to-serverserver-to-client

rcvBuffer sizeat serverclient

application

network

connection state ESTABconnection Variables



application

network

Socket clientSocket = newSocket(hostnameport number)

Socket connectionSocket = welcomeSocketaccept()


Q will 2-way handshake always work in network

variable delays retransmitted messages

(eg req_conn(x)) due to message loss

message reordering canrsquot ldquoseerdquo other side

2-way handshake

Letrsquos talk

OKESTAB

ESTAB

choose x req_conn(x)ESTAB

ESTABacc_conn(x)

Agreeing to establish a connection


Agreeing to establish a connection2-way handshake failure scenarios

retransmitreq_conn(x)

ESTAB

req_conn(x)

half open connection(no client)

client terminates

serverforgets x

connection x completes


ESTAB

req_conn(x)

data(x+1)

retransmitdata(x+1)

acceptdata(x+1)

choose xreq_conn(x)

ESTAB

ESTAB

acc_conn(x)

client terminates

ESTAB

choose xreq_conn(x)

ESTABacc_conn(x)

data(x+1) acceptdata(x+1)

connection x completes server

forgets x


TCP 3-way handshake

SYNbit=1 Seq=x

choose init seq num xsend TCP SYN msg

ESTAB

SYNbit=1 Seq=yACKbit=1 ACKnum=x+1

choose init seq num ysend TCP SYNACKmsg acking SYN

ACKbit=1 ACKnum=y+1

received SYNACK(x) indicates server is livesend ACK for SYNACK

this segment may contain client-to-server data received ACK(y)

indicates client is live

SYNSENT

ESTAB

SYN RCVD

client stateLISTEN

server stateLISTEN


TCP 3-way handshake FSM

closed

listen

SYNrcvd

SYNsent

ESTAB


SYN(seq=x)


SYN(x)SYNACK(seq=yACKnum=x+1)

create new socket for communication back to client

SYNACK(seq=yACKnum=x+1)ACK(ACKnum=y+1)ACK(ACKnum=y+1)


TCP closing a connection client server each close their side of

connectionbull send TCP segment with FIN bit = 1

respond to received FIN with ACKbull on receiving FIN ACK can be combined with own

FIN simultaneous FIN exchanges can be handled


FIN_WAIT_2

CLOSE_WAIT

FINbit=1 seq=y

ACKbit=1 ACKnum=y+1

ACKbit=1 ACKnum=x+1wait for server

close

can stillsend data

can no longersend data

LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2max

segment lifetime

CLOSED

TCP closing a connection

FIN_WAIT_1 FINbit=1 seq=xcan no longersend but canreceive data

clientSocketclose()

client state server stateESTABESTAB










control


congestion informally ldquotoo many sources sending too

much data too fast for network to handlerdquo different from flow control manifestations

bull lost packets (buffer overflow at routers)bull long delays (queueing in router buffers)

a top-10 problem

Principles of congestion control


Causescosts of congestion scenario 1 two senders two

receivers one router infinite

buffers output link capacity R no retransmission

maximum per-connection throughput R2

unlimited shared output link buffers

Host A

original data in

Host B

throughput out

R2

R2

out

in R2de

lay

in large delays as arrival rate

in approaches capacity


one router finite buffers sender retransmission of timed-out packet

bull application-layer input = application-layer output in = out

bull transport-layer input includes retransmissions in in

finite shared output link buffers

Host A

in original data

Host B

outin original data plusretransmitted data

lsquo

Causescosts of congestion scenario 2


idealization perfect knowledge

sender sends only when router buffers available


in original dataoutin original data plus

retransmitted datacopy

free buffer space

R2

R2

out

in


Host B

A




no buffer space

Idealization known loss packets can be lost dropped at router due to full buffers

sender only resends if packet known to be lost


A

Host B



retransmitted data

free buffer space




R2

R2in

out

when sending at R2 some packets are retransmissions but asymptotic goodput is still R2 (why)

A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out

when sending at R2 some packets are retransmissions including duplicated that are delivered

Host B

Realistic duplicates packets can be lost

dropped at router due to full buffers

sender times out prematurely sending twocopies both of which are delivered



R2

out


ldquocostsrdquo of congestion more work (retrans) for given ldquogoodputrdquo unneeded retransmissions link carries multiple copies

of pktbull decreasing goodput

R2in

Causescosts of congestion scenario 2Realistic duplicates packets can be lost




four senders multihop paths timeoutretransmit

Q what happens as in and in

rsquo increase


Host A out


Host B

Host CHost D

in original datain original data plus

retransmitted data

A as red inrsquo increases all

arriving blue pkts at upper queue are dropped blue throughput 0


another ldquocostrdquo of congestion when packet dropped any ldquoupstream

transmission capacity used for that packet was wasted


C2

C2

out

inrsquo










control


TCP congestion control additive increase multiplicative decrease

approach sender increases transmission rate (window size) probing for usable bandwidth until loss occursbull additive increase increase cwnd by 1 MSS

every RTT until loss detectedbull multiplicative decrease cut cwnd in half after

loss

cwnd

TCP

send

er

cong

estio

n w

indo

w s

ize

AIMD saw toothbehavior probing

for bandwidth

additively increase window size helliphellip until loss occurs (then cut window in half)

time


TCP Congestion Control details

sender limits transmission

cwnd is dynamic function of perceived network congestion

TCP sending rate roughly send cwnd

bytes wait RTT for ACKS then send more bytes

last byteACKed sent not-

yet ACKed(ldquoin-flightrdquo)

last byte sent

cwnd

LastByteSent-LastByteAcked

lt cwnd


rate ~~cwndRTT

bytessec


TCP Slow Start when connection

begins increase rate exponentially until first loss event

bull initially cwnd = 1 MSSbull double cwnd every RTTbull done by incrementing cwnd for every ACK received

summary initial rate is slow but ramps up exponentially fast

Host A

RTT

Host B

time


TCP detecting reacting to loss loss indicated by timeout

bull cwnd set to 1 MSS bull window then grows exponentially (as in slow

start) to threshold then grows linearly loss indicated by 3 duplicate ACKs TCP

RENObull dup ACKs indicate network capable of

delivering some segments bull cwnd is cut in half window then grows linearly

TCP Tahoe always sets cwnd to 1 (timeout or 3 duplicate acks)


Q when should the exponential increase switch to linear

A when cwnd gets to 12 of its value before timeout

Implementation variable ssthresh on loss event ssthresh is set to 12 of cwnd just before loss event

TCP switching from slow start to CA



Summary TCP Congestion Control

timeoutssthresh = cwnd2

cwnd = 1 MSSdupACKcount = 0

retransmit missing segment

cwnd gt ssthresh

congestionavoidance

cwnd = cwnd + MSS (MSScwnd)dupACKcount = 0

transmit new segment(s) as allowed

new ACK

dupACKcount++duplicate ACK

fastrecovery

cwnd = cwnd + MSStransmit new segment(s) as allowed

duplicate ACK

ssthresh= cwnd2cwnd = ssthresh + 3


dupACKcount == 3

timeoutssthresh = cwnd2cwnd = 1 dupACKcount = 0retransmit missing segment

ssthresh= cwnd2cwnd = ssthresh + 3retransmit missing segment

dupACKcount == 3cwnd = ssthreshdupACKcount = 0

New ACK

slow start




cwnd = cwnd+MSSdupACKcount = 0transmit new segment(s) as allowed

new ACKdupACKcount++duplicate ACK

cwnd = 1 MSS

ssthresh = 64 KBdupACKcount = 0

NewACK

NewACK

NewACK


TCP throughput avg TCP thruput as function of window size

RTTbull ignore slow start assume always data to send

W window size (measured in bytes) where loss occursbull avg window size ( in-flight bytes) is frac34 Wbull avg thruput is 34W per RTT

W

W2

avg TCP thruput = 34

WRTT bytessec


TCP Futures TCP over ldquolong fat pipesrdquo example 1500 byte segments 100ms RTT

want 10 Gbps throughput requires W = 83333 in-flight segments throughput in terms of segment loss

probability L [Mathis 1997]

to achieve 10 Gbps throughput need a loss rate of L = 210-10 ndash a very small loss rate

new versions of TCP for high-speed

TCP throughput = 122 MSSRTT L


fairness goal if K TCP sessions share same bottleneck link of bandwidth R each should have average rate of RK

TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2


Why is TCP fairtwo competing sessions additive increase gives slope of 1 as throughout

increases multiplicative decrease decreases throughput

proportionally R

R

equal bandwidth share

Connection 1 throughput

congestion avoidance additive increaseloss decrease window by factor of 2



Fairness (more)Fairness and UDP multimedia apps

often do not use TCP

bull do not want rate throttled by congestion control

instead use UDPbull send audiovideo at

constant rate tolerate packet loss

Fairness parallel TCP connections application can open

multiple parallel connections between two hosts web browsers do this eg link of rate R with

9 existing connections

bull new app asks for 1 TCP gets rate R10

bull new app asks for 11 TCPs gets R2


network-assisted congestion control two bits in IP header (ToS field) marked by network

router to indicate congestion congestion indication carried to receiving host receiver (seeing congestion indication in IP

datagram) ) sets ECE bit on receiver-to-sender ACK segment to notify sender of congestion

Explicit Congestion Notification (ECN)

sourceapplicationtransportnetwork

linkphysical

destinationapplicationtransportnetwork

linkphysical

ECN=00 ECN=11

ECE=1

IP datagram

TCP ACK segment


Chapter 3 summary principles behind

transport layer servicesbull multiplexing

demultiplexingbull reliable data transferbull flow controlbull congestion control

instantiation implementation in the Internet

bull UDPbull TCP

next leaving the

network ldquoedgerdquo(application transport layers) into the network ldquocorerdquo two network layer

chaptersbull data planebull control plane

Transport Layer 3-2

Chapter 3 Transport Layerour goals understand

principles behind transport layer services

bull multiplexing demultiplexing

bull reliable data transfer

bull flow controlbull congestion control

learn about Internet transport layer protocols

bull UDP connectionless transport

bull TCP connection-oriented reliable transport

bull TCP congestion control

Transport Layer 3-3









control

Transport Layer 3-4









Transport Layer 3-5










household analogy

Transport Layer 3-6















data linkphysical

Transport Layer 3-7









control

Transport Layer 3-8


process

socket




transport

application

physicallink

network

P2P1

transport

application

physicallink

network

P4

transport

application

physicallink

network

P3

Transport Layer 3-9








32 bits

applicationdata

(payload)

other header fields













transport

application

physicallink

network

P3transport

application

physicallink

network

P1

transport

application

physicallink

network

P4

















transport

application

physicallink

network

P3transport

application

physicallink

P4

transport

application

physicallink

network

P2



host IP address

A

host IP address

C

network

P6P5P3




server IP

address B



transport

application

physicallink

network

P3transport

application

physicallink

transport

application

physicallink

network

P2



host IP address

A

host IP address

C

server IP

address B

network

P3



P4

threaded server










control













error recovery


UDP segment header


32 bits

applicationdata

(payload)

UDP segment format

length checksum


including header





why is there a UDP


UDP checksum














1 1 1 1 0 0 1 1 0 0 1 1 0 0 1 1 01 1 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1

1 1 0 1 1 1 0 1 1 1 0 1 1 1 0 1 1

1 1 0 1 1 1 0 1 1 1 0 1 1 1 1 0 01 0 1 0 0 0 1 0 0 0 1 0 0 0 0 1 1

wraparound

sumchecksum












control















sendside

receiveside










sender receiver

state1

state2




eventactions







udt_send(packet)


Wait for call from

below

rdt_rcv(packet)

sender receiver







gtsender









sender









udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

belowsender









udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)








udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)














above


rdt_send(data)




rdt_send(data)


udt_send(sndpkt)



Wait forcall 1 from

above




































above


rdt_send(data)

udt_send(sndpkt)


isACK(rcvpkt1) )


Wait for ACK

0sender FSMfragment





has_seq1(rcvpkt))


fragment













rdt_send(data)

Wait for

ACK0



above


rdt_send(data)






timeout


timeout

rdt_rcv(rcvpkt)

Wait for call 0from

above

Wait for

ACK1

rdt_rcv(rcvpkt)


sender receiver

rcv pkt1

rcv pkt0

send ack0

send ack1

send ack0

rcv ack0

send pkt0

send pkt1

rcv ack1

send pkt0rcv pkt0

pkt0

pkt0

pkt1

ack1

ack0

ack0

(a) no loss

sender receiver

rcv pkt1

rcv pkt0

send ack0

send ack1

send ack0

rcv ack0

send pkt0

send pkt1

rcv ack1

send pkt0rcv pkt0

pkt0

pkt0

ack1

ack0

ack0

(b) packet loss

pkt1X

loss

pkt1timeout

resend pkt1

rdt30 in action


rdt30 in action

rcv pkt1send ack1

(detect duplicate)

pkt1

sender receiver

rcv pkt1

rcv pkt0

send ack0

send ack1

send ack0

rcv ack0

send pkt0

send pkt1

rcv ack1

send pkt0rcv pkt0

pkt0

pkt0

ack1

ack0

ack0

(c) ACK loss

ack1X

loss

pkt1timeout

resend pkt1

rcv pkt1send ack1

(detect duplicate)

pkt1

sender receiver

rcv pkt1

send ack0rcv ack0

send pkt1

send pkt0rcv pkt0

pkt0

ack0


pkt1timeout

resend pkt1

ack1

send ack1

send pkt0rcv ack1

pkt0

ack1

ack0






packet


U sender =

008 30008

= 000027 L R RTT + L R

=



Dtrans = LR





sender receiver

RTT




U sender =

008 30008

= 000027 L R RTT + L R

=








RTT






U sender =

0024 30008

= 000081 3L R RTT + L R

=










ack for each packet







window




timeout

rdt_send(data)







base=1nextseqnum=1






Wait







GBN in action


(wait)

sender receiver



rcv ack1 send pkt5


Xloss





0 1 2 3 4 5 6 7 8

sender window (N=4)

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8










Selective repeat



timerACK(n) in








receiver




(wait)

sender receiver



rcv ack1 send pkt5


Xloss




record ack3 arrived

0 1 2 3 4 5 6 7 8

sender window (N=4)

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8







0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2

pkt0pkt1pkt2

0 1 2 3 0 1 2 pkt0


0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2XXX


0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2

pkt0pkt1pkt2

0 1 2 3 0 1 2pkt0

0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2


0 1 2 3 0 1 2 pkt3

(a) no problem















control









overwhelm receiver









32 bits

applicationdata

(variable length)


receive window


lennot

used



ACK ACK valid



commands)



Internetchecksum

(as in UDP)








checksum

rwndurg pointer


A

sent ACKed



not usable

window sizeN




checksum

rwndurg pointer





host ACKsreceipt




Host BHost A



Seq=43 ACK=80














100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106time (seconnds)

RTT

(mill

iseco

nds)






T (m

illise

cond

s)



time (seconds)






(typically = 025)













control









congestion control















waitfor

event



start timer



start timer

timeout






lost ACK scenario

Host BHost A


ACK=100


Xtimeo

ut

ACK=100

premature timeout

Host BHost A


ACK=100


timeo

ut

ACK=120


ACK=120

SendBase=100

SendBase=120

SendBase=120

SendBase=92



X

cumulative ACK

Host BHost A


ACK=100


timeo

ut


ACK=120



event at receiver





TCP receiver action














TCP fast retransmit



X


Host BHost A


ACK=100

timeo

ut ACK=100

ACK=100ACK=100

TCP fast retransmit












control



process


TCPcode

IPcode

applicationOS





from sender


flow control


TCP flow control

buffered data


RcvBuffer


















control








application

network




application

network








2-way handshake

Letrsquos talk

OKESTAB

ESTAB


ESTABacc_conn(x)





ESTAB

req_conn(x)


client terminates

serverforgets x



ESTAB

req_conn(x)

data(x+1)

retransmitdata(x+1)

acceptdata(x+1)

choose xreq_conn(x)

ESTAB

ESTAB

acc_conn(x)

client terminates

ESTAB

choose xreq_conn(x)

ESTABacc_conn(x)



forgets x


TCP 3-way handshake

SYNbit=1 Seq=x


ESTAB



ACKbit=1 ACKnum=y+1




SYNSENT

ESTAB

SYN RCVD

client stateLISTEN

server stateLISTEN



closed

listen

SYNrcvd

SYNsent

ESTAB


SYN(seq=x)











FIN_WAIT_2

CLOSE_WAIT

FINbit=1 seq=y

ACKbit=1 ACKnum=y+1


close

can stillsend data


LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2max

segment lifetime

CLOSED



clientSocketclose()











control





a top-10 problem








Host A

original data in

Host B

throughput out

R2

R2

out

in R2de

lay








Host A

in original data

Host B


lsquo








free buffer space

R2

R2

out

in


Host B

A




no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







rsquo increase


Host A out


Host B

Host CHost D


retransmitted data







C2

C2

out

inrsquo










control





loss

cwnd

TCP

send

er

cong

estio

n w

indo

w s

ize


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwndRTT

bytessec






Host A

RTT

Host B

time



















cwnd gt ssthresh

congestionavoidance



new ACK


fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


WRTT bytessec










TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R






















linkphysical


linkphysical

ECN=00 ECN=11

ECE=1

IP datagram

TCP ACK segment






bull UDPbull TCP

next leaving the



Transport Layer 3-3









control

Transport Layer 3-4









Transport Layer 3-5










household analogy

Transport Layer 3-6















data linkphysical

Transport Layer 3-7









control

Transport Layer 3-8


process

socket




transport

application

physicallink

network

P2P1

transport

application

physicallink

network

P4

transport

application

physicallink

network

P3

Transport Layer 3-9








32 bits

applicationdata

(payload)

other header fields













transport

application

physicallink

network

P3transport

application

physicallink

network

P1

transport

application

physicallink

network

P4

















transport

application

physicallink

network

P3transport

application

physicallink

P4

transport

application

physicallink

network

P2



host IP address

A

host IP address

C

network

P6P5P3




server IP

address B



transport

application

physicallink

network

P3transport

application

physicallink

transport

application

physicallink

network

P2



host IP address

A

host IP address

C

server IP

address B

network

P3



P4

threaded server










control













error recovery


UDP segment header


32 bits

applicationdata

(payload)

UDP segment format

length checksum


including header





why is there a UDP


UDP checksum














1 1 1 1 0 0 1 1 0 0 1 1 0 0 1 1 01 1 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1

1 1 0 1 1 1 0 1 1 1 0 1 1 1 0 1 1

1 1 0 1 1 1 0 1 1 1 0 1 1 1 1 0 01 0 1 0 0 0 1 0 0 0 1 0 0 0 0 1 1

wraparound

sumchecksum












control















sendside

receiveside










sender receiver

state1

state2




eventactions







udt_send(packet)


Wait for call from

below

rdt_rcv(packet)

sender receiver







gtsender









sender









udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

belowsender









udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)








udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)














above


rdt_send(data)




rdt_send(data)


udt_send(sndpkt)



Wait forcall 1 from

above




































above


rdt_send(data)

udt_send(sndpkt)


isACK(rcvpkt1) )


Wait for ACK

0sender FSMfragment





has_seq1(rcvpkt))


fragment













rdt_send(data)

Wait for

ACK0



above


rdt_send(data)






timeout


timeout

rdt_rcv(rcvpkt)

Wait for call 0from

above

Wait for

ACK1

rdt_rcv(rcvpkt)


sender receiver

rcv pkt1

rcv pkt0

send ack0

send ack1

send ack0

rcv ack0

send pkt0

send pkt1

rcv ack1

send pkt0rcv pkt0

pkt0

pkt0

pkt1

ack1

ack0

ack0

(a) no loss

sender receiver

rcv pkt1

rcv pkt0

send ack0

send ack1

send ack0

rcv ack0

send pkt0

send pkt1

rcv ack1

send pkt0rcv pkt0

pkt0

pkt0

ack1

ack0

ack0

(b) packet loss

pkt1X

loss

pkt1timeout

resend pkt1

rdt30 in action


rdt30 in action

rcv pkt1send ack1

(detect duplicate)

pkt1

sender receiver

rcv pkt1

rcv pkt0

send ack0

send ack1

send ack0

rcv ack0

send pkt0

send pkt1

rcv ack1

send pkt0rcv pkt0

pkt0

pkt0

ack1

ack0

ack0

(c) ACK loss

ack1X

loss

pkt1timeout

resend pkt1

rcv pkt1send ack1

(detect duplicate)

pkt1

sender receiver

rcv pkt1

send ack0rcv ack0

send pkt1

send pkt0rcv pkt0

pkt0

ack0


pkt1timeout

resend pkt1

ack1

send ack1

send pkt0rcv ack1

pkt0

ack1

ack0






packet


U sender =

008 30008

= 000027 L R RTT + L R

=



Dtrans = LR





sender receiver

RTT




U sender =

008 30008

= 000027 L R RTT + L R

=








RTT






U sender =

0024 30008

= 000081 3L R RTT + L R

=










ack for each packet







window




timeout

rdt_send(data)







base=1nextseqnum=1






Wait







GBN in action


(wait)

sender receiver



rcv ack1 send pkt5


Xloss





0 1 2 3 4 5 6 7 8

sender window (N=4)

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8










Selective repeat



timerACK(n) in








receiver




(wait)

sender receiver



rcv ack1 send pkt5


Xloss




record ack3 arrived

0 1 2 3 4 5 6 7 8

sender window (N=4)

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8







0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2

pkt0pkt1pkt2

0 1 2 3 0 1 2 pkt0


0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2XXX


0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2

pkt0pkt1pkt2

0 1 2 3 0 1 2pkt0

0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2


0 1 2 3 0 1 2 pkt3

(a) no problem















control









overwhelm receiver









32 bits

applicationdata

(variable length)


receive window


lennot

used



ACK ACK valid



commands)



Internetchecksum

(as in UDP)








checksum

rwndurg pointer


A

sent ACKed



not usable

window sizeN




checksum

rwndurg pointer





host ACKsreceipt




Host BHost A



Seq=43 ACK=80














100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106time (seconnds)

RTT

(mill

iseco

nds)






T (m

illise

cond

s)



time (seconds)






(typically = 025)













control









congestion control















waitfor

event



start timer



start timer

timeout






lost ACK scenario

Host BHost A


ACK=100


Xtimeo

ut

ACK=100

premature timeout

Host BHost A


ACK=100


timeo

ut

ACK=120


ACK=120

SendBase=100

SendBase=120

SendBase=120

SendBase=92



X

cumulative ACK

Host BHost A


ACK=100


timeo

ut


ACK=120



event at receiver





TCP receiver action














TCP fast retransmit



X


Host BHost A


ACK=100

timeo

ut ACK=100

ACK=100ACK=100

TCP fast retransmit












control



process


TCPcode

IPcode

applicationOS





from sender


flow control


TCP flow control

buffered data


RcvBuffer


















control








application

network




application

network








2-way handshake

Letrsquos talk

OKESTAB

ESTAB


ESTABacc_conn(x)





ESTAB

req_conn(x)


client terminates

serverforgets x



ESTAB

req_conn(x)

data(x+1)

retransmitdata(x+1)

acceptdata(x+1)

choose xreq_conn(x)

ESTAB

ESTAB

acc_conn(x)

client terminates

ESTAB

choose xreq_conn(x)

ESTABacc_conn(x)



forgets x


TCP 3-way handshake

SYNbit=1 Seq=x


ESTAB



ACKbit=1 ACKnum=y+1




SYNSENT

ESTAB

SYN RCVD

client stateLISTEN

server stateLISTEN



closed

listen

SYNrcvd

SYNsent

ESTAB


SYN(seq=x)











FIN_WAIT_2

CLOSE_WAIT

FINbit=1 seq=y

ACKbit=1 ACKnum=y+1


close

can stillsend data


LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2max

segment lifetime

CLOSED



clientSocketclose()











control





a top-10 problem








Host A

original data in

Host B

throughput out

R2

R2

out

in R2de

lay








Host A

in original data

Host B


lsquo








free buffer space

R2

R2

out

in


Host B

A




no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







rsquo increase


Host A out


Host B

Host CHost D


retransmitted data







C2

C2

out

inrsquo










control





loss

cwnd

TCP

send

er

cong

estio

n w

indo

w s

ize


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwndRTT

bytessec






Host A

RTT

Host B

time



















cwnd gt ssthresh

congestionavoidance



new ACK


fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


WRTT bytessec










TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R






















linkphysical


linkphysical

ECN=00 ECN=11

ECE=1

IP datagram

TCP ACK segment






bull UDPbull TCP

next leaving the



Transport Layer 3-4









Transport Layer 3-5










household analogy

Transport Layer 3-6















data linkphysical

Transport Layer 3-7









control

Transport Layer 3-8


process

socket




transport

application

physicallink

network

P2P1

transport

application

physicallink

network

P4

transport

application

physicallink

network

P3

Transport Layer 3-9








32 bits

applicationdata

(payload)

other header fields













transport

application

physicallink

network

P3transport

application

physicallink

network

P1

transport

application

physicallink

network

P4

















transport

application

physicallink

network

P3transport

application

physicallink

P4

transport

application

physicallink

network

P2



host IP address

A

host IP address

C

network

P6P5P3




server IP

address B



transport

application

physicallink

network

P3transport

application

physicallink

transport

application

physicallink

network

P2



host IP address

A

host IP address

C

server IP

address B

network

P3



P4

threaded server










control













error recovery


UDP segment header


32 bits

applicationdata

(payload)

UDP segment format

length checksum


including header





why is there a UDP


UDP checksum














1 1 1 1 0 0 1 1 0 0 1 1 0 0 1 1 01 1 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1

1 1 0 1 1 1 0 1 1 1 0 1 1 1 0 1 1

1 1 0 1 1 1 0 1 1 1 0 1 1 1 1 0 01 0 1 0 0 0 1 0 0 0 1 0 0 0 0 1 1

wraparound

sumchecksum












control















sendside

receiveside










sender receiver

state1

state2




eventactions







udt_send(packet)


Wait for call from

below

rdt_rcv(packet)

sender receiver







gtsender









sender









udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

belowsender









udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)








udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)














above


rdt_send(data)




rdt_send(data)


udt_send(sndpkt)



Wait forcall 1 from

above




































above


rdt_send(data)

udt_send(sndpkt)


isACK(rcvpkt1) )


Wait for ACK

0sender FSMfragment





has_seq1(rcvpkt))


fragment













rdt_send(data)

Wait for

ACK0



above


rdt_send(data)






timeout


timeout

rdt_rcv(rcvpkt)

Wait for call 0from

above

Wait for

ACK1

rdt_rcv(rcvpkt)


sender receiver

rcv pkt1

rcv pkt0

send ack0

send ack1

send ack0

rcv ack0

send pkt0

send pkt1

rcv ack1

send pkt0rcv pkt0

pkt0

pkt0

pkt1

ack1

ack0

ack0

(a) no loss

sender receiver

rcv pkt1

rcv pkt0

send ack0

send ack1

send ack0

rcv ack0

send pkt0

send pkt1

rcv ack1

send pkt0rcv pkt0

pkt0

pkt0

ack1

ack0

ack0

(b) packet loss

pkt1X

loss

pkt1timeout

resend pkt1

rdt30 in action


rdt30 in action

rcv pkt1send ack1

(detect duplicate)

pkt1

sender receiver

rcv pkt1

rcv pkt0

send ack0

send ack1

send ack0

rcv ack0

send pkt0

send pkt1

rcv ack1

send pkt0rcv pkt0

pkt0

pkt0

ack1

ack0

ack0

(c) ACK loss

ack1X

loss

pkt1timeout

resend pkt1

rcv pkt1send ack1

(detect duplicate)

pkt1

sender receiver

rcv pkt1

send ack0rcv ack0

send pkt1

send pkt0rcv pkt0

pkt0

ack0


pkt1timeout

resend pkt1

ack1

send ack1

send pkt0rcv ack1

pkt0

ack1

ack0






packet


U sender =

008 30008

= 000027 L R RTT + L R

=



Dtrans = LR





sender receiver

RTT




U sender =

008 30008

= 000027 L R RTT + L R

=








RTT






U sender =

0024 30008

= 000081 3L R RTT + L R

=










ack for each packet







window




timeout

rdt_send(data)







base=1nextseqnum=1






Wait







GBN in action


(wait)

sender receiver



rcv ack1 send pkt5


Xloss





0 1 2 3 4 5 6 7 8

sender window (N=4)

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8










Selective repeat



timerACK(n) in








receiver




(wait)

sender receiver



rcv ack1 send pkt5


Xloss




record ack3 arrived

0 1 2 3 4 5 6 7 8

sender window (N=4)

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8







0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2

pkt0pkt1pkt2

0 1 2 3 0 1 2 pkt0


0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2XXX


0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2

pkt0pkt1pkt2

0 1 2 3 0 1 2pkt0

0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2


0 1 2 3 0 1 2 pkt3

(a) no problem















control









overwhelm receiver









32 bits

applicationdata

(variable length)


receive window


lennot

used



ACK ACK valid



commands)



Internetchecksum

(as in UDP)








checksum

rwndurg pointer


A

sent ACKed



not usable

window sizeN




checksum

rwndurg pointer





host ACKsreceipt




Host BHost A



Seq=43 ACK=80














100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106time (seconnds)

RTT

(mill

iseco

nds)






T (m

illise

cond

s)



time (seconds)






(typically = 025)













control









congestion control















waitfor

event



start timer



start timer

timeout






lost ACK scenario

Host BHost A


ACK=100


Xtimeo

ut

ACK=100

premature timeout

Host BHost A


ACK=100


timeo

ut

ACK=120


ACK=120

SendBase=100

SendBase=120

SendBase=120

SendBase=92



X

cumulative ACK

Host BHost A


ACK=100


timeo

ut


ACK=120



event at receiver





TCP receiver action














TCP fast retransmit



X


Host BHost A


ACK=100

timeo

ut ACK=100

ACK=100ACK=100

TCP fast retransmit












control



process


TCPcode

IPcode

applicationOS





from sender


flow control


TCP flow control

buffered data


RcvBuffer


















control








application

network




application

network








2-way handshake

Letrsquos talk

OKESTAB

ESTAB


ESTABacc_conn(x)





ESTAB

req_conn(x)


client terminates

serverforgets x



ESTAB

req_conn(x)

data(x+1)

retransmitdata(x+1)

acceptdata(x+1)

choose xreq_conn(x)

ESTAB

ESTAB

acc_conn(x)

client terminates

ESTAB

choose xreq_conn(x)

ESTABacc_conn(x)



forgets x


TCP 3-way handshake

SYNbit=1 Seq=x


ESTAB



ACKbit=1 ACKnum=y+1




SYNSENT

ESTAB

SYN RCVD

client stateLISTEN

server stateLISTEN



closed

listen

SYNrcvd

SYNsent

ESTAB


SYN(seq=x)











FIN_WAIT_2

CLOSE_WAIT

FINbit=1 seq=y

ACKbit=1 ACKnum=y+1


close

can stillsend data


LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2max

segment lifetime

CLOSED



clientSocketclose()











control





a top-10 problem








Host A

original data in

Host B

throughput out

R2

R2

out

in R2de

lay








Host A

in original data

Host B


lsquo








free buffer space

R2

R2

out

in


Host B

A




no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







rsquo increase


Host A out


Host B

Host CHost D


retransmitted data







C2

C2

out

inrsquo










control





loss

cwnd

TCP

send

er

cong

estio

n w

indo

w s

ize


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwndRTT

bytessec






Host A

RTT

Host B

time



















cwnd gt ssthresh

congestionavoidance



new ACK


fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


WRTT bytessec










TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R






















linkphysical


linkphysical

ECN=00 ECN=11

ECE=1

IP datagram

TCP ACK segment






bull UDPbull TCP

next leaving the



Transport Layer 3-5










household analogy

Transport Layer 3-6















data linkphysical

Transport Layer 3-7









control

Transport Layer 3-8


process

socket




transport

application

physicallink

network

P2P1

transport

application

physicallink

network

P4

transport

application

physicallink

network

P3

Transport Layer 3-9








32 bits

applicationdata

(payload)

other header fields













transport

application

physicallink

network

P3transport

application

physicallink

network

P1

transport

application

physicallink

network

P4

















transport

application

physicallink

network

P3transport

application

physicallink

P4

transport

application

physicallink

network

P2



host IP address

A

host IP address

C

network

P6P5P3




server IP

address B



transport

application

physicallink

network

P3transport

application

physicallink

transport

application

physicallink

network

P2



host IP address

A

host IP address

C

server IP

address B

network

P3



P4

threaded server










control













error recovery


UDP segment header


32 bits

applicationdata

(payload)

UDP segment format

length checksum


including header





why is there a UDP


UDP checksum














1 1 1 1 0 0 1 1 0 0 1 1 0 0 1 1 01 1 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1

1 1 0 1 1 1 0 1 1 1 0 1 1 1 0 1 1

1 1 0 1 1 1 0 1 1 1 0 1 1 1 1 0 01 0 1 0 0 0 1 0 0 0 1 0 0 0 0 1 1

wraparound

sumchecksum












control















sendside

receiveside










sender receiver

state1

state2




eventactions







udt_send(packet)


Wait for call from

below

rdt_rcv(packet)

sender receiver







gtsender









sender









udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

belowsender









udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)








udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)














above


rdt_send(data)




rdt_send(data)


udt_send(sndpkt)



Wait forcall 1 from

above




































above


rdt_send(data)

udt_send(sndpkt)


isACK(rcvpkt1) )


Wait for ACK

0sender FSMfragment





has_seq1(rcvpkt))


fragment













rdt_send(data)

Wait for

ACK0



above


rdt_send(data)






timeout


timeout

rdt_rcv(rcvpkt)

Wait for call 0from

above

Wait for

ACK1

rdt_rcv(rcvpkt)


sender receiver

rcv pkt1

rcv pkt0

send ack0

send ack1

send ack0

rcv ack0

send pkt0

send pkt1

rcv ack1

send pkt0rcv pkt0

pkt0

pkt0

pkt1

ack1

ack0

ack0

(a) no loss

sender receiver

rcv pkt1

rcv pkt0

send ack0

send ack1

send ack0

rcv ack0

send pkt0

send pkt1

rcv ack1

send pkt0rcv pkt0

pkt0

pkt0

ack1

ack0

ack0

(b) packet loss

pkt1X

loss

pkt1timeout

resend pkt1

rdt30 in action


rdt30 in action

rcv pkt1send ack1

(detect duplicate)

pkt1

sender receiver

rcv pkt1

rcv pkt0

send ack0

send ack1

send ack0

rcv ack0

send pkt0

send pkt1

rcv ack1

send pkt0rcv pkt0

pkt0

pkt0

ack1

ack0

ack0

(c) ACK loss

ack1X

loss

pkt1timeout

resend pkt1

rcv pkt1send ack1

(detect duplicate)

pkt1

sender receiver

rcv pkt1

send ack0rcv ack0

send pkt1

send pkt0rcv pkt0

pkt0

ack0


pkt1timeout

resend pkt1

ack1

send ack1

send pkt0rcv ack1

pkt0

ack1

ack0






packet


U sender =

008 30008

= 000027 L R RTT + L R

=



Dtrans = LR





sender receiver

RTT




U sender =

008 30008

= 000027 L R RTT + L R

=








RTT






U sender =

0024 30008

= 000081 3L R RTT + L R

=










ack for each packet







window




timeout

rdt_send(data)







base=1nextseqnum=1






Wait







GBN in action


(wait)

sender receiver



rcv ack1 send pkt5


Xloss





0 1 2 3 4 5 6 7 8

sender window (N=4)

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8










Selective repeat



timerACK(n) in








receiver




(wait)

sender receiver



rcv ack1 send pkt5


Xloss




record ack3 arrived

0 1 2 3 4 5 6 7 8

sender window (N=4)

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8







0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2

pkt0pkt1pkt2

0 1 2 3 0 1 2 pkt0


0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2XXX


0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2

pkt0pkt1pkt2

0 1 2 3 0 1 2pkt0

0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2


0 1 2 3 0 1 2 pkt3

(a) no problem















control









overwhelm receiver









32 bits

applicationdata

(variable length)


receive window


lennot

used



ACK ACK valid



commands)



Internetchecksum

(as in UDP)








checksum

rwndurg pointer


A

sent ACKed



not usable

window sizeN




checksum

rwndurg pointer





host ACKsreceipt




Host BHost A



Seq=43 ACK=80














100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106time (seconnds)

RTT

(mill

iseco

nds)






T (m

illise

cond

s)



time (seconds)






(typically = 025)













control









congestion control















waitfor

event



start timer



start timer

timeout






lost ACK scenario

Host BHost A


ACK=100


Xtimeo

ut

ACK=100

premature timeout

Host BHost A


ACK=100


timeo

ut

ACK=120


ACK=120

SendBase=100

SendBase=120

SendBase=120

SendBase=92



X

cumulative ACK

Host BHost A


ACK=100


timeo

ut


ACK=120



event at receiver





TCP receiver action














TCP fast retransmit



X


Host BHost A


ACK=100

timeo

ut ACK=100

ACK=100ACK=100

TCP fast retransmit












control



process


TCPcode

IPcode

applicationOS





from sender


flow control


TCP flow control

buffered data


RcvBuffer


















control








application

network




application

network








2-way handshake

Letrsquos talk

OKESTAB

ESTAB


ESTABacc_conn(x)





ESTAB

req_conn(x)


client terminates

serverforgets x



ESTAB

req_conn(x)

data(x+1)

retransmitdata(x+1)

acceptdata(x+1)

choose xreq_conn(x)

ESTAB

ESTAB

acc_conn(x)

client terminates

ESTAB

choose xreq_conn(x)

ESTABacc_conn(x)



forgets x


TCP 3-way handshake

SYNbit=1 Seq=x


ESTAB



ACKbit=1 ACKnum=y+1




SYNSENT

ESTAB

SYN RCVD

client stateLISTEN

server stateLISTEN



closed

listen

SYNrcvd

SYNsent

ESTAB


SYN(seq=x)











FIN_WAIT_2

CLOSE_WAIT

FINbit=1 seq=y

ACKbit=1 ACKnum=y+1


close

can stillsend data


LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2max

segment lifetime

CLOSED



clientSocketclose()











control





a top-10 problem








Host A

original data in

Host B

throughput out

R2

R2

out

in R2de

lay








Host A

in original data

Host B


lsquo








free buffer space

R2

R2

out

in


Host B

A




no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







rsquo increase


Host A out


Host B

Host CHost D


retransmitted data







C2

C2

out

inrsquo










control





loss

cwnd

TCP

send

er

cong

estio

n w

indo

w s

ize


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwndRTT

bytessec






Host A

RTT

Host B

time



















cwnd gt ssthresh

congestionavoidance



new ACK


fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


WRTT bytessec










TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R






















linkphysical


linkphysical

ECN=00 ECN=11

ECE=1

IP datagram

TCP ACK segment






bull UDPbull TCP

next leaving the



Transport Layer 3-6















data linkphysical

Transport Layer 3-7









control

Transport Layer 3-8


process

socket




transport

application

physicallink

network

P2P1

transport

application

physicallink

network

P4

transport

application

physicallink

network

P3

Transport Layer 3-9








32 bits

applicationdata

(payload)

other header fields













transport

application

physicallink

network

P3transport

application

physicallink

network

P1

transport

application

physicallink

network

P4

















transport

application

physicallink

network

P3transport

application

physicallink

P4

transport

application

physicallink

network

P2



host IP address

A

host IP address

C

network

P6P5P3




server IP

address B



transport

application

physicallink

network

P3transport

application

physicallink

transport

application

physicallink

network

P2



host IP address

A

host IP address

C

server IP

address B

network

P3



P4

threaded server










control













error recovery


UDP segment header


32 bits

applicationdata

(payload)

UDP segment format

length checksum


including header





why is there a UDP


UDP checksum














1 1 1 1 0 0 1 1 0 0 1 1 0 0 1 1 01 1 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1

1 1 0 1 1 1 0 1 1 1 0 1 1 1 0 1 1

1 1 0 1 1 1 0 1 1 1 0 1 1 1 1 0 01 0 1 0 0 0 1 0 0 0 1 0 0 0 0 1 1

wraparound

sumchecksum












control















sendside

receiveside










sender receiver

state1

state2




eventactions







udt_send(packet)


Wait for call from

below

rdt_rcv(packet)

sender receiver







gtsender









sender









udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

belowsender









udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)








udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)














above


rdt_send(data)




rdt_send(data)


udt_send(sndpkt)



Wait forcall 1 from

above




































above


rdt_send(data)

udt_send(sndpkt)


isACK(rcvpkt1) )


Wait for ACK

0sender FSMfragment





has_seq1(rcvpkt))


fragment













rdt_send(data)

Wait for

ACK0



above


rdt_send(data)






timeout


timeout

rdt_rcv(rcvpkt)

Wait for call 0from

above

Wait for

ACK1

rdt_rcv(rcvpkt)


sender receiver

rcv pkt1

rcv pkt0

send ack0

send ack1

send ack0

rcv ack0

send pkt0

send pkt1

rcv ack1

send pkt0rcv pkt0

pkt0

pkt0

pkt1

ack1

ack0

ack0

(a) no loss

sender receiver

rcv pkt1

rcv pkt0

send ack0

send ack1

send ack0

rcv ack0

send pkt0

send pkt1

rcv ack1

send pkt0rcv pkt0

pkt0

pkt0

ack1

ack0

ack0

(b) packet loss

pkt1X

loss

pkt1timeout

resend pkt1

rdt30 in action


rdt30 in action

rcv pkt1send ack1

(detect duplicate)

pkt1

sender receiver

rcv pkt1

rcv pkt0

send ack0

send ack1

send ack0

rcv ack0

send pkt0

send pkt1

rcv ack1

send pkt0rcv pkt0

pkt0

pkt0

ack1

ack0

ack0

(c) ACK loss

ack1X

loss

pkt1timeout

resend pkt1

rcv pkt1send ack1

(detect duplicate)

pkt1

sender receiver

rcv pkt1

send ack0rcv ack0

send pkt1

send pkt0rcv pkt0

pkt0

ack0


pkt1timeout

resend pkt1

ack1

send ack1

send pkt0rcv ack1

pkt0

ack1

ack0






packet


U sender =

008 30008

= 000027 L R RTT + L R

=



Dtrans = LR





sender receiver

RTT




U sender =

008 30008

= 000027 L R RTT + L R

=








RTT






U sender =

0024 30008

= 000081 3L R RTT + L R

=










ack for each packet







window




timeout

rdt_send(data)







base=1nextseqnum=1






Wait







GBN in action


(wait)

sender receiver



rcv ack1 send pkt5


Xloss





0 1 2 3 4 5 6 7 8

sender window (N=4)

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8










Selective repeat



timerACK(n) in








receiver




(wait)

sender receiver



rcv ack1 send pkt5


Xloss




record ack3 arrived

0 1 2 3 4 5 6 7 8

sender window (N=4)

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8







0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2

pkt0pkt1pkt2

0 1 2 3 0 1 2 pkt0


0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2XXX


0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2

pkt0pkt1pkt2

0 1 2 3 0 1 2pkt0

0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2


0 1 2 3 0 1 2 pkt3

(a) no problem















control









overwhelm receiver









32 bits

applicationdata

(variable length)


receive window


lennot

used



ACK ACK valid



commands)



Internetchecksum

(as in UDP)








checksum

rwndurg pointer


A

sent ACKed



not usable

window sizeN




checksum

rwndurg pointer





host ACKsreceipt




Host BHost A



Seq=43 ACK=80














100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106time (seconnds)

RTT

(mill

iseco

nds)






T (m

illise

cond

s)



time (seconds)






(typically = 025)













control









congestion control















waitfor

event



start timer



start timer

timeout






lost ACK scenario

Host BHost A


ACK=100


Xtimeo

ut

ACK=100

premature timeout

Host BHost A


ACK=100


timeo

ut

ACK=120


ACK=120

SendBase=100

SendBase=120

SendBase=120

SendBase=92



X

cumulative ACK

Host BHost A


ACK=100


timeo

ut


ACK=120



event at receiver





TCP receiver action














TCP fast retransmit



X


Host BHost A


ACK=100

timeo

ut ACK=100

ACK=100ACK=100

TCP fast retransmit












control



process


TCPcode

IPcode

applicationOS





from sender


flow control


TCP flow control

buffered data


RcvBuffer


















control








application

network




application

network








2-way handshake

Letrsquos talk

OKESTAB

ESTAB


ESTABacc_conn(x)





ESTAB

req_conn(x)


client terminates

serverforgets x



ESTAB

req_conn(x)

data(x+1)

retransmitdata(x+1)

acceptdata(x+1)

choose xreq_conn(x)

ESTAB

ESTAB

acc_conn(x)

client terminates

ESTAB

choose xreq_conn(x)

ESTABacc_conn(x)



forgets x


TCP 3-way handshake

SYNbit=1 Seq=x


ESTAB



ACKbit=1 ACKnum=y+1




SYNSENT

ESTAB

SYN RCVD

client stateLISTEN

server stateLISTEN



closed

listen

SYNrcvd

SYNsent

ESTAB


SYN(seq=x)











FIN_WAIT_2

CLOSE_WAIT

FINbit=1 seq=y

ACKbit=1 ACKnum=y+1


close

can stillsend data


LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2max

segment lifetime

CLOSED



clientSocketclose()











control





a top-10 problem








Host A

original data in

Host B

throughput out

R2

R2

out

in R2de

lay








Host A

in original data

Host B


lsquo








free buffer space

R2

R2

out

in


Host B

A




no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







rsquo increase


Host A out


Host B

Host CHost D


retransmitted data







C2

C2

out

inrsquo










control





loss

cwnd

TCP

send

er

cong

estio

n w

indo

w s

ize


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwndRTT

bytessec






Host A

RTT

Host B

time



















cwnd gt ssthresh

congestionavoidance



new ACK


fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


WRTT bytessec










TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R






















linkphysical


linkphysical

ECN=00 ECN=11

ECE=1

IP datagram

TCP ACK segment






bull UDPbull TCP

next leaving the



Transport Layer 3-7









control

Transport Layer 3-8


process

socket




transport

application

physicallink

network

P2P1

transport

application

physicallink

network

P4

transport

application

physicallink

network

P3

Transport Layer 3-9








32 bits

applicationdata

(payload)

other header fields













transport

application

physicallink

network

P3transport

application

physicallink

network

P1

transport

application

physicallink

network

P4

















transport

application

physicallink

network

P3transport

application

physicallink

P4

transport

application

physicallink

network

P2



host IP address

A

host IP address

C

network

P6P5P3




server IP

address B



transport

application

physicallink

network

P3transport

application

physicallink

transport

application

physicallink

network

P2



host IP address

A

host IP address

C

server IP

address B

network

P3



P4

threaded server










control













error recovery


UDP segment header


32 bits

applicationdata

(payload)

UDP segment format

length checksum


including header





why is there a UDP


UDP checksum














1 1 1 1 0 0 1 1 0 0 1 1 0 0 1 1 01 1 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1

1 1 0 1 1 1 0 1 1 1 0 1 1 1 0 1 1

1 1 0 1 1 1 0 1 1 1 0 1 1 1 1 0 01 0 1 0 0 0 1 0 0 0 1 0 0 0 0 1 1

wraparound

sumchecksum












control















sendside

receiveside










sender receiver

state1

state2




eventactions







udt_send(packet)


Wait for call from

below

rdt_rcv(packet)

sender receiver







gtsender









sender









udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

belowsender









udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)








udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)














above


rdt_send(data)




rdt_send(data)


udt_send(sndpkt)



Wait forcall 1 from

above




































above


rdt_send(data)

udt_send(sndpkt)


isACK(rcvpkt1) )


Wait for ACK

0sender FSMfragment





has_seq1(rcvpkt))


fragment













rdt_send(data)

Wait for

ACK0



above


rdt_send(data)






timeout


timeout

rdt_rcv(rcvpkt)

Wait for call 0from

above

Wait for

ACK1

rdt_rcv(rcvpkt)


sender receiver

rcv pkt1

rcv pkt0

send ack0

send ack1

send ack0

rcv ack0

send pkt0

send pkt1

rcv ack1

send pkt0rcv pkt0

pkt0

pkt0

pkt1

ack1

ack0

ack0

(a) no loss

sender receiver

rcv pkt1

rcv pkt0

send ack0

send ack1

send ack0

rcv ack0

send pkt0

send pkt1

rcv ack1

send pkt0rcv pkt0

pkt0

pkt0

ack1

ack0

ack0

(b) packet loss

pkt1X

loss

pkt1timeout

resend pkt1

rdt30 in action


rdt30 in action

rcv pkt1send ack1

(detect duplicate)

pkt1

sender receiver

rcv pkt1

rcv pkt0

send ack0

send ack1

send ack0

rcv ack0

send pkt0

send pkt1

rcv ack1

send pkt0rcv pkt0

pkt0

pkt0

ack1

ack0

ack0

(c) ACK loss

ack1X

loss

pkt1timeout

resend pkt1

rcv pkt1send ack1

(detect duplicate)

pkt1

sender receiver

rcv pkt1

send ack0rcv ack0

send pkt1

send pkt0rcv pkt0

pkt0

ack0


pkt1timeout

resend pkt1

ack1

send ack1

send pkt0rcv ack1

pkt0

ack1

ack0






packet


U sender =

008 30008

= 000027 L R RTT + L R

=



Dtrans = LR





sender receiver

RTT




U sender =

008 30008

= 000027 L R RTT + L R

=








RTT






U sender =

0024 30008

= 000081 3L R RTT + L R

=










ack for each packet







window




timeout

rdt_send(data)







base=1nextseqnum=1






Wait







GBN in action


(wait)

sender receiver



rcv ack1 send pkt5


Xloss





0 1 2 3 4 5 6 7 8

sender window (N=4)

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8










Selective repeat



timerACK(n) in








receiver




(wait)

sender receiver



rcv ack1 send pkt5


Xloss




record ack3 arrived

0 1 2 3 4 5 6 7 8

sender window (N=4)

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8







0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2

pkt0pkt1pkt2

0 1 2 3 0 1 2 pkt0


0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2XXX


0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2

pkt0pkt1pkt2

0 1 2 3 0 1 2pkt0

0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2


0 1 2 3 0 1 2 pkt3

(a) no problem















control









overwhelm receiver









32 bits

applicationdata

(variable length)


receive window


lennot

used



ACK ACK valid



commands)



Internetchecksum

(as in UDP)








checksum

rwndurg pointer


A

sent ACKed



not usable

window sizeN




checksum

rwndurg pointer





host ACKsreceipt




Host BHost A



Seq=43 ACK=80














100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106time (seconnds)

RTT

(mill

iseco

nds)






T (m

illise

cond

s)



time (seconds)






(typically = 025)













control









congestion control















waitfor

event



start timer



start timer

timeout






lost ACK scenario

Host BHost A


ACK=100


Xtimeo

ut

ACK=100

premature timeout

Host BHost A


ACK=100


timeo

ut

ACK=120


ACK=120

SendBase=100

SendBase=120

SendBase=120

SendBase=92



X

cumulative ACK

Host BHost A


ACK=100


timeo

ut


ACK=120



event at receiver





TCP receiver action














TCP fast retransmit



X


Host BHost A


ACK=100

timeo

ut ACK=100

ACK=100ACK=100

TCP fast retransmit












control



process


TCPcode

IPcode

applicationOS





from sender


flow control


TCP flow control

buffered data


RcvBuffer


















control








application

network




application

network








2-way handshake

Letrsquos talk

OKESTAB

ESTAB


ESTABacc_conn(x)





ESTAB

req_conn(x)


client terminates

serverforgets x



ESTAB

req_conn(x)

data(x+1)

retransmitdata(x+1)

acceptdata(x+1)

choose xreq_conn(x)

ESTAB

ESTAB

acc_conn(x)

client terminates

ESTAB

choose xreq_conn(x)

ESTABacc_conn(x)



forgets x


TCP 3-way handshake

SYNbit=1 Seq=x


ESTAB



ACKbit=1 ACKnum=y+1




SYNSENT

ESTAB

SYN RCVD

client stateLISTEN

server stateLISTEN



closed

listen

SYNrcvd

SYNsent

ESTAB


SYN(seq=x)











FIN_WAIT_2

CLOSE_WAIT

FINbit=1 seq=y

ACKbit=1 ACKnum=y+1


close

can stillsend data


LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2max

segment lifetime

CLOSED



clientSocketclose()











control





a top-10 problem








Host A

original data in

Host B

throughput out

R2

R2

out

in R2de

lay








Host A

in original data

Host B


lsquo








free buffer space

R2

R2

out

in


Host B

A




no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







rsquo increase


Host A out


Host B

Host CHost D


retransmitted data







C2

C2

out

inrsquo










control





loss

cwnd

TCP

send

er

cong

estio

n w

indo

w s

ize


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwndRTT

bytessec






Host A

RTT

Host B

time



















cwnd gt ssthresh

congestionavoidance



new ACK


fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


WRTT bytessec










TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R






















linkphysical


linkphysical

ECN=00 ECN=11

ECE=1

IP datagram

TCP ACK segment






bull UDPbull TCP

next leaving the



Transport Layer 3-8


process

socket




transport

application

physicallink

network

P2P1

transport

application

physicallink

network

P4

transport

application

physicallink

network

P3

Transport Layer 3-9








32 bits

applicationdata

(payload)

other header fields













transport

application

physicallink

network

P3transport

application

physicallink

network

P1

transport

application

physicallink

network

P4

















transport

application

physicallink

network

P3transport

application

physicallink

P4

transport

application

physicallink

network

P2



host IP address

A

host IP address

C

network

P6P5P3




server IP

address B



transport

application

physicallink

network

P3transport

application

physicallink

transport

application

physicallink

network

P2



host IP address

A

host IP address

C

server IP

address B

network

P3



P4

threaded server










control













error recovery


UDP segment header


32 bits

applicationdata

(payload)

UDP segment format

length checksum


including header





why is there a UDP


UDP checksum














1 1 1 1 0 0 1 1 0 0 1 1 0 0 1 1 01 1 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1

1 1 0 1 1 1 0 1 1 1 0 1 1 1 0 1 1

1 1 0 1 1 1 0 1 1 1 0 1 1 1 1 0 01 0 1 0 0 0 1 0 0 0 1 0 0 0 0 1 1

wraparound

sumchecksum












control















sendside

receiveside










sender receiver

state1

state2




eventactions







udt_send(packet)


Wait for call from

below

rdt_rcv(packet)

sender receiver







gtsender









sender









udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

belowsender









udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)








udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)














above


rdt_send(data)




rdt_send(data)


udt_send(sndpkt)



Wait forcall 1 from

above




































above


rdt_send(data)

udt_send(sndpkt)


isACK(rcvpkt1) )


Wait for ACK

0sender FSMfragment





has_seq1(rcvpkt))


fragment













rdt_send(data)

Wait for

ACK0



above


rdt_send(data)






timeout


timeout

rdt_rcv(rcvpkt)

Wait for call 0from

above

Wait for

ACK1

rdt_rcv(rcvpkt)


sender receiver

rcv pkt1

rcv pkt0

send ack0

send ack1

send ack0

rcv ack0

send pkt0

send pkt1

rcv ack1

send pkt0rcv pkt0

pkt0

pkt0

pkt1

ack1

ack0

ack0

(a) no loss

sender receiver

rcv pkt1

rcv pkt0

send ack0

send ack1

send ack0

rcv ack0

send pkt0

send pkt1

rcv ack1

send pkt0rcv pkt0

pkt0

pkt0

ack1

ack0

ack0

(b) packet loss

pkt1X

loss

pkt1timeout

resend pkt1

rdt30 in action


rdt30 in action

rcv pkt1send ack1

(detect duplicate)

pkt1

sender receiver

rcv pkt1

rcv pkt0

send ack0

send ack1

send ack0

rcv ack0

send pkt0

send pkt1

rcv ack1

send pkt0rcv pkt0

pkt0

pkt0

ack1

ack0

ack0

(c) ACK loss

ack1X

loss

pkt1timeout

resend pkt1

rcv pkt1send ack1

(detect duplicate)

pkt1

sender receiver

rcv pkt1

send ack0rcv ack0

send pkt1

send pkt0rcv pkt0

pkt0

ack0


pkt1timeout

resend pkt1

ack1

send ack1

send pkt0rcv ack1

pkt0

ack1

ack0






packet


U sender =

008 30008

= 000027 L R RTT + L R

=



Dtrans = LR





sender receiver

RTT




U sender =

008 30008

= 000027 L R RTT + L R

=








RTT






U sender =

0024 30008

= 000081 3L R RTT + L R

=










ack for each packet







window




timeout

rdt_send(data)







base=1nextseqnum=1






Wait







GBN in action


(wait)

sender receiver



rcv ack1 send pkt5


Xloss





0 1 2 3 4 5 6 7 8

sender window (N=4)

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8










Selective repeat



timerACK(n) in








receiver




(wait)

sender receiver



rcv ack1 send pkt5


Xloss




record ack3 arrived

0 1 2 3 4 5 6 7 8

sender window (N=4)

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8







0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2

pkt0pkt1pkt2

0 1 2 3 0 1 2 pkt0


0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2XXX


0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2

pkt0pkt1pkt2

0 1 2 3 0 1 2pkt0

0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2


0 1 2 3 0 1 2 pkt3

(a) no problem















control









overwhelm receiver









32 bits

applicationdata

(variable length)


receive window


lennot

used



ACK ACK valid



commands)



Internetchecksum

(as in UDP)








checksum

rwndurg pointer


A

sent ACKed



not usable

window sizeN




checksum

rwndurg pointer





host ACKsreceipt




Host BHost A



Seq=43 ACK=80














100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106time (seconnds)

RTT

(mill

iseco

nds)






T (m

illise

cond

s)



time (seconds)






(typically = 025)













control









congestion control















waitfor

event



start timer



start timer

timeout






lost ACK scenario

Host BHost A


ACK=100


Xtimeo

ut

ACK=100

premature timeout

Host BHost A


ACK=100


timeo

ut

ACK=120


ACK=120

SendBase=100

SendBase=120

SendBase=120

SendBase=92



X

cumulative ACK

Host BHost A


ACK=100


timeo

ut


ACK=120



event at receiver





TCP receiver action














TCP fast retransmit



X


Host BHost A


ACK=100

timeo

ut ACK=100

ACK=100ACK=100

TCP fast retransmit












control



process


TCPcode

IPcode

applicationOS





from sender


flow control


TCP flow control

buffered data


RcvBuffer


















control








application

network




application

network








2-way handshake

Letrsquos talk

OKESTAB

ESTAB


ESTABacc_conn(x)





ESTAB

req_conn(x)


client terminates

serverforgets x



ESTAB

req_conn(x)

data(x+1)

retransmitdata(x+1)

acceptdata(x+1)

choose xreq_conn(x)

ESTAB

ESTAB

acc_conn(x)

client terminates

ESTAB

choose xreq_conn(x)

ESTABacc_conn(x)



forgets x


TCP 3-way handshake

SYNbit=1 Seq=x


ESTAB



ACKbit=1 ACKnum=y+1




SYNSENT

ESTAB

SYN RCVD

client stateLISTEN

server stateLISTEN



closed

listen

SYNrcvd

SYNsent

ESTAB


SYN(seq=x)











FIN_WAIT_2

CLOSE_WAIT

FINbit=1 seq=y

ACKbit=1 ACKnum=y+1


close

can stillsend data


LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2max

segment lifetime

CLOSED



clientSocketclose()











control





a top-10 problem








Host A

original data in

Host B

throughput out

R2

R2

out

in R2de

lay








Host A

in original data

Host B


lsquo








free buffer space

R2

R2

out

in


Host B

A




no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







rsquo increase


Host A out


Host B

Host CHost D


retransmitted data







C2

C2

out

inrsquo










control





loss

cwnd

TCP

send

er

cong

estio

n w

indo

w s

ize


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwndRTT

bytessec






Host A

RTT

Host B

time



















cwnd gt ssthresh

congestionavoidance



new ACK


fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


WRTT bytessec










TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R






















linkphysical


linkphysical

ECN=00 ECN=11

ECE=1

IP datagram

TCP ACK segment






bull UDPbull TCP

next leaving the



Transport Layer 3-9








32 bits

applicationdata

(payload)

other header fields













transport

application

physicallink

network

P3transport

application

physicallink

network

P1

transport

application

physicallink

network

P4

















transport

application

physicallink

network

P3transport

application

physicallink

P4

transport

application

physicallink

network

P2



host IP address

A

host IP address

C

network

P6P5P3




server IP

address B



transport

application

physicallink

network

P3transport

application

physicallink

transport

application

physicallink

network

P2



host IP address

A

host IP address

C

server IP

address B

network

P3



P4

threaded server










control













error recovery


UDP segment header


32 bits

applicationdata

(payload)

UDP segment format

length checksum


including header





why is there a UDP


UDP checksum














1 1 1 1 0 0 1 1 0 0 1 1 0 0 1 1 01 1 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1

1 1 0 1 1 1 0 1 1 1 0 1 1 1 0 1 1

1 1 0 1 1 1 0 1 1 1 0 1 1 1 1 0 01 0 1 0 0 0 1 0 0 0 1 0 0 0 0 1 1

wraparound

sumchecksum












control















sendside

receiveside










sender receiver

state1

state2




eventactions







udt_send(packet)


Wait for call from

below

rdt_rcv(packet)

sender receiver







gtsender









sender









udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

belowsender









udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)








udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)














above


rdt_send(data)




rdt_send(data)


udt_send(sndpkt)



Wait forcall 1 from

above




































above


rdt_send(data)

udt_send(sndpkt)


isACK(rcvpkt1) )


Wait for ACK

0sender FSMfragment





has_seq1(rcvpkt))


fragment













rdt_send(data)

Wait for

ACK0



above


rdt_send(data)






timeout


timeout

rdt_rcv(rcvpkt)

Wait for call 0from

above

Wait for

ACK1

rdt_rcv(rcvpkt)


sender receiver

rcv pkt1

rcv pkt0

send ack0

send ack1

send ack0

rcv ack0

send pkt0

send pkt1

rcv ack1

send pkt0rcv pkt0

pkt0

pkt0

pkt1

ack1

ack0

ack0

(a) no loss

sender receiver

rcv pkt1

rcv pkt0

send ack0

send ack1

send ack0

rcv ack0

send pkt0

send pkt1

rcv ack1

send pkt0rcv pkt0

pkt0

pkt0

ack1

ack0

ack0

(b) packet loss

pkt1X

loss

pkt1timeout

resend pkt1

rdt30 in action


rdt30 in action

rcv pkt1send ack1

(detect duplicate)

pkt1

sender receiver

rcv pkt1

rcv pkt0

send ack0

send ack1

send ack0

rcv ack0

send pkt0

send pkt1

rcv ack1

send pkt0rcv pkt0

pkt0

pkt0

ack1

ack0

ack0

(c) ACK loss

ack1X

loss

pkt1timeout

resend pkt1

rcv pkt1send ack1

(detect duplicate)

pkt1

sender receiver

rcv pkt1

send ack0rcv ack0

send pkt1

send pkt0rcv pkt0

pkt0

ack0


pkt1timeout

resend pkt1

ack1

send ack1

send pkt0rcv ack1

pkt0

ack1

ack0






packet


U sender =

008 30008

= 000027 L R RTT + L R

=



Dtrans = LR





sender receiver

RTT




U sender =

008 30008

= 000027 L R RTT + L R

=








RTT






U sender =

0024 30008

= 000081 3L R RTT + L R

=










ack for each packet







window




timeout

rdt_send(data)







base=1nextseqnum=1






Wait







GBN in action


(wait)

sender receiver



rcv ack1 send pkt5


Xloss





0 1 2 3 4 5 6 7 8

sender window (N=4)

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8










Selective repeat



timerACK(n) in








receiver




(wait)

sender receiver



rcv ack1 send pkt5


Xloss




record ack3 arrived

0 1 2 3 4 5 6 7 8

sender window (N=4)

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8







0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2

pkt0pkt1pkt2

0 1 2 3 0 1 2 pkt0


0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2XXX


0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2

pkt0pkt1pkt2

0 1 2 3 0 1 2pkt0

0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2


0 1 2 3 0 1 2 pkt3

(a) no problem















control









overwhelm receiver









32 bits

applicationdata

(variable length)


receive window


lennot

used



ACK ACK valid



commands)



Internetchecksum

(as in UDP)








checksum

rwndurg pointer


A

sent ACKed



not usable

window sizeN




checksum

rwndurg pointer





host ACKsreceipt




Host BHost A



Seq=43 ACK=80














100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106time (seconnds)

RTT

(mill

iseco

nds)






T (m

illise

cond

s)



time (seconds)






(typically = 025)













control









congestion control















waitfor

event



start timer



start timer

timeout






lost ACK scenario

Host BHost A


ACK=100


Xtimeo

ut

ACK=100

premature timeout

Host BHost A


ACK=100


timeo

ut

ACK=120


ACK=120

SendBase=100

SendBase=120

SendBase=120

SendBase=92



X

cumulative ACK

Host BHost A


ACK=100


timeo

ut


ACK=120



event at receiver





TCP receiver action














TCP fast retransmit



X


Host BHost A


ACK=100

timeo

ut ACK=100

ACK=100ACK=100

TCP fast retransmit












control



process


TCPcode

IPcode

applicationOS





from sender


flow control


TCP flow control

buffered data


RcvBuffer


















control








application

network




application

network








2-way handshake

Letrsquos talk

OKESTAB

ESTAB


ESTABacc_conn(x)





ESTAB

req_conn(x)


client terminates

serverforgets x



ESTAB

req_conn(x)

data(x+1)

retransmitdata(x+1)

acceptdata(x+1)

choose xreq_conn(x)

ESTAB

ESTAB

acc_conn(x)

client terminates

ESTAB

choose xreq_conn(x)

ESTABacc_conn(x)



forgets x


TCP 3-way handshake

SYNbit=1 Seq=x


ESTAB



ACKbit=1 ACKnum=y+1




SYNSENT

ESTAB

SYN RCVD

client stateLISTEN

server stateLISTEN



closed

listen

SYNrcvd

SYNsent

ESTAB


SYN(seq=x)











FIN_WAIT_2

CLOSE_WAIT

FINbit=1 seq=y

ACKbit=1 ACKnum=y+1


close

can stillsend data


LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2max

segment lifetime

CLOSED



clientSocketclose()











control





a top-10 problem








Host A

original data in

Host B

throughput out

R2

R2

out

in R2de

lay








Host A

in original data

Host B


lsquo








free buffer space

R2

R2

out

in


Host B

A




no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







rsquo increase


Host A out


Host B

Host CHost D


retransmitted data







C2

C2

out

inrsquo










control





loss

cwnd

TCP

send

er

cong

estio

n w

indo

w s

ize


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwndRTT

bytessec






Host A

RTT

Host B

time



















cwnd gt ssthresh

congestionavoidance



new ACK


fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


WRTT bytessec










TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R






















linkphysical


linkphysical

ECN=00 ECN=11

ECE=1

IP datagram

TCP ACK segment






bull UDPbull TCP

next leaving the














transport

application

physicallink

network

P3transport

application

physicallink

network

P1

transport

application

physicallink

network

P4

















transport

application

physicallink

network

P3transport

application

physicallink

P4

transport

application

physicallink

network

P2



host IP address

A

host IP address

C

network

P6P5P3




server IP

address B



transport

application

physicallink

network

P3transport

application

physicallink

transport

application

physicallink

network

P2



host IP address

A

host IP address

C

server IP

address B

network

P3



P4

threaded server










control













error recovery


UDP segment header


32 bits

applicationdata

(payload)

UDP segment format

length checksum


including header





why is there a UDP


UDP checksum














1 1 1 1 0 0 1 1 0 0 1 1 0 0 1 1 01 1 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1

1 1 0 1 1 1 0 1 1 1 0 1 1 1 0 1 1

1 1 0 1 1 1 0 1 1 1 0 1 1 1 1 0 01 0 1 0 0 0 1 0 0 0 1 0 0 0 0 1 1

wraparound

sumchecksum












control















sendside

receiveside










sender receiver

state1

state2




eventactions







udt_send(packet)


Wait for call from

below

rdt_rcv(packet)

sender receiver







gtsender









sender









udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

belowsender









udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)








udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)














above


rdt_send(data)




rdt_send(data)


udt_send(sndpkt)



Wait forcall 1 from

above




































above


rdt_send(data)

udt_send(sndpkt)


isACK(rcvpkt1) )


Wait for ACK

0sender FSMfragment





has_seq1(rcvpkt))


fragment













rdt_send(data)

Wait for

ACK0



above


rdt_send(data)






timeout


timeout

rdt_rcv(rcvpkt)

Wait for call 0from

above

Wait for

ACK1

rdt_rcv(rcvpkt)


sender receiver

rcv pkt1

rcv pkt0

send ack0

send ack1

send ack0

rcv ack0

send pkt0

send pkt1

rcv ack1

send pkt0rcv pkt0

pkt0

pkt0

pkt1

ack1

ack0

ack0

(a) no loss

sender receiver

rcv pkt1

rcv pkt0

send ack0

send ack1

send ack0

rcv ack0

send pkt0

send pkt1

rcv ack1

send pkt0rcv pkt0

pkt0

pkt0

ack1

ack0

ack0

(b) packet loss

pkt1X

loss

pkt1timeout

resend pkt1

rdt30 in action


rdt30 in action

rcv pkt1send ack1

(detect duplicate)

pkt1

sender receiver

rcv pkt1

rcv pkt0

send ack0

send ack1

send ack0

rcv ack0

send pkt0

send pkt1

rcv ack1

send pkt0rcv pkt0

pkt0

pkt0

ack1

ack0

ack0

(c) ACK loss

ack1X

loss

pkt1timeout

resend pkt1

rcv pkt1send ack1

(detect duplicate)

pkt1

sender receiver

rcv pkt1

send ack0rcv ack0

send pkt1

send pkt0rcv pkt0

pkt0

ack0


pkt1timeout

resend pkt1

ack1

send ack1

send pkt0rcv ack1

pkt0

ack1

ack0






packet


U sender =

008 30008

= 000027 L R RTT + L R

=



Dtrans = LR





sender receiver

RTT




U sender =

008 30008

= 000027 L R RTT + L R

=








RTT






U sender =

0024 30008

= 000081 3L R RTT + L R

=










ack for each packet







window




timeout

rdt_send(data)







base=1nextseqnum=1






Wait







GBN in action


(wait)

sender receiver



rcv ack1 send pkt5


Xloss





0 1 2 3 4 5 6 7 8

sender window (N=4)

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8










Selective repeat



timerACK(n) in








receiver




(wait)

sender receiver



rcv ack1 send pkt5


Xloss




record ack3 arrived

0 1 2 3 4 5 6 7 8

sender window (N=4)

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8







0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2

pkt0pkt1pkt2

0 1 2 3 0 1 2 pkt0


0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2XXX


0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2

pkt0pkt1pkt2

0 1 2 3 0 1 2pkt0

0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2


0 1 2 3 0 1 2 pkt3

(a) no problem















control









overwhelm receiver









32 bits

applicationdata

(variable length)


receive window


lennot

used



ACK ACK valid



commands)



Internetchecksum

(as in UDP)








checksum

rwndurg pointer


A

sent ACKed



not usable

window sizeN




checksum

rwndurg pointer





host ACKsreceipt




Host BHost A



Seq=43 ACK=80














100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106time (seconnds)

RTT

(mill

iseco

nds)






T (m

illise

cond

s)



time (seconds)






(typically = 025)













control









congestion control















waitfor

event



start timer



start timer

timeout






lost ACK scenario

Host BHost A


ACK=100


Xtimeo

ut

ACK=100

premature timeout

Host BHost A


ACK=100


timeo

ut

ACK=120


ACK=120

SendBase=100

SendBase=120

SendBase=120

SendBase=92



X

cumulative ACK

Host BHost A


ACK=100


timeo

ut


ACK=120



event at receiver





TCP receiver action














TCP fast retransmit



X


Host BHost A


ACK=100

timeo

ut ACK=100

ACK=100ACK=100

TCP fast retransmit












control



process


TCPcode

IPcode

applicationOS





from sender


flow control


TCP flow control

buffered data


RcvBuffer


















control








application

network




application

network








2-way handshake

Letrsquos talk

OKESTAB

ESTAB


ESTABacc_conn(x)





ESTAB

req_conn(x)


client terminates

serverforgets x



ESTAB

req_conn(x)

data(x+1)

retransmitdata(x+1)

acceptdata(x+1)

choose xreq_conn(x)

ESTAB

ESTAB

acc_conn(x)

client terminates

ESTAB

choose xreq_conn(x)

ESTABacc_conn(x)



forgets x


TCP 3-way handshake

SYNbit=1 Seq=x


ESTAB



ACKbit=1 ACKnum=y+1




SYNSENT

ESTAB

SYN RCVD

client stateLISTEN

server stateLISTEN



closed

listen

SYNrcvd

SYNsent

ESTAB


SYN(seq=x)











FIN_WAIT_2

CLOSE_WAIT

FINbit=1 seq=y

ACKbit=1 ACKnum=y+1


close

can stillsend data


LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2max

segment lifetime

CLOSED



clientSocketclose()











control





a top-10 problem








Host A

original data in

Host B

throughput out

R2

R2

out

in R2de

lay








Host A

in original data

Host B


lsquo








free buffer space

R2

R2

out

in


Host B

A




no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







rsquo increase


Host A out


Host B

Host CHost D


retransmitted data







C2

C2

out

inrsquo










control





loss

cwnd

TCP

send

er

cong

estio

n w

indo

w s

ize


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwndRTT

bytessec






Host A

RTT

Host B

time



















cwnd gt ssthresh

congestionavoidance



new ACK


fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


WRTT bytessec










TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R






















linkphysical


linkphysical

ECN=00 ECN=11

ECE=1

IP datagram

TCP ACK segment






bull UDPbull TCP

next leaving the













transport

application

physicallink

network

P3transport

application

physicallink

P4

transport

application

physicallink

network

P2



host IP address

A

host IP address

C

network

P6P5P3




server IP

address B



transport

application

physicallink

network

P3transport

application

physicallink

transport

application

physicallink

network

P2



host IP address

A

host IP address

C

server IP

address B

network

P3



P4

threaded server










control













error recovery


UDP segment header


32 bits

applicationdata

(payload)

UDP segment format

length checksum


including header





why is there a UDP


UDP checksum














1 1 1 1 0 0 1 1 0 0 1 1 0 0 1 1 01 1 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1

1 1 0 1 1 1 0 1 1 1 0 1 1 1 0 1 1

1 1 0 1 1 1 0 1 1 1 0 1 1 1 1 0 01 0 1 0 0 0 1 0 0 0 1 0 0 0 0 1 1

wraparound

sumchecksum












control















sendside

receiveside










sender receiver

state1

state2




eventactions







udt_send(packet)


Wait for call from

below

rdt_rcv(packet)

sender receiver







gtsender









sender









udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

belowsender









udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)








udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)














above


rdt_send(data)




rdt_send(data)


udt_send(sndpkt)



Wait forcall 1 from

above




































above


rdt_send(data)

udt_send(sndpkt)


isACK(rcvpkt1) )


Wait for ACK

0sender FSMfragment





has_seq1(rcvpkt))


fragment













rdt_send(data)

Wait for

ACK0



above


rdt_send(data)






timeout


timeout

rdt_rcv(rcvpkt)

Wait for call 0from

above

Wait for

ACK1

rdt_rcv(rcvpkt)


sender receiver

rcv pkt1

rcv pkt0

send ack0

send ack1

send ack0

rcv ack0

send pkt0

send pkt1

rcv ack1

send pkt0rcv pkt0

pkt0

pkt0

pkt1

ack1

ack0

ack0

(a) no loss

sender receiver

rcv pkt1

rcv pkt0

send ack0

send ack1

send ack0

rcv ack0

send pkt0

send pkt1

rcv ack1

send pkt0rcv pkt0

pkt0

pkt0

ack1

ack0

ack0

(b) packet loss

pkt1X

loss

pkt1timeout

resend pkt1

rdt30 in action


rdt30 in action

rcv pkt1send ack1

(detect duplicate)

pkt1

sender receiver

rcv pkt1

rcv pkt0

send ack0

send ack1

send ack0

rcv ack0

send pkt0

send pkt1

rcv ack1

send pkt0rcv pkt0

pkt0

pkt0

ack1

ack0

ack0

(c) ACK loss

ack1X

loss

pkt1timeout

resend pkt1

rcv pkt1send ack1

(detect duplicate)

pkt1

sender receiver

rcv pkt1

send ack0rcv ack0

send pkt1

send pkt0rcv pkt0

pkt0

ack0


pkt1timeout

resend pkt1

ack1

send ack1

send pkt0rcv ack1

pkt0

ack1

ack0






packet


U sender =

008 30008

= 000027 L R RTT + L R

=



Dtrans = LR





sender receiver

RTT




U sender =

008 30008

= 000027 L R RTT + L R

=








RTT






U sender =

0024 30008

= 000081 3L R RTT + L R

=










ack for each packet







window




timeout

rdt_send(data)







base=1nextseqnum=1






Wait







GBN in action


(wait)

sender receiver



rcv ack1 send pkt5


Xloss





0 1 2 3 4 5 6 7 8

sender window (N=4)

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8










Selective repeat



timerACK(n) in








receiver




(wait)

sender receiver



rcv ack1 send pkt5


Xloss




record ack3 arrived

0 1 2 3 4 5 6 7 8

sender window (N=4)

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8







0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2

pkt0pkt1pkt2

0 1 2 3 0 1 2 pkt0


0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2XXX


0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2

pkt0pkt1pkt2

0 1 2 3 0 1 2pkt0

0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2


0 1 2 3 0 1 2 pkt3

(a) no problem















control









overwhelm receiver









32 bits

applicationdata

(variable length)


receive window


lennot

used



ACK ACK valid



commands)



Internetchecksum

(as in UDP)








checksum

rwndurg pointer


A

sent ACKed



not usable

window sizeN




checksum

rwndurg pointer





host ACKsreceipt




Host BHost A



Seq=43 ACK=80














100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106time (seconnds)

RTT

(mill

iseco

nds)






T (m

illise

cond

s)



time (seconds)






(typically = 025)













control









congestion control















waitfor

event



start timer



start timer

timeout






lost ACK scenario

Host BHost A


ACK=100


Xtimeo

ut

ACK=100

premature timeout

Host BHost A


ACK=100


timeo

ut

ACK=120


ACK=120

SendBase=100

SendBase=120

SendBase=120

SendBase=92



X

cumulative ACK

Host BHost A


ACK=100


timeo

ut


ACK=120



event at receiver





TCP receiver action














TCP fast retransmit



X


Host BHost A


ACK=100

timeo

ut ACK=100

ACK=100ACK=100

TCP fast retransmit












control



process


TCPcode

IPcode

applicationOS





from sender


flow control


TCP flow control

buffered data


RcvBuffer


















control








application

network




application

network








2-way handshake

Letrsquos talk

OKESTAB

ESTAB


ESTABacc_conn(x)





ESTAB

req_conn(x)


client terminates

serverforgets x



ESTAB

req_conn(x)

data(x+1)

retransmitdata(x+1)

acceptdata(x+1)

choose xreq_conn(x)

ESTAB

ESTAB

acc_conn(x)

client terminates

ESTAB

choose xreq_conn(x)

ESTABacc_conn(x)



forgets x


TCP 3-way handshake

SYNbit=1 Seq=x


ESTAB



ACKbit=1 ACKnum=y+1




SYNSENT

ESTAB

SYN RCVD

client stateLISTEN

server stateLISTEN



closed

listen

SYNrcvd

SYNsent

ESTAB


SYN(seq=x)











FIN_WAIT_2

CLOSE_WAIT

FINbit=1 seq=y

ACKbit=1 ACKnum=y+1


close

can stillsend data


LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2max

segment lifetime

CLOSED



clientSocketclose()











control





a top-10 problem








Host A

original data in

Host B

throughput out

R2

R2

out

in R2de

lay








Host A

in original data

Host B


lsquo








free buffer space

R2

R2

out

in


Host B

A




no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







rsquo increase


Host A out


Host B

Host CHost D


retransmitted data







C2

C2

out

inrsquo










control





loss

cwnd

TCP

send

er

cong

estio

n w

indo

w s

ize


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwndRTT

bytessec






Host A

RTT

Host B

time



















cwnd gt ssthresh

congestionavoidance



new ACK


fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


WRTT bytessec










TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R






















linkphysical


linkphysical

ECN=00 ECN=11

ECE=1

IP datagram

TCP ACK segment






bull UDPbull TCP

next leaving the





transport

application

physicallink

network

P3transport

application

physicallink

transport

application

physicallink

network

P2



host IP address

A

host IP address

C

server IP

address B

network

P3



P4

threaded server










control













error recovery


UDP segment header


32 bits

applicationdata

(payload)

UDP segment format

length checksum


including header





why is there a UDP


UDP checksum














1 1 1 1 0 0 1 1 0 0 1 1 0 0 1 1 01 1 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1

1 1 0 1 1 1 0 1 1 1 0 1 1 1 0 1 1

1 1 0 1 1 1 0 1 1 1 0 1 1 1 1 0 01 0 1 0 0 0 1 0 0 0 1 0 0 0 0 1 1

wraparound

sumchecksum












control















sendside

receiveside










sender receiver

state1

state2




eventactions







udt_send(packet)


Wait for call from

below

rdt_rcv(packet)

sender receiver







gtsender









sender









udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

belowsender









udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)








udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)














above


rdt_send(data)




rdt_send(data)


udt_send(sndpkt)



Wait forcall 1 from

above




































above


rdt_send(data)

udt_send(sndpkt)


isACK(rcvpkt1) )


Wait for ACK

0sender FSMfragment





has_seq1(rcvpkt))


fragment













rdt_send(data)

Wait for

ACK0



above


rdt_send(data)






timeout


timeout

rdt_rcv(rcvpkt)

Wait for call 0from

above

Wait for

ACK1

rdt_rcv(rcvpkt)


sender receiver

rcv pkt1

rcv pkt0

send ack0

send ack1

send ack0

rcv ack0

send pkt0

send pkt1

rcv ack1

send pkt0rcv pkt0

pkt0

pkt0

pkt1

ack1

ack0

ack0

(a) no loss

sender receiver

rcv pkt1

rcv pkt0

send ack0

send ack1

send ack0

rcv ack0

send pkt0

send pkt1

rcv ack1

send pkt0rcv pkt0

pkt0

pkt0

ack1

ack0

ack0

(b) packet loss

pkt1X

loss

pkt1timeout

resend pkt1

rdt30 in action


rdt30 in action

rcv pkt1send ack1

(detect duplicate)

pkt1

sender receiver

rcv pkt1

rcv pkt0

send ack0

send ack1

send ack0

rcv ack0

send pkt0

send pkt1

rcv ack1

send pkt0rcv pkt0

pkt0

pkt0

ack1

ack0

ack0

(c) ACK loss

ack1X

loss

pkt1timeout

resend pkt1

rcv pkt1send ack1

(detect duplicate)

pkt1

sender receiver

rcv pkt1

send ack0rcv ack0

send pkt1

send pkt0rcv pkt0

pkt0

ack0


pkt1timeout

resend pkt1

ack1

send ack1

send pkt0rcv ack1

pkt0

ack1

ack0






packet


U sender =

008 30008

= 000027 L R RTT + L R

=



Dtrans = LR





sender receiver

RTT




U sender =

008 30008

= 000027 L R RTT + L R

=








RTT






U sender =

0024 30008

= 000081 3L R RTT + L R

=










ack for each packet







window




timeout

rdt_send(data)







base=1nextseqnum=1






Wait







GBN in action


(wait)

sender receiver



rcv ack1 send pkt5


Xloss





0 1 2 3 4 5 6 7 8

sender window (N=4)

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8










Selective repeat



timerACK(n) in








receiver




(wait)

sender receiver



rcv ack1 send pkt5


Xloss




record ack3 arrived

0 1 2 3 4 5 6 7 8

sender window (N=4)

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8







0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2

pkt0pkt1pkt2

0 1 2 3 0 1 2 pkt0


0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2XXX


0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2

pkt0pkt1pkt2

0 1 2 3 0 1 2pkt0

0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2


0 1 2 3 0 1 2 pkt3

(a) no problem















control









overwhelm receiver









32 bits

applicationdata

(variable length)


receive window


lennot

used



ACK ACK valid



commands)



Internetchecksum

(as in UDP)








checksum

rwndurg pointer


A

sent ACKed



not usable

window sizeN




checksum

rwndurg pointer





host ACKsreceipt




Host BHost A



Seq=43 ACK=80














100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106time (seconnds)

RTT

(mill

iseco

nds)






T (m

illise

cond

s)



time (seconds)






(typically = 025)













control









congestion control















waitfor

event



start timer



start timer

timeout






lost ACK scenario

Host BHost A


ACK=100


Xtimeo

ut

ACK=100

premature timeout

Host BHost A


ACK=100


timeo

ut

ACK=120


ACK=120

SendBase=100

SendBase=120

SendBase=120

SendBase=92



X

cumulative ACK

Host BHost A


ACK=100


timeo

ut


ACK=120



event at receiver





TCP receiver action














TCP fast retransmit



X


Host BHost A


ACK=100

timeo

ut ACK=100

ACK=100ACK=100

TCP fast retransmit












control



process


TCPcode

IPcode

applicationOS





from sender


flow control


TCP flow control

buffered data


RcvBuffer


















control








application

network




application

network








2-way handshake

Letrsquos talk

OKESTAB

ESTAB


ESTABacc_conn(x)





ESTAB

req_conn(x)


client terminates

serverforgets x



ESTAB

req_conn(x)

data(x+1)

retransmitdata(x+1)

acceptdata(x+1)

choose xreq_conn(x)

ESTAB

ESTAB

acc_conn(x)

client terminates

ESTAB

choose xreq_conn(x)

ESTABacc_conn(x)



forgets x


TCP 3-way handshake

SYNbit=1 Seq=x


ESTAB



ACKbit=1 ACKnum=y+1




SYNSENT

ESTAB

SYN RCVD

client stateLISTEN

server stateLISTEN



closed

listen

SYNrcvd

SYNsent

ESTAB


SYN(seq=x)











FIN_WAIT_2

CLOSE_WAIT

FINbit=1 seq=y

ACKbit=1 ACKnum=y+1


close

can stillsend data


LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2max

segment lifetime

CLOSED



clientSocketclose()











control





a top-10 problem








Host A

original data in

Host B

throughput out

R2

R2

out

in R2de

lay








Host A

in original data

Host B


lsquo








free buffer space

R2

R2

out

in


Host B

A




no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







rsquo increase


Host A out


Host B

Host CHost D


retransmitted data







C2

C2

out

inrsquo










control





loss

cwnd

TCP

send

er

cong

estio

n w

indo

w s

ize


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwndRTT

bytessec






Host A

RTT

Host B

time



















cwnd gt ssthresh

congestionavoidance



new ACK


fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


WRTT bytessec










TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R






















linkphysical


linkphysical

ECN=00 ECN=11

ECE=1

IP datagram

TCP ACK segment






bull UDPbull TCP

next leaving the












control













error recovery


UDP segment header


32 bits

applicationdata

(payload)

UDP segment format

length checksum


including header





why is there a UDP


UDP checksum














1 1 1 1 0 0 1 1 0 0 1 1 0 0 1 1 01 1 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1

1 1 0 1 1 1 0 1 1 1 0 1 1 1 0 1 1

1 1 0 1 1 1 0 1 1 1 0 1 1 1 1 0 01 0 1 0 0 0 1 0 0 0 1 0 0 0 0 1 1

wraparound

sumchecksum












control















sendside

receiveside










sender receiver

state1

state2




eventactions







udt_send(packet)


Wait for call from

below

rdt_rcv(packet)

sender receiver







gtsender









sender









udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

belowsender









udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)








udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)














above


rdt_send(data)




rdt_send(data)


udt_send(sndpkt)



Wait forcall 1 from

above




































above


rdt_send(data)

udt_send(sndpkt)


isACK(rcvpkt1) )


Wait for ACK

0sender FSMfragment





has_seq1(rcvpkt))


fragment













rdt_send(data)

Wait for

ACK0



above


rdt_send(data)






timeout


timeout

rdt_rcv(rcvpkt)

Wait for call 0from

above

Wait for

ACK1

rdt_rcv(rcvpkt)


sender receiver

rcv pkt1

rcv pkt0

send ack0

send ack1

send ack0

rcv ack0

send pkt0

send pkt1

rcv ack1

send pkt0rcv pkt0

pkt0

pkt0

pkt1

ack1

ack0

ack0

(a) no loss

sender receiver

rcv pkt1

rcv pkt0

send ack0

send ack1

send ack0

rcv ack0

send pkt0

send pkt1

rcv ack1

send pkt0rcv pkt0

pkt0

pkt0

ack1

ack0

ack0

(b) packet loss

pkt1X

loss

pkt1timeout

resend pkt1

rdt30 in action


rdt30 in action

rcv pkt1send ack1

(detect duplicate)

pkt1

sender receiver

rcv pkt1

rcv pkt0

send ack0

send ack1

send ack0

rcv ack0

send pkt0

send pkt1

rcv ack1

send pkt0rcv pkt0

pkt0

pkt0

ack1

ack0

ack0

(c) ACK loss

ack1X

loss

pkt1timeout

resend pkt1

rcv pkt1send ack1

(detect duplicate)

pkt1

sender receiver

rcv pkt1

send ack0rcv ack0

send pkt1

send pkt0rcv pkt0

pkt0

ack0


pkt1timeout

resend pkt1

ack1

send ack1

send pkt0rcv ack1

pkt0

ack1

ack0






packet


U sender =

008 30008

= 000027 L R RTT + L R

=



Dtrans = LR





sender receiver

RTT




U sender =

008 30008

= 000027 L R RTT + L R

=








RTT






U sender =

0024 30008

= 000081 3L R RTT + L R

=










ack for each packet







window




timeout

rdt_send(data)







base=1nextseqnum=1






Wait







GBN in action


(wait)

sender receiver



rcv ack1 send pkt5


Xloss





0 1 2 3 4 5 6 7 8

sender window (N=4)

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8










Selective repeat



timerACK(n) in








receiver




(wait)

sender receiver



rcv ack1 send pkt5


Xloss




record ack3 arrived

0 1 2 3 4 5 6 7 8

sender window (N=4)

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8







0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2

pkt0pkt1pkt2

0 1 2 3 0 1 2 pkt0


0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2XXX


0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2

pkt0pkt1pkt2

0 1 2 3 0 1 2pkt0

0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2


0 1 2 3 0 1 2 pkt3

(a) no problem















control









overwhelm receiver









32 bits

applicationdata

(variable length)


receive window


lennot

used



ACK ACK valid



commands)



Internetchecksum

(as in UDP)








checksum

rwndurg pointer


A

sent ACKed



not usable

window sizeN




checksum

rwndurg pointer





host ACKsreceipt




Host BHost A



Seq=43 ACK=80














100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106time (seconnds)

RTT

(mill

iseco

nds)






T (m

illise

cond

s)



time (seconds)






(typically = 025)













control









congestion control















waitfor

event



start timer



start timer

timeout






lost ACK scenario

Host BHost A


ACK=100


Xtimeo

ut

ACK=100

premature timeout

Host BHost A


ACK=100


timeo

ut

ACK=120


ACK=120

SendBase=100

SendBase=120

SendBase=120

SendBase=92



X

cumulative ACK

Host BHost A


ACK=100


timeo

ut


ACK=120



event at receiver





TCP receiver action














TCP fast retransmit



X


Host BHost A


ACK=100

timeo

ut ACK=100

ACK=100ACK=100

TCP fast retransmit












control



process


TCPcode

IPcode

applicationOS





from sender


flow control


TCP flow control

buffered data


RcvBuffer


















control








application

network




application

network








2-way handshake

Letrsquos talk

OKESTAB

ESTAB


ESTABacc_conn(x)





ESTAB

req_conn(x)


client terminates

serverforgets x



ESTAB

req_conn(x)

data(x+1)

retransmitdata(x+1)

acceptdata(x+1)

choose xreq_conn(x)

ESTAB

ESTAB

acc_conn(x)

client terminates

ESTAB

choose xreq_conn(x)

ESTABacc_conn(x)



forgets x


TCP 3-way handshake

SYNbit=1 Seq=x


ESTAB



ACKbit=1 ACKnum=y+1




SYNSENT

ESTAB

SYN RCVD

client stateLISTEN

server stateLISTEN



closed

listen

SYNrcvd

SYNsent

ESTAB


SYN(seq=x)











FIN_WAIT_2

CLOSE_WAIT

FINbit=1 seq=y

ACKbit=1 ACKnum=y+1


close

can stillsend data


LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2max

segment lifetime

CLOSED



clientSocketclose()











control





a top-10 problem








Host A

original data in

Host B

throughput out

R2

R2

out

in R2de

lay








Host A

in original data

Host B


lsquo








free buffer space

R2

R2

out

in


Host B

A




no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







rsquo increase


Host A out


Host B

Host CHost D


retransmitted data







C2

C2

out

inrsquo










control





loss

cwnd

TCP

send

er

cong

estio

n w

indo

w s

ize


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwndRTT

bytessec






Host A

RTT

Host B

time



















cwnd gt ssthresh

congestionavoidance



new ACK


fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


WRTT bytessec










TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R






















linkphysical


linkphysical

ECN=00 ECN=11

ECE=1

IP datagram

TCP ACK segment






bull UDPbull TCP

next leaving the















error recovery


UDP segment header


32 bits

applicationdata

(payload)

UDP segment format

length checksum


including header





why is there a UDP


UDP checksum














1 1 1 1 0 0 1 1 0 0 1 1 0 0 1 1 01 1 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1

1 1 0 1 1 1 0 1 1 1 0 1 1 1 0 1 1

1 1 0 1 1 1 0 1 1 1 0 1 1 1 1 0 01 0 1 0 0 0 1 0 0 0 1 0 0 0 0 1 1

wraparound

sumchecksum












control















sendside

receiveside










sender receiver

state1

state2




eventactions







udt_send(packet)


Wait for call from

below

rdt_rcv(packet)

sender receiver







gtsender









sender









udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

belowsender









udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)








udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)














above


rdt_send(data)




rdt_send(data)


udt_send(sndpkt)



Wait forcall 1 from

above




































above


rdt_send(data)

udt_send(sndpkt)


isACK(rcvpkt1) )


Wait for ACK

0sender FSMfragment





has_seq1(rcvpkt))


fragment













rdt_send(data)

Wait for

ACK0



above


rdt_send(data)






timeout


timeout

rdt_rcv(rcvpkt)

Wait for call 0from

above

Wait for

ACK1

rdt_rcv(rcvpkt)


sender receiver

rcv pkt1

rcv pkt0

send ack0

send ack1

send ack0

rcv ack0

send pkt0

send pkt1

rcv ack1

send pkt0rcv pkt0

pkt0

pkt0

pkt1

ack1

ack0

ack0

(a) no loss

sender receiver

rcv pkt1

rcv pkt0

send ack0

send ack1

send ack0

rcv ack0

send pkt0

send pkt1

rcv ack1

send pkt0rcv pkt0

pkt0

pkt0

ack1

ack0

ack0

(b) packet loss

pkt1X

loss

pkt1timeout

resend pkt1

rdt30 in action


rdt30 in action

rcv pkt1send ack1

(detect duplicate)

pkt1

sender receiver

rcv pkt1

rcv pkt0

send ack0

send ack1

send ack0

rcv ack0

send pkt0

send pkt1

rcv ack1

send pkt0rcv pkt0

pkt0

pkt0

ack1

ack0

ack0

(c) ACK loss

ack1X

loss

pkt1timeout

resend pkt1

rcv pkt1send ack1

(detect duplicate)

pkt1

sender receiver

rcv pkt1

send ack0rcv ack0

send pkt1

send pkt0rcv pkt0

pkt0

ack0


pkt1timeout

resend pkt1

ack1

send ack1

send pkt0rcv ack1

pkt0

ack1

ack0






packet


U sender =

008 30008

= 000027 L R RTT + L R

=



Dtrans = LR





sender receiver

RTT




U sender =

008 30008

= 000027 L R RTT + L R

=








RTT






U sender =

0024 30008

= 000081 3L R RTT + L R

=










ack for each packet







window




timeout

rdt_send(data)







base=1nextseqnum=1






Wait







GBN in action


(wait)

sender receiver



rcv ack1 send pkt5


Xloss





0 1 2 3 4 5 6 7 8

sender window (N=4)

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8










Selective repeat



timerACK(n) in








receiver




(wait)

sender receiver



rcv ack1 send pkt5


Xloss




record ack3 arrived

0 1 2 3 4 5 6 7 8

sender window (N=4)

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8







0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2

pkt0pkt1pkt2

0 1 2 3 0 1 2 pkt0


0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2XXX


0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2

pkt0pkt1pkt2

0 1 2 3 0 1 2pkt0

0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2


0 1 2 3 0 1 2 pkt3

(a) no problem















control









overwhelm receiver









32 bits

applicationdata

(variable length)


receive window


lennot

used



ACK ACK valid



commands)



Internetchecksum

(as in UDP)








checksum

rwndurg pointer


A

sent ACKed



not usable

window sizeN




checksum

rwndurg pointer





host ACKsreceipt




Host BHost A



Seq=43 ACK=80














100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106time (seconnds)

RTT

(mill

iseco

nds)






T (m

illise

cond

s)



time (seconds)






(typically = 025)













control









congestion control















waitfor

event



start timer



start timer

timeout






lost ACK scenario

Host BHost A


ACK=100


Xtimeo

ut

ACK=100

premature timeout

Host BHost A


ACK=100


timeo

ut

ACK=120


ACK=120

SendBase=100

SendBase=120

SendBase=120

SendBase=92



X

cumulative ACK

Host BHost A


ACK=100


timeo

ut


ACK=120



event at receiver





TCP receiver action














TCP fast retransmit



X


Host BHost A


ACK=100

timeo

ut ACK=100

ACK=100ACK=100

TCP fast retransmit












control



process


TCPcode

IPcode

applicationOS





from sender


flow control


TCP flow control

buffered data


RcvBuffer


















control








application

network




application

network








2-way handshake

Letrsquos talk

OKESTAB

ESTAB


ESTABacc_conn(x)





ESTAB

req_conn(x)


client terminates

serverforgets x



ESTAB

req_conn(x)

data(x+1)

retransmitdata(x+1)

acceptdata(x+1)

choose xreq_conn(x)

ESTAB

ESTAB

acc_conn(x)

client terminates

ESTAB

choose xreq_conn(x)

ESTABacc_conn(x)



forgets x


TCP 3-way handshake

SYNbit=1 Seq=x


ESTAB



ACKbit=1 ACKnum=y+1




SYNSENT

ESTAB

SYN RCVD

client stateLISTEN

server stateLISTEN



closed

listen

SYNrcvd

SYNsent

ESTAB


SYN(seq=x)











FIN_WAIT_2

CLOSE_WAIT

FINbit=1 seq=y

ACKbit=1 ACKnum=y+1


close

can stillsend data


LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2max

segment lifetime

CLOSED



clientSocketclose()











control





a top-10 problem








Host A

original data in

Host B

throughput out

R2

R2

out

in R2de

lay








Host A

in original data

Host B


lsquo








free buffer space

R2

R2

out

in


Host B

A




no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







rsquo increase


Host A out


Host B

Host CHost D


retransmitted data







C2

C2

out

inrsquo










control





loss

cwnd

TCP

send

er

cong

estio

n w

indo

w s

ize


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwndRTT

bytessec






Host A

RTT

Host B

time



















cwnd gt ssthresh

congestionavoidance



new ACK


fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


WRTT bytessec










TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R






















linkphysical


linkphysical

ECN=00 ECN=11

ECE=1

IP datagram

TCP ACK segment






bull UDPbull TCP

next leaving the




UDP segment header


32 bits

applicationdata

(payload)

UDP segment format

length checksum


including header





why is there a UDP


UDP checksum














1 1 1 1 0 0 1 1 0 0 1 1 0 0 1 1 01 1 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1

1 1 0 1 1 1 0 1 1 1 0 1 1 1 0 1 1

1 1 0 1 1 1 0 1 1 1 0 1 1 1 1 0 01 0 1 0 0 0 1 0 0 0 1 0 0 0 0 1 1

wraparound

sumchecksum












control















sendside

receiveside










sender receiver

state1

state2




eventactions







udt_send(packet)


Wait for call from

below

rdt_rcv(packet)

sender receiver







gtsender









sender









udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

belowsender









udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)








udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)














above


rdt_send(data)




rdt_send(data)


udt_send(sndpkt)



Wait forcall 1 from

above




































above


rdt_send(data)

udt_send(sndpkt)


isACK(rcvpkt1) )


Wait for ACK

0sender FSMfragment





has_seq1(rcvpkt))


fragment













rdt_send(data)

Wait for

ACK0



above


rdt_send(data)






timeout


timeout

rdt_rcv(rcvpkt)

Wait for call 0from

above

Wait for

ACK1

rdt_rcv(rcvpkt)


sender receiver

rcv pkt1

rcv pkt0

send ack0

send ack1

send ack0

rcv ack0

send pkt0

send pkt1

rcv ack1

send pkt0rcv pkt0

pkt0

pkt0

pkt1

ack1

ack0

ack0

(a) no loss

sender receiver

rcv pkt1

rcv pkt0

send ack0

send ack1

send ack0

rcv ack0

send pkt0

send pkt1

rcv ack1

send pkt0rcv pkt0

pkt0

pkt0

ack1

ack0

ack0

(b) packet loss

pkt1X

loss

pkt1timeout

resend pkt1

rdt30 in action


rdt30 in action

rcv pkt1send ack1

(detect duplicate)

pkt1

sender receiver

rcv pkt1

rcv pkt0

send ack0

send ack1

send ack0

rcv ack0

send pkt0

send pkt1

rcv ack1

send pkt0rcv pkt0

pkt0

pkt0

ack1

ack0

ack0

(c) ACK loss

ack1X

loss

pkt1timeout

resend pkt1

rcv pkt1send ack1

(detect duplicate)

pkt1

sender receiver

rcv pkt1

send ack0rcv ack0

send pkt1

send pkt0rcv pkt0

pkt0

ack0


pkt1timeout

resend pkt1

ack1

send ack1

send pkt0rcv ack1

pkt0

ack1

ack0






packet


U sender =

008 30008

= 000027 L R RTT + L R

=



Dtrans = LR





sender receiver

RTT




U sender =

008 30008

= 000027 L R RTT + L R

=








RTT






U sender =

0024 30008

= 000081 3L R RTT + L R

=










ack for each packet







window




timeout

rdt_send(data)







base=1nextseqnum=1






Wait







GBN in action


(wait)

sender receiver



rcv ack1 send pkt5


Xloss





0 1 2 3 4 5 6 7 8

sender window (N=4)

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8










Selective repeat



timerACK(n) in








receiver




(wait)

sender receiver



rcv ack1 send pkt5


Xloss




record ack3 arrived

0 1 2 3 4 5 6 7 8

sender window (N=4)

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8







0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2

pkt0pkt1pkt2

0 1 2 3 0 1 2 pkt0


0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2XXX


0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2

pkt0pkt1pkt2

0 1 2 3 0 1 2pkt0

0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2


0 1 2 3 0 1 2 pkt3

(a) no problem















control









overwhelm receiver









32 bits

applicationdata

(variable length)


receive window


lennot

used



ACK ACK valid



commands)



Internetchecksum

(as in UDP)








checksum

rwndurg pointer


A

sent ACKed



not usable

window sizeN




checksum

rwndurg pointer





host ACKsreceipt




Host BHost A



Seq=43 ACK=80














100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106time (seconnds)

RTT

(mill

iseco

nds)






T (m

illise

cond

s)



time (seconds)






(typically = 025)













control









congestion control















waitfor

event



start timer



start timer

timeout






lost ACK scenario

Host BHost A


ACK=100


Xtimeo

ut

ACK=100

premature timeout

Host BHost A


ACK=100


timeo

ut

ACK=120


ACK=120

SendBase=100

SendBase=120

SendBase=120

SendBase=92



X

cumulative ACK

Host BHost A


ACK=100


timeo

ut


ACK=120



event at receiver





TCP receiver action














TCP fast retransmit



X


Host BHost A


ACK=100

timeo

ut ACK=100

ACK=100ACK=100

TCP fast retransmit












control



process


TCPcode

IPcode

applicationOS





from sender


flow control


TCP flow control

buffered data


RcvBuffer


















control








application

network




application

network








2-way handshake

Letrsquos talk

OKESTAB

ESTAB


ESTABacc_conn(x)





ESTAB

req_conn(x)


client terminates

serverforgets x



ESTAB

req_conn(x)

data(x+1)

retransmitdata(x+1)

acceptdata(x+1)

choose xreq_conn(x)

ESTAB

ESTAB

acc_conn(x)

client terminates

ESTAB

choose xreq_conn(x)

ESTABacc_conn(x)



forgets x


TCP 3-way handshake

SYNbit=1 Seq=x


ESTAB



ACKbit=1 ACKnum=y+1




SYNSENT

ESTAB

SYN RCVD

client stateLISTEN

server stateLISTEN



closed

listen

SYNrcvd

SYNsent

ESTAB


SYN(seq=x)











FIN_WAIT_2

CLOSE_WAIT

FINbit=1 seq=y

ACKbit=1 ACKnum=y+1


close

can stillsend data


LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2max

segment lifetime

CLOSED



clientSocketclose()











control





a top-10 problem








Host A

original data in

Host B

throughput out

R2

R2

out

in R2de

lay








Host A

in original data

Host B


lsquo








free buffer space

R2

R2

out

in


Host B

A




no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







rsquo increase


Host A out


Host B

Host CHost D


retransmitted data







C2

C2

out

inrsquo










control





loss

cwnd

TCP

send

er

cong

estio

n w

indo

w s

ize


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwndRTT

bytessec






Host A

RTT

Host B

time



















cwnd gt ssthresh

congestionavoidance



new ACK


fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


WRTT bytessec










TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R






















linkphysical


linkphysical

ECN=00 ECN=11

ECE=1

IP datagram

TCP ACK segment






bull UDPbull TCP

next leaving the




UDP checksum














1 1 1 1 0 0 1 1 0 0 1 1 0 0 1 1 01 1 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1

1 1 0 1 1 1 0 1 1 1 0 1 1 1 0 1 1

1 1 0 1 1 1 0 1 1 1 0 1 1 1 1 0 01 0 1 0 0 0 1 0 0 0 1 0 0 0 0 1 1

wraparound

sumchecksum












control















sendside

receiveside










sender receiver

state1

state2




eventactions







udt_send(packet)


Wait for call from

below

rdt_rcv(packet)

sender receiver







gtsender









sender









udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

belowsender









udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)








udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)














above


rdt_send(data)




rdt_send(data)


udt_send(sndpkt)



Wait forcall 1 from

above




































above


rdt_send(data)

udt_send(sndpkt)


isACK(rcvpkt1) )


Wait for ACK

0sender FSMfragment





has_seq1(rcvpkt))


fragment













rdt_send(data)

Wait for

ACK0



above


rdt_send(data)






timeout


timeout

rdt_rcv(rcvpkt)

Wait for call 0from

above

Wait for

ACK1

rdt_rcv(rcvpkt)


sender receiver

rcv pkt1

rcv pkt0

send ack0

send ack1

send ack0

rcv ack0

send pkt0

send pkt1

rcv ack1

send pkt0rcv pkt0

pkt0

pkt0

pkt1

ack1

ack0

ack0

(a) no loss

sender receiver

rcv pkt1

rcv pkt0

send ack0

send ack1

send ack0

rcv ack0

send pkt0

send pkt1

rcv ack1

send pkt0rcv pkt0

pkt0

pkt0

ack1

ack0

ack0

(b) packet loss

pkt1X

loss

pkt1timeout

resend pkt1

rdt30 in action


rdt30 in action

rcv pkt1send ack1

(detect duplicate)

pkt1

sender receiver

rcv pkt1

rcv pkt0

send ack0

send ack1

send ack0

rcv ack0

send pkt0

send pkt1

rcv ack1

send pkt0rcv pkt0

pkt0

pkt0

ack1

ack0

ack0

(c) ACK loss

ack1X

loss

pkt1timeout

resend pkt1

rcv pkt1send ack1

(detect duplicate)

pkt1

sender receiver

rcv pkt1

send ack0rcv ack0

send pkt1

send pkt0rcv pkt0

pkt0

ack0


pkt1timeout

resend pkt1

ack1

send ack1

send pkt0rcv ack1

pkt0

ack1

ack0






packet


U sender =

008 30008

= 000027 L R RTT + L R

=



Dtrans = LR





sender receiver

RTT




U sender =

008 30008

= 000027 L R RTT + L R

=








RTT






U sender =

0024 30008

= 000081 3L R RTT + L R

=










ack for each packet







window




timeout

rdt_send(data)







base=1nextseqnum=1






Wait







GBN in action


(wait)

sender receiver



rcv ack1 send pkt5


Xloss





0 1 2 3 4 5 6 7 8

sender window (N=4)

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8










Selective repeat



timerACK(n) in








receiver




(wait)

sender receiver



rcv ack1 send pkt5


Xloss




record ack3 arrived

0 1 2 3 4 5 6 7 8

sender window (N=4)

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8







0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2

pkt0pkt1pkt2

0 1 2 3 0 1 2 pkt0


0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2XXX


0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2

pkt0pkt1pkt2

0 1 2 3 0 1 2pkt0

0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2


0 1 2 3 0 1 2 pkt3

(a) no problem















control









overwhelm receiver









32 bits

applicationdata

(variable length)


receive window


lennot

used



ACK ACK valid



commands)



Internetchecksum

(as in UDP)








checksum

rwndurg pointer


A

sent ACKed



not usable

window sizeN




checksum

rwndurg pointer





host ACKsreceipt




Host BHost A



Seq=43 ACK=80














100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106time (seconnds)

RTT

(mill

iseco

nds)






T (m

illise

cond

s)



time (seconds)






(typically = 025)













control









congestion control















waitfor

event



start timer



start timer

timeout






lost ACK scenario

Host BHost A


ACK=100


Xtimeo

ut

ACK=100

premature timeout

Host BHost A


ACK=100


timeo

ut

ACK=120


ACK=120

SendBase=100

SendBase=120

SendBase=120

SendBase=92



X

cumulative ACK

Host BHost A


ACK=100


timeo

ut


ACK=120



event at receiver





TCP receiver action














TCP fast retransmit



X


Host BHost A


ACK=100

timeo

ut ACK=100

ACK=100ACK=100

TCP fast retransmit












control



process


TCPcode

IPcode

applicationOS





from sender


flow control


TCP flow control

buffered data


RcvBuffer


















control








application

network




application

network








2-way handshake

Letrsquos talk

OKESTAB

ESTAB


ESTABacc_conn(x)





ESTAB

req_conn(x)


client terminates

serverforgets x



ESTAB

req_conn(x)

data(x+1)

retransmitdata(x+1)

acceptdata(x+1)

choose xreq_conn(x)

ESTAB

ESTAB

acc_conn(x)

client terminates

ESTAB

choose xreq_conn(x)

ESTABacc_conn(x)



forgets x


TCP 3-way handshake

SYNbit=1 Seq=x


ESTAB



ACKbit=1 ACKnum=y+1




SYNSENT

ESTAB

SYN RCVD

client stateLISTEN

server stateLISTEN



closed

listen

SYNrcvd

SYNsent

ESTAB


SYN(seq=x)











FIN_WAIT_2

CLOSE_WAIT

FINbit=1 seq=y

ACKbit=1 ACKnum=y+1


close

can stillsend data


LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2max

segment lifetime

CLOSED



clientSocketclose()











control





a top-10 problem








Host A

original data in

Host B

throughput out

R2

R2

out

in R2de

lay








Host A

in original data

Host B


lsquo








free buffer space

R2

R2

out

in


Host B

A




no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







rsquo increase


Host A out


Host B

Host CHost D


retransmitted data







C2

C2

out

inrsquo










control





loss

cwnd

TCP

send

er

cong

estio

n w

indo

w s

ize


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwndRTT

bytessec






Host A

RTT

Host B

time



















cwnd gt ssthresh

congestionavoidance



new ACK


fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


WRTT bytessec










TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R






















linkphysical


linkphysical

ECN=00 ECN=11

ECE=1

IP datagram

TCP ACK segment






bull UDPbull TCP

next leaving the






1 1 1 1 0 0 1 1 0 0 1 1 0 0 1 1 01 1 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1

1 1 0 1 1 1 0 1 1 1 0 1 1 1 0 1 1

1 1 0 1 1 1 0 1 1 1 0 1 1 1 1 0 01 0 1 0 0 0 1 0 0 0 1 0 0 0 0 1 1

wraparound

sumchecksum












control















sendside

receiveside










sender receiver

state1

state2




eventactions







udt_send(packet)


Wait for call from

below

rdt_rcv(packet)

sender receiver







gtsender









sender









udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

belowsender









udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)








udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)














above


rdt_send(data)




rdt_send(data)


udt_send(sndpkt)



Wait forcall 1 from

above




































above


rdt_send(data)

udt_send(sndpkt)


isACK(rcvpkt1) )


Wait for ACK

0sender FSMfragment





has_seq1(rcvpkt))


fragment













rdt_send(data)

Wait for

ACK0



above


rdt_send(data)






timeout


timeout

rdt_rcv(rcvpkt)

Wait for call 0from

above

Wait for

ACK1

rdt_rcv(rcvpkt)


sender receiver

rcv pkt1

rcv pkt0

send ack0

send ack1

send ack0

rcv ack0

send pkt0

send pkt1

rcv ack1

send pkt0rcv pkt0

pkt0

pkt0

pkt1

ack1

ack0

ack0

(a) no loss

sender receiver

rcv pkt1

rcv pkt0

send ack0

send ack1

send ack0

rcv ack0

send pkt0

send pkt1

rcv ack1

send pkt0rcv pkt0

pkt0

pkt0

ack1

ack0

ack0

(b) packet loss

pkt1X

loss

pkt1timeout

resend pkt1

rdt30 in action


rdt30 in action

rcv pkt1send ack1

(detect duplicate)

pkt1

sender receiver

rcv pkt1

rcv pkt0

send ack0

send ack1

send ack0

rcv ack0

send pkt0

send pkt1

rcv ack1

send pkt0rcv pkt0

pkt0

pkt0

ack1

ack0

ack0

(c) ACK loss

ack1X

loss

pkt1timeout

resend pkt1

rcv pkt1send ack1

(detect duplicate)

pkt1

sender receiver

rcv pkt1

send ack0rcv ack0

send pkt1

send pkt0rcv pkt0

pkt0

ack0


pkt1timeout

resend pkt1

ack1

send ack1

send pkt0rcv ack1

pkt0

ack1

ack0






packet


U sender =

008 30008

= 000027 L R RTT + L R

=



Dtrans = LR





sender receiver

RTT




U sender =

008 30008

= 000027 L R RTT + L R

=








RTT






U sender =

0024 30008

= 000081 3L R RTT + L R

=










ack for each packet







window




timeout

rdt_send(data)







base=1nextseqnum=1






Wait







GBN in action


(wait)

sender receiver



rcv ack1 send pkt5


Xloss





0 1 2 3 4 5 6 7 8

sender window (N=4)

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8










Selective repeat



timerACK(n) in








receiver




(wait)

sender receiver



rcv ack1 send pkt5


Xloss




record ack3 arrived

0 1 2 3 4 5 6 7 8

sender window (N=4)

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8







0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2

pkt0pkt1pkt2

0 1 2 3 0 1 2 pkt0


0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2XXX


0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2

pkt0pkt1pkt2

0 1 2 3 0 1 2pkt0

0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2


0 1 2 3 0 1 2 pkt3

(a) no problem















control









overwhelm receiver









32 bits

applicationdata

(variable length)


receive window


lennot

used



ACK ACK valid



commands)



Internetchecksum

(as in UDP)








checksum

rwndurg pointer


A

sent ACKed



not usable

window sizeN




checksum

rwndurg pointer





host ACKsreceipt




Host BHost A



Seq=43 ACK=80














100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106time (seconnds)

RTT

(mill

iseco

nds)






T (m

illise

cond

s)



time (seconds)






(typically = 025)













control









congestion control















waitfor

event



start timer



start timer

timeout






lost ACK scenario

Host BHost A


ACK=100


Xtimeo

ut

ACK=100

premature timeout

Host BHost A


ACK=100


timeo

ut

ACK=120


ACK=120

SendBase=100

SendBase=120

SendBase=120

SendBase=92



X

cumulative ACK

Host BHost A


ACK=100


timeo

ut


ACK=120



event at receiver





TCP receiver action














TCP fast retransmit



X


Host BHost A


ACK=100

timeo

ut ACK=100

ACK=100ACK=100

TCP fast retransmit












control



process


TCPcode

IPcode

applicationOS





from sender


flow control


TCP flow control

buffered data


RcvBuffer


















control








application

network




application

network








2-way handshake

Letrsquos talk

OKESTAB

ESTAB


ESTABacc_conn(x)





ESTAB

req_conn(x)


client terminates

serverforgets x



ESTAB

req_conn(x)

data(x+1)

retransmitdata(x+1)

acceptdata(x+1)

choose xreq_conn(x)

ESTAB

ESTAB

acc_conn(x)

client terminates

ESTAB

choose xreq_conn(x)

ESTABacc_conn(x)



forgets x


TCP 3-way handshake

SYNbit=1 Seq=x


ESTAB



ACKbit=1 ACKnum=y+1




SYNSENT

ESTAB

SYN RCVD

client stateLISTEN

server stateLISTEN



closed

listen

SYNrcvd

SYNsent

ESTAB


SYN(seq=x)











FIN_WAIT_2

CLOSE_WAIT

FINbit=1 seq=y

ACKbit=1 ACKnum=y+1


close

can stillsend data


LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2max

segment lifetime

CLOSED



clientSocketclose()











control





a top-10 problem








Host A

original data in

Host B

throughput out

R2

R2

out

in R2de

lay








Host A

in original data

Host B


lsquo








free buffer space

R2

R2

out

in


Host B

A




no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







rsquo increase


Host A out


Host B

Host CHost D


retransmitted data







C2

C2

out

inrsquo










control





loss

cwnd

TCP

send

er

cong

estio

n w

indo

w s

ize


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwndRTT

bytessec






Host A

RTT

Host B

time



















cwnd gt ssthresh

congestionavoidance



new ACK


fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


WRTT bytessec










TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R






















linkphysical


linkphysical

ECN=00 ECN=11

ECE=1

IP datagram

TCP ACK segment






bull UDPbull TCP

next leaving the












control















sendside

receiveside










sender receiver

state1

state2




eventactions







udt_send(packet)


Wait for call from

below

rdt_rcv(packet)

sender receiver







gtsender









sender









udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

belowsender









udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)








udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)














above


rdt_send(data)




rdt_send(data)


udt_send(sndpkt)



Wait forcall 1 from

above




































above


rdt_send(data)

udt_send(sndpkt)


isACK(rcvpkt1) )


Wait for ACK

0sender FSMfragment





has_seq1(rcvpkt))


fragment













rdt_send(data)

Wait for

ACK0



above


rdt_send(data)






timeout


timeout

rdt_rcv(rcvpkt)

Wait for call 0from

above

Wait for

ACK1

rdt_rcv(rcvpkt)


sender receiver

rcv pkt1

rcv pkt0

send ack0

send ack1

send ack0

rcv ack0

send pkt0

send pkt1

rcv ack1

send pkt0rcv pkt0

pkt0

pkt0

pkt1

ack1

ack0

ack0

(a) no loss

sender receiver

rcv pkt1

rcv pkt0

send ack0

send ack1

send ack0

rcv ack0

send pkt0

send pkt1

rcv ack1

send pkt0rcv pkt0

pkt0

pkt0

ack1

ack0

ack0

(b) packet loss

pkt1X

loss

pkt1timeout

resend pkt1

rdt30 in action


rdt30 in action

rcv pkt1send ack1

(detect duplicate)

pkt1

sender receiver

rcv pkt1

rcv pkt0

send ack0

send ack1

send ack0

rcv ack0

send pkt0

send pkt1

rcv ack1

send pkt0rcv pkt0

pkt0

pkt0

ack1

ack0

ack0

(c) ACK loss

ack1X

loss

pkt1timeout

resend pkt1

rcv pkt1send ack1

(detect duplicate)

pkt1

sender receiver

rcv pkt1

send ack0rcv ack0

send pkt1

send pkt0rcv pkt0

pkt0

ack0


pkt1timeout

resend pkt1

ack1

send ack1

send pkt0rcv ack1

pkt0

ack1

ack0






packet


U sender =

008 30008

= 000027 L R RTT + L R

=



Dtrans = LR





sender receiver

RTT




U sender =

008 30008

= 000027 L R RTT + L R

=








RTT






U sender =

0024 30008

= 000081 3L R RTT + L R

=










ack for each packet







window




timeout

rdt_send(data)







base=1nextseqnum=1






Wait







GBN in action


(wait)

sender receiver



rcv ack1 send pkt5


Xloss





0 1 2 3 4 5 6 7 8

sender window (N=4)

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8










Selective repeat



timerACK(n) in








receiver




(wait)

sender receiver



rcv ack1 send pkt5


Xloss




record ack3 arrived

0 1 2 3 4 5 6 7 8

sender window (N=4)

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8







0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2

pkt0pkt1pkt2

0 1 2 3 0 1 2 pkt0


0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2XXX


0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2

pkt0pkt1pkt2

0 1 2 3 0 1 2pkt0

0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2


0 1 2 3 0 1 2 pkt3

(a) no problem















control









overwhelm receiver









32 bits

applicationdata

(variable length)


receive window


lennot

used



ACK ACK valid



commands)



Internetchecksum

(as in UDP)








checksum

rwndurg pointer


A

sent ACKed



not usable

window sizeN




checksum

rwndurg pointer





host ACKsreceipt




Host BHost A



Seq=43 ACK=80














100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106time (seconnds)

RTT

(mill

iseco

nds)






T (m

illise

cond

s)



time (seconds)






(typically = 025)













control









congestion control















waitfor

event



start timer



start timer

timeout






lost ACK scenario

Host BHost A


ACK=100


Xtimeo

ut

ACK=100

premature timeout

Host BHost A


ACK=100


timeo

ut

ACK=120


ACK=120

SendBase=100

SendBase=120

SendBase=120

SendBase=92



X

cumulative ACK

Host BHost A


ACK=100


timeo

ut


ACK=120



event at receiver





TCP receiver action














TCP fast retransmit



X


Host BHost A


ACK=100

timeo

ut ACK=100

ACK=100ACK=100

TCP fast retransmit












control



process


TCPcode

IPcode

applicationOS





from sender


flow control


TCP flow control

buffered data


RcvBuffer


















control








application

network




application

network








2-way handshake

Letrsquos talk

OKESTAB

ESTAB


ESTABacc_conn(x)





ESTAB

req_conn(x)


client terminates

serverforgets x



ESTAB

req_conn(x)

data(x+1)

retransmitdata(x+1)

acceptdata(x+1)

choose xreq_conn(x)

ESTAB

ESTAB

acc_conn(x)

client terminates

ESTAB

choose xreq_conn(x)

ESTABacc_conn(x)



forgets x


TCP 3-way handshake

SYNbit=1 Seq=x


ESTAB



ACKbit=1 ACKnum=y+1




SYNSENT

ESTAB

SYN RCVD

client stateLISTEN

server stateLISTEN



closed

listen

SYNrcvd

SYNsent

ESTAB


SYN(seq=x)











FIN_WAIT_2

CLOSE_WAIT

FINbit=1 seq=y

ACKbit=1 ACKnum=y+1


close

can stillsend data


LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2max

segment lifetime

CLOSED



clientSocketclose()











control





a top-10 problem








Host A

original data in

Host B

throughput out

R2

R2

out

in R2de

lay








Host A

in original data

Host B


lsquo








free buffer space

R2

R2

out

in


Host B

A




no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







rsquo increase


Host A out


Host B

Host CHost D


retransmitted data







C2

C2

out

inrsquo










control





loss

cwnd

TCP

send

er

cong

estio

n w

indo

w s

ize


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwndRTT

bytessec






Host A

RTT

Host B

time



















cwnd gt ssthresh

congestionavoidance



new ACK


fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


WRTT bytessec










TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R






















linkphysical


linkphysical

ECN=00 ECN=11

ECE=1

IP datagram

TCP ACK segment






bull UDPbull TCP

next leaving the

















sendside

receiveside










sender receiver

state1

state2




eventactions







udt_send(packet)


Wait for call from

below

rdt_rcv(packet)

sender receiver







gtsender









sender









udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

belowsender









udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)








udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)














above


rdt_send(data)




rdt_send(data)


udt_send(sndpkt)



Wait forcall 1 from

above




































above


rdt_send(data)

udt_send(sndpkt)


isACK(rcvpkt1) )


Wait for ACK

0sender FSMfragment





has_seq1(rcvpkt))


fragment













rdt_send(data)

Wait for

ACK0



above


rdt_send(data)






timeout


timeout

rdt_rcv(rcvpkt)

Wait for call 0from

above

Wait for

ACK1

rdt_rcv(rcvpkt)


sender receiver

rcv pkt1

rcv pkt0

send ack0

send ack1

send ack0

rcv ack0

send pkt0

send pkt1

rcv ack1

send pkt0rcv pkt0

pkt0

pkt0

pkt1

ack1

ack0

ack0

(a) no loss

sender receiver

rcv pkt1

rcv pkt0

send ack0

send ack1

send ack0

rcv ack0

send pkt0

send pkt1

rcv ack1

send pkt0rcv pkt0

pkt0

pkt0

ack1

ack0

ack0

(b) packet loss

pkt1X

loss

pkt1timeout

resend pkt1

rdt30 in action


rdt30 in action

rcv pkt1send ack1

(detect duplicate)

pkt1

sender receiver

rcv pkt1

rcv pkt0

send ack0

send ack1

send ack0

rcv ack0

send pkt0

send pkt1

rcv ack1

send pkt0rcv pkt0

pkt0

pkt0

ack1

ack0

ack0

(c) ACK loss

ack1X

loss

pkt1timeout

resend pkt1

rcv pkt1send ack1

(detect duplicate)

pkt1

sender receiver

rcv pkt1

send ack0rcv ack0

send pkt1

send pkt0rcv pkt0

pkt0

ack0


pkt1timeout

resend pkt1

ack1

send ack1

send pkt0rcv ack1

pkt0

ack1

ack0






packet


U sender =

008 30008

= 000027 L R RTT + L R

=



Dtrans = LR





sender receiver

RTT




U sender =

008 30008

= 000027 L R RTT + L R

=








RTT






U sender =

0024 30008

= 000081 3L R RTT + L R

=










ack for each packet







window




timeout

rdt_send(data)







base=1nextseqnum=1






Wait







GBN in action


(wait)

sender receiver



rcv ack1 send pkt5


Xloss





0 1 2 3 4 5 6 7 8

sender window (N=4)

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8










Selective repeat



timerACK(n) in








receiver




(wait)

sender receiver



rcv ack1 send pkt5


Xloss




record ack3 arrived

0 1 2 3 4 5 6 7 8

sender window (N=4)

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8







0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2

pkt0pkt1pkt2

0 1 2 3 0 1 2 pkt0


0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2XXX


0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2

pkt0pkt1pkt2

0 1 2 3 0 1 2pkt0

0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2


0 1 2 3 0 1 2 pkt3

(a) no problem















control









overwhelm receiver









32 bits

applicationdata

(variable length)


receive window


lennot

used



ACK ACK valid



commands)



Internetchecksum

(as in UDP)








checksum

rwndurg pointer


A

sent ACKed



not usable

window sizeN




checksum

rwndurg pointer





host ACKsreceipt




Host BHost A



Seq=43 ACK=80














100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106time (seconnds)

RTT

(mill

iseco

nds)






T (m

illise

cond

s)



time (seconds)






(typically = 025)













control









congestion control















waitfor

event



start timer



start timer

timeout






lost ACK scenario

Host BHost A


ACK=100


Xtimeo

ut

ACK=100

premature timeout

Host BHost A


ACK=100


timeo

ut

ACK=120


ACK=120

SendBase=100

SendBase=120

SendBase=120

SendBase=92



X

cumulative ACK

Host BHost A


ACK=100


timeo

ut


ACK=120



event at receiver





TCP receiver action














TCP fast retransmit



X


Host BHost A


ACK=100

timeo

ut ACK=100

ACK=100ACK=100

TCP fast retransmit












control



process


TCPcode

IPcode

applicationOS





from sender


flow control


TCP flow control

buffered data


RcvBuffer


















control








application

network




application

network








2-way handshake

Letrsquos talk

OKESTAB

ESTAB


ESTABacc_conn(x)





ESTAB

req_conn(x)


client terminates

serverforgets x



ESTAB

req_conn(x)

data(x+1)

retransmitdata(x+1)

acceptdata(x+1)

choose xreq_conn(x)

ESTAB

ESTAB

acc_conn(x)

client terminates

ESTAB

choose xreq_conn(x)

ESTABacc_conn(x)



forgets x


TCP 3-way handshake

SYNbit=1 Seq=x


ESTAB



ACKbit=1 ACKnum=y+1




SYNSENT

ESTAB

SYN RCVD

client stateLISTEN

server stateLISTEN



closed

listen

SYNrcvd

SYNsent

ESTAB


SYN(seq=x)











FIN_WAIT_2

CLOSE_WAIT

FINbit=1 seq=y

ACKbit=1 ACKnum=y+1


close

can stillsend data


LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2max

segment lifetime

CLOSED



clientSocketclose()











control





a top-10 problem








Host A

original data in

Host B

throughput out

R2

R2

out

in R2de

lay








Host A

in original data

Host B


lsquo








free buffer space

R2

R2

out

in


Host B

A




no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







rsquo increase


Host A out


Host B

Host CHost D


retransmitted data







C2

C2

out

inrsquo










control





loss

cwnd

TCP

send

er

cong

estio

n w

indo

w s

ize


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwndRTT

bytessec






Host A

RTT

Host B

time



















cwnd gt ssthresh

congestionavoidance



new ACK


fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


WRTT bytessec










TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R






















linkphysical


linkphysical

ECN=00 ECN=11

ECE=1

IP datagram

TCP ACK segment






bull UDPbull TCP

next leaving the







sender receiver

state1

state2




eventactions







udt_send(packet)


Wait for call from

below

rdt_rcv(packet)

sender receiver







gtsender









sender









udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

belowsender









udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)








udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)














above


rdt_send(data)




rdt_send(data)


udt_send(sndpkt)



Wait forcall 1 from

above




































above


rdt_send(data)

udt_send(sndpkt)


isACK(rcvpkt1) )


Wait for ACK

0sender FSMfragment





has_seq1(rcvpkt))


fragment













rdt_send(data)

Wait for

ACK0



above


rdt_send(data)






timeout


timeout

rdt_rcv(rcvpkt)

Wait for call 0from

above

Wait for

ACK1

rdt_rcv(rcvpkt)


sender receiver

rcv pkt1

rcv pkt0

send ack0

send ack1

send ack0

rcv ack0

send pkt0

send pkt1

rcv ack1

send pkt0rcv pkt0

pkt0

pkt0

pkt1

ack1

ack0

ack0

(a) no loss

sender receiver

rcv pkt1

rcv pkt0

send ack0

send ack1

send ack0

rcv ack0

send pkt0

send pkt1

rcv ack1

send pkt0rcv pkt0

pkt0

pkt0

ack1

ack0

ack0

(b) packet loss

pkt1X

loss

pkt1timeout

resend pkt1

rdt30 in action


rdt30 in action

rcv pkt1send ack1

(detect duplicate)

pkt1

sender receiver

rcv pkt1

rcv pkt0

send ack0

send ack1

send ack0

rcv ack0

send pkt0

send pkt1

rcv ack1

send pkt0rcv pkt0

pkt0

pkt0

ack1

ack0

ack0

(c) ACK loss

ack1X

loss

pkt1timeout

resend pkt1

rcv pkt1send ack1

(detect duplicate)

pkt1

sender receiver

rcv pkt1

send ack0rcv ack0

send pkt1

send pkt0rcv pkt0

pkt0

ack0


pkt1timeout

resend pkt1

ack1

send ack1

send pkt0rcv ack1

pkt0

ack1

ack0






packet


U sender =

008 30008

= 000027 L R RTT + L R

=



Dtrans = LR





sender receiver

RTT




U sender =

008 30008

= 000027 L R RTT + L R

=








RTT






U sender =

0024 30008

= 000081 3L R RTT + L R

=










ack for each packet







window




timeout

rdt_send(data)







base=1nextseqnum=1






Wait







GBN in action


(wait)

sender receiver



rcv ack1 send pkt5


Xloss





0 1 2 3 4 5 6 7 8

sender window (N=4)

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8










Selective repeat



timerACK(n) in








receiver




(wait)

sender receiver



rcv ack1 send pkt5


Xloss




record ack3 arrived

0 1 2 3 4 5 6 7 8

sender window (N=4)

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8







0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2

pkt0pkt1pkt2

0 1 2 3 0 1 2 pkt0


0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2XXX


0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2

pkt0pkt1pkt2

0 1 2 3 0 1 2pkt0

0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2


0 1 2 3 0 1 2 pkt3

(a) no problem















control









overwhelm receiver









32 bits

applicationdata

(variable length)


receive window


lennot

used



ACK ACK valid



commands)



Internetchecksum

(as in UDP)








checksum

rwndurg pointer


A

sent ACKed



not usable

window sizeN




checksum

rwndurg pointer





host ACKsreceipt




Host BHost A



Seq=43 ACK=80














100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106time (seconnds)

RTT

(mill

iseco

nds)






T (m

illise

cond

s)



time (seconds)






(typically = 025)













control









congestion control















waitfor

event



start timer



start timer

timeout






lost ACK scenario

Host BHost A


ACK=100


Xtimeo

ut

ACK=100

premature timeout

Host BHost A


ACK=100


timeo

ut

ACK=120


ACK=120

SendBase=100

SendBase=120

SendBase=120

SendBase=92



X

cumulative ACK

Host BHost A


ACK=100


timeo

ut


ACK=120



event at receiver





TCP receiver action














TCP fast retransmit



X


Host BHost A


ACK=100

timeo

ut ACK=100

ACK=100ACK=100

TCP fast retransmit












control



process


TCPcode

IPcode

applicationOS





from sender


flow control


TCP flow control

buffered data


RcvBuffer


















control








application

network




application

network








2-way handshake

Letrsquos talk

OKESTAB

ESTAB


ESTABacc_conn(x)





ESTAB

req_conn(x)


client terminates

serverforgets x



ESTAB

req_conn(x)

data(x+1)

retransmitdata(x+1)

acceptdata(x+1)

choose xreq_conn(x)

ESTAB

ESTAB

acc_conn(x)

client terminates

ESTAB

choose xreq_conn(x)

ESTABacc_conn(x)



forgets x


TCP 3-way handshake

SYNbit=1 Seq=x


ESTAB



ACKbit=1 ACKnum=y+1




SYNSENT

ESTAB

SYN RCVD

client stateLISTEN

server stateLISTEN



closed

listen

SYNrcvd

SYNsent

ESTAB


SYN(seq=x)











FIN_WAIT_2

CLOSE_WAIT

FINbit=1 seq=y

ACKbit=1 ACKnum=y+1


close

can stillsend data


LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2max

segment lifetime

CLOSED



clientSocketclose()











control





a top-10 problem








Host A

original data in

Host B

throughput out

R2

R2

out

in R2de

lay








Host A

in original data

Host B


lsquo








free buffer space

R2

R2

out

in


Host B

A




no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







rsquo increase


Host A out


Host B

Host CHost D


retransmitted data







C2

C2

out

inrsquo










control





loss

cwnd

TCP

send

er

cong

estio

n w

indo

w s

ize


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwndRTT

bytessec






Host A

RTT

Host B

time



















cwnd gt ssthresh

congestionavoidance



new ACK


fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


WRTT bytessec










TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R






















linkphysical


linkphysical

ECN=00 ECN=11

ECE=1

IP datagram

TCP ACK segment






bull UDPbull TCP

next leaving the








udt_send(packet)


Wait for call from

below

rdt_rcv(packet)

sender receiver







gtsender









sender









udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

belowsender









udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)








udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)














above


rdt_send(data)




rdt_send(data)


udt_send(sndpkt)



Wait forcall 1 from

above




































above


rdt_send(data)

udt_send(sndpkt)


isACK(rcvpkt1) )


Wait for ACK

0sender FSMfragment





has_seq1(rcvpkt))


fragment













rdt_send(data)

Wait for

ACK0



above


rdt_send(data)






timeout


timeout

rdt_rcv(rcvpkt)

Wait for call 0from

above

Wait for

ACK1

rdt_rcv(rcvpkt)


sender receiver

rcv pkt1

rcv pkt0

send ack0

send ack1

send ack0

rcv ack0

send pkt0

send pkt1

rcv ack1

send pkt0rcv pkt0

pkt0

pkt0

pkt1

ack1

ack0

ack0

(a) no loss

sender receiver

rcv pkt1

rcv pkt0

send ack0

send ack1

send ack0

rcv ack0

send pkt0

send pkt1

rcv ack1

send pkt0rcv pkt0

pkt0

pkt0

ack1

ack0

ack0

(b) packet loss

pkt1X

loss

pkt1timeout

resend pkt1

rdt30 in action


rdt30 in action

rcv pkt1send ack1

(detect duplicate)

pkt1

sender receiver

rcv pkt1

rcv pkt0

send ack0

send ack1

send ack0

rcv ack0

send pkt0

send pkt1

rcv ack1

send pkt0rcv pkt0

pkt0

pkt0

ack1

ack0

ack0

(c) ACK loss

ack1X

loss

pkt1timeout

resend pkt1

rcv pkt1send ack1

(detect duplicate)

pkt1

sender receiver

rcv pkt1

send ack0rcv ack0

send pkt1

send pkt0rcv pkt0

pkt0

ack0


pkt1timeout

resend pkt1

ack1

send ack1

send pkt0rcv ack1

pkt0

ack1

ack0






packet


U sender =

008 30008

= 000027 L R RTT + L R

=



Dtrans = LR





sender receiver

RTT




U sender =

008 30008

= 000027 L R RTT + L R

=








RTT






U sender =

0024 30008

= 000081 3L R RTT + L R

=










ack for each packet







window




timeout

rdt_send(data)







base=1nextseqnum=1






Wait







GBN in action


(wait)

sender receiver



rcv ack1 send pkt5


Xloss





0 1 2 3 4 5 6 7 8

sender window (N=4)

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8










Selective repeat



timerACK(n) in








receiver




(wait)

sender receiver



rcv ack1 send pkt5


Xloss




record ack3 arrived

0 1 2 3 4 5 6 7 8

sender window (N=4)

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8







0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2

pkt0pkt1pkt2

0 1 2 3 0 1 2 pkt0


0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2XXX


0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2

pkt0pkt1pkt2

0 1 2 3 0 1 2pkt0

0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2


0 1 2 3 0 1 2 pkt3

(a) no problem















control









overwhelm receiver









32 bits

applicationdata

(variable length)


receive window


lennot

used



ACK ACK valid



commands)



Internetchecksum

(as in UDP)








checksum

rwndurg pointer


A

sent ACKed



not usable

window sizeN




checksum

rwndurg pointer





host ACKsreceipt




Host BHost A



Seq=43 ACK=80














100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106time (seconnds)

RTT

(mill

iseco

nds)






T (m

illise

cond

s)



time (seconds)






(typically = 025)













control









congestion control















waitfor

event



start timer



start timer

timeout






lost ACK scenario

Host BHost A


ACK=100


Xtimeo

ut

ACK=100

premature timeout

Host BHost A


ACK=100


timeo

ut

ACK=120


ACK=120

SendBase=100

SendBase=120

SendBase=120

SendBase=92



X

cumulative ACK

Host BHost A


ACK=100


timeo

ut


ACK=120



event at receiver





TCP receiver action














TCP fast retransmit



X


Host BHost A


ACK=100

timeo

ut ACK=100

ACK=100ACK=100

TCP fast retransmit












control



process


TCPcode

IPcode

applicationOS





from sender


flow control


TCP flow control

buffered data


RcvBuffer


















control








application

network




application

network








2-way handshake

Letrsquos talk

OKESTAB

ESTAB


ESTABacc_conn(x)





ESTAB

req_conn(x)


client terminates

serverforgets x



ESTAB

req_conn(x)

data(x+1)

retransmitdata(x+1)

acceptdata(x+1)

choose xreq_conn(x)

ESTAB

ESTAB

acc_conn(x)

client terminates

ESTAB

choose xreq_conn(x)

ESTABacc_conn(x)



forgets x


TCP 3-way handshake

SYNbit=1 Seq=x


ESTAB



ACKbit=1 ACKnum=y+1




SYNSENT

ESTAB

SYN RCVD

client stateLISTEN

server stateLISTEN



closed

listen

SYNrcvd

SYNsent

ESTAB


SYN(seq=x)











FIN_WAIT_2

CLOSE_WAIT

FINbit=1 seq=y

ACKbit=1 ACKnum=y+1


close

can stillsend data


LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2max

segment lifetime

CLOSED



clientSocketclose()











control





a top-10 problem








Host A

original data in

Host B

throughput out

R2

R2

out

in R2de

lay








Host A

in original data

Host B


lsquo








free buffer space

R2

R2

out

in


Host B

A




no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







rsquo increase


Host A out


Host B

Host CHost D


retransmitted data







C2

C2

out

inrsquo










control





loss

cwnd

TCP

send

er

cong

estio

n w

indo

w s

ize


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwndRTT

bytessec






Host A

RTT

Host B

time



















cwnd gt ssthresh

congestionavoidance



new ACK


fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


WRTT bytessec










TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R






















linkphysical


linkphysical

ECN=00 ECN=11

ECE=1

IP datagram

TCP ACK segment






bull UDPbull TCP

next leaving the









gtsender









sender









udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

belowsender









udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)








udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)














above


rdt_send(data)




rdt_send(data)


udt_send(sndpkt)



Wait forcall 1 from

above




































above


rdt_send(data)

udt_send(sndpkt)


isACK(rcvpkt1) )


Wait for ACK

0sender FSMfragment





has_seq1(rcvpkt))


fragment













rdt_send(data)

Wait for

ACK0



above


rdt_send(data)






timeout


timeout

rdt_rcv(rcvpkt)

Wait for call 0from

above

Wait for

ACK1

rdt_rcv(rcvpkt)


sender receiver

rcv pkt1

rcv pkt0

send ack0

send ack1

send ack0

rcv ack0

send pkt0

send pkt1

rcv ack1

send pkt0rcv pkt0

pkt0

pkt0

pkt1

ack1

ack0

ack0

(a) no loss

sender receiver

rcv pkt1

rcv pkt0

send ack0

send ack1

send ack0

rcv ack0

send pkt0

send pkt1

rcv ack1

send pkt0rcv pkt0

pkt0

pkt0

ack1

ack0

ack0

(b) packet loss

pkt1X

loss

pkt1timeout

resend pkt1

rdt30 in action


rdt30 in action

rcv pkt1send ack1

(detect duplicate)

pkt1

sender receiver

rcv pkt1

rcv pkt0

send ack0

send ack1

send ack0

rcv ack0

send pkt0

send pkt1

rcv ack1

send pkt0rcv pkt0

pkt0

pkt0

ack1

ack0

ack0

(c) ACK loss

ack1X

loss

pkt1timeout

resend pkt1

rcv pkt1send ack1

(detect duplicate)

pkt1

sender receiver

rcv pkt1

send ack0rcv ack0

send pkt1

send pkt0rcv pkt0

pkt0

ack0


pkt1timeout

resend pkt1

ack1

send ack1

send pkt0rcv ack1

pkt0

ack1

ack0






packet


U sender =

008 30008

= 000027 L R RTT + L R

=



Dtrans = LR





sender receiver

RTT




U sender =

008 30008

= 000027 L R RTT + L R

=








RTT






U sender =

0024 30008

= 000081 3L R RTT + L R

=










ack for each packet







window




timeout

rdt_send(data)







base=1nextseqnum=1






Wait







GBN in action


(wait)

sender receiver



rcv ack1 send pkt5


Xloss





0 1 2 3 4 5 6 7 8

sender window (N=4)

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8










Selective repeat



timerACK(n) in








receiver




(wait)

sender receiver



rcv ack1 send pkt5


Xloss




record ack3 arrived

0 1 2 3 4 5 6 7 8

sender window (N=4)

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8







0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2

pkt0pkt1pkt2

0 1 2 3 0 1 2 pkt0


0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2XXX


0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2

pkt0pkt1pkt2

0 1 2 3 0 1 2pkt0

0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2


0 1 2 3 0 1 2 pkt3

(a) no problem















control









overwhelm receiver









32 bits

applicationdata

(variable length)


receive window


lennot

used



ACK ACK valid



commands)



Internetchecksum

(as in UDP)








checksum

rwndurg pointer


A

sent ACKed



not usable

window sizeN




checksum

rwndurg pointer





host ACKsreceipt




Host BHost A



Seq=43 ACK=80














100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106time (seconnds)

RTT

(mill

iseco

nds)






T (m

illise

cond

s)



time (seconds)






(typically = 025)













control









congestion control















waitfor

event



start timer



start timer

timeout






lost ACK scenario

Host BHost A


ACK=100


Xtimeo

ut

ACK=100

premature timeout

Host BHost A


ACK=100


timeo

ut

ACK=120


ACK=120

SendBase=100

SendBase=120

SendBase=120

SendBase=92



X

cumulative ACK

Host BHost A


ACK=100


timeo

ut


ACK=120



event at receiver





TCP receiver action














TCP fast retransmit



X


Host BHost A


ACK=100

timeo

ut ACK=100

ACK=100ACK=100

TCP fast retransmit












control



process


TCPcode

IPcode

applicationOS





from sender


flow control


TCP flow control

buffered data


RcvBuffer


















control








application

network




application

network








2-way handshake

Letrsquos talk

OKESTAB

ESTAB


ESTABacc_conn(x)





ESTAB

req_conn(x)


client terminates

serverforgets x



ESTAB

req_conn(x)

data(x+1)

retransmitdata(x+1)

acceptdata(x+1)

choose xreq_conn(x)

ESTAB

ESTAB

acc_conn(x)

client terminates

ESTAB

choose xreq_conn(x)

ESTABacc_conn(x)



forgets x


TCP 3-way handshake

SYNbit=1 Seq=x


ESTAB



ACKbit=1 ACKnum=y+1




SYNSENT

ESTAB

SYN RCVD

client stateLISTEN

server stateLISTEN



closed

listen

SYNrcvd

SYNsent

ESTAB


SYN(seq=x)











FIN_WAIT_2

CLOSE_WAIT

FINbit=1 seq=y

ACKbit=1 ACKnum=y+1


close

can stillsend data


LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2max

segment lifetime

CLOSED



clientSocketclose()











control





a top-10 problem








Host A

original data in

Host B

throughput out

R2

R2

out

in R2de

lay








Host A

in original data

Host B


lsquo








free buffer space

R2

R2

out

in


Host B

A




no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







rsquo increase


Host A out


Host B

Host CHost D


retransmitted data







C2

C2

out

inrsquo










control





loss

cwnd

TCP

send

er

cong

estio

n w

indo

w s

ize


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwndRTT

bytessec






Host A

RTT

Host B

time



















cwnd gt ssthresh

congestionavoidance



new ACK


fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


WRTT bytessec










TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R






















linkphysical


linkphysical

ECN=00 ECN=11

ECE=1

IP datagram

TCP ACK segment






bull UDPbull TCP

next leaving the









sender









udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

belowsender









udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)








udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)














above


rdt_send(data)




rdt_send(data)


udt_send(sndpkt)



Wait forcall 1 from

above




































above


rdt_send(data)

udt_send(sndpkt)


isACK(rcvpkt1) )


Wait for ACK

0sender FSMfragment





has_seq1(rcvpkt))


fragment













rdt_send(data)

Wait for

ACK0



above


rdt_send(data)






timeout


timeout

rdt_rcv(rcvpkt)

Wait for call 0from

above

Wait for

ACK1

rdt_rcv(rcvpkt)


sender receiver

rcv pkt1

rcv pkt0

send ack0

send ack1

send ack0

rcv ack0

send pkt0

send pkt1

rcv ack1

send pkt0rcv pkt0

pkt0

pkt0

pkt1

ack1

ack0

ack0

(a) no loss

sender receiver

rcv pkt1

rcv pkt0

send ack0

send ack1

send ack0

rcv ack0

send pkt0

send pkt1

rcv ack1

send pkt0rcv pkt0

pkt0

pkt0

ack1

ack0

ack0

(b) packet loss

pkt1X

loss

pkt1timeout

resend pkt1

rdt30 in action


rdt30 in action

rcv pkt1send ack1

(detect duplicate)

pkt1

sender receiver

rcv pkt1

rcv pkt0

send ack0

send ack1

send ack0

rcv ack0

send pkt0

send pkt1

rcv ack1

send pkt0rcv pkt0

pkt0

pkt0

ack1

ack0

ack0

(c) ACK loss

ack1X

loss

pkt1timeout

resend pkt1

rcv pkt1send ack1

(detect duplicate)

pkt1

sender receiver

rcv pkt1

send ack0rcv ack0

send pkt1

send pkt0rcv pkt0

pkt0

ack0


pkt1timeout

resend pkt1

ack1

send ack1

send pkt0rcv ack1

pkt0

ack1

ack0






packet


U sender =

008 30008

= 000027 L R RTT + L R

=



Dtrans = LR





sender receiver

RTT




U sender =

008 30008

= 000027 L R RTT + L R

=








RTT






U sender =

0024 30008

= 000081 3L R RTT + L R

=










ack for each packet







window




timeout

rdt_send(data)







base=1nextseqnum=1






Wait







GBN in action


(wait)

sender receiver



rcv ack1 send pkt5


Xloss





0 1 2 3 4 5 6 7 8

sender window (N=4)

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8










Selective repeat



timerACK(n) in








receiver




(wait)

sender receiver



rcv ack1 send pkt5


Xloss




record ack3 arrived

0 1 2 3 4 5 6 7 8

sender window (N=4)

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8







0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2

pkt0pkt1pkt2

0 1 2 3 0 1 2 pkt0


0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2XXX


0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2

pkt0pkt1pkt2

0 1 2 3 0 1 2pkt0

0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2


0 1 2 3 0 1 2 pkt3

(a) no problem















control









overwhelm receiver









32 bits

applicationdata

(variable length)


receive window


lennot

used



ACK ACK valid



commands)



Internetchecksum

(as in UDP)








checksum

rwndurg pointer


A

sent ACKed



not usable

window sizeN




checksum

rwndurg pointer





host ACKsreceipt




Host BHost A



Seq=43 ACK=80














100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106time (seconnds)

RTT

(mill

iseco

nds)






T (m

illise

cond

s)



time (seconds)






(typically = 025)













control









congestion control















waitfor

event



start timer



start timer

timeout






lost ACK scenario

Host BHost A


ACK=100


Xtimeo

ut

ACK=100

premature timeout

Host BHost A


ACK=100


timeo

ut

ACK=120


ACK=120

SendBase=100

SendBase=120

SendBase=120

SendBase=92



X

cumulative ACK

Host BHost A


ACK=100


timeo

ut


ACK=120



event at receiver





TCP receiver action














TCP fast retransmit



X


Host BHost A


ACK=100

timeo

ut ACK=100

ACK=100ACK=100

TCP fast retransmit












control



process


TCPcode

IPcode

applicationOS





from sender


flow control


TCP flow control

buffered data


RcvBuffer


















control








application

network




application

network








2-way handshake

Letrsquos talk

OKESTAB

ESTAB


ESTABacc_conn(x)





ESTAB

req_conn(x)


client terminates

serverforgets x



ESTAB

req_conn(x)

data(x+1)

retransmitdata(x+1)

acceptdata(x+1)

choose xreq_conn(x)

ESTAB

ESTAB

acc_conn(x)

client terminates

ESTAB

choose xreq_conn(x)

ESTABacc_conn(x)



forgets x


TCP 3-way handshake

SYNbit=1 Seq=x


ESTAB



ACKbit=1 ACKnum=y+1




SYNSENT

ESTAB

SYN RCVD

client stateLISTEN

server stateLISTEN



closed

listen

SYNrcvd

SYNsent

ESTAB


SYN(seq=x)











FIN_WAIT_2

CLOSE_WAIT

FINbit=1 seq=y

ACKbit=1 ACKnum=y+1


close

can stillsend data


LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2max

segment lifetime

CLOSED



clientSocketclose()











control





a top-10 problem








Host A

original data in

Host B

throughput out

R2

R2

out

in R2de

lay








Host A

in original data

Host B


lsquo








free buffer space

R2

R2

out

in


Host B

A




no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







rsquo increase


Host A out


Host B

Host CHost D


retransmitted data







C2

C2

out

inrsquo










control





loss

cwnd

TCP

send

er

cong

estio

n w

indo

w s

ize


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwndRTT

bytessec






Host A

RTT

Host B

time



















cwnd gt ssthresh

congestionavoidance



new ACK


fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


WRTT bytessec










TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R






















linkphysical


linkphysical

ECN=00 ECN=11

ECE=1

IP datagram

TCP ACK segment






bull UDPbull TCP

next leaving the










udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

belowsender









udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)








udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)














above


rdt_send(data)




rdt_send(data)


udt_send(sndpkt)



Wait forcall 1 from

above




































above


rdt_send(data)

udt_send(sndpkt)


isACK(rcvpkt1) )


Wait for ACK

0sender FSMfragment





has_seq1(rcvpkt))


fragment













rdt_send(data)

Wait for

ACK0



above


rdt_send(data)






timeout


timeout

rdt_rcv(rcvpkt)

Wait for call 0from

above

Wait for

ACK1

rdt_rcv(rcvpkt)


sender receiver

rcv pkt1

rcv pkt0

send ack0

send ack1

send ack0

rcv ack0

send pkt0

send pkt1

rcv ack1

send pkt0rcv pkt0

pkt0

pkt0

pkt1

ack1

ack0

ack0

(a) no loss

sender receiver

rcv pkt1

rcv pkt0

send ack0

send ack1

send ack0

rcv ack0

send pkt0

send pkt1

rcv ack1

send pkt0rcv pkt0

pkt0

pkt0

ack1

ack0

ack0

(b) packet loss

pkt1X

loss

pkt1timeout

resend pkt1

rdt30 in action


rdt30 in action

rcv pkt1send ack1

(detect duplicate)

pkt1

sender receiver

rcv pkt1

rcv pkt0

send ack0

send ack1

send ack0

rcv ack0

send pkt0

send pkt1

rcv ack1

send pkt0rcv pkt0

pkt0

pkt0

ack1

ack0

ack0

(c) ACK loss

ack1X

loss

pkt1timeout

resend pkt1

rcv pkt1send ack1

(detect duplicate)

pkt1

sender receiver

rcv pkt1

send ack0rcv ack0

send pkt1

send pkt0rcv pkt0

pkt0

ack0


pkt1timeout

resend pkt1

ack1

send ack1

send pkt0rcv ack1

pkt0

ack1

ack0






packet


U sender =

008 30008

= 000027 L R RTT + L R

=



Dtrans = LR





sender receiver

RTT




U sender =

008 30008

= 000027 L R RTT + L R

=








RTT






U sender =

0024 30008

= 000081 3L R RTT + L R

=










ack for each packet







window




timeout

rdt_send(data)







base=1nextseqnum=1






Wait







GBN in action


(wait)

sender receiver



rcv ack1 send pkt5


Xloss





0 1 2 3 4 5 6 7 8

sender window (N=4)

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8










Selective repeat



timerACK(n) in








receiver




(wait)

sender receiver



rcv ack1 send pkt5


Xloss




record ack3 arrived

0 1 2 3 4 5 6 7 8

sender window (N=4)

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8







0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2

pkt0pkt1pkt2

0 1 2 3 0 1 2 pkt0


0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2XXX


0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2

pkt0pkt1pkt2

0 1 2 3 0 1 2pkt0

0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2


0 1 2 3 0 1 2 pkt3

(a) no problem















control









overwhelm receiver









32 bits

applicationdata

(variable length)


receive window


lennot

used



ACK ACK valid



commands)



Internetchecksum

(as in UDP)








checksum

rwndurg pointer


A

sent ACKed



not usable

window sizeN




checksum

rwndurg pointer





host ACKsreceipt




Host BHost A



Seq=43 ACK=80














100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106time (seconnds)

RTT

(mill

iseco

nds)






T (m

illise

cond

s)



time (seconds)






(typically = 025)













control









congestion control















waitfor

event



start timer



start timer

timeout






lost ACK scenario

Host BHost A


ACK=100


Xtimeo

ut

ACK=100

premature timeout

Host BHost A


ACK=100


timeo

ut

ACK=120


ACK=120

SendBase=100

SendBase=120

SendBase=120

SendBase=92



X

cumulative ACK

Host BHost A


ACK=100


timeo

ut


ACK=120



event at receiver





TCP receiver action














TCP fast retransmit



X


Host BHost A


ACK=100

timeo

ut ACK=100

ACK=100ACK=100

TCP fast retransmit












control



process


TCPcode

IPcode

applicationOS





from sender


flow control


TCP flow control

buffered data


RcvBuffer


















control








application

network




application

network








2-way handshake

Letrsquos talk

OKESTAB

ESTAB


ESTABacc_conn(x)





ESTAB

req_conn(x)


client terminates

serverforgets x



ESTAB

req_conn(x)

data(x+1)

retransmitdata(x+1)

acceptdata(x+1)

choose xreq_conn(x)

ESTAB

ESTAB

acc_conn(x)

client terminates

ESTAB

choose xreq_conn(x)

ESTABacc_conn(x)



forgets x


TCP 3-way handshake

SYNbit=1 Seq=x


ESTAB



ACKbit=1 ACKnum=y+1




SYNSENT

ESTAB

SYN RCVD

client stateLISTEN

server stateLISTEN



closed

listen

SYNrcvd

SYNsent

ESTAB


SYN(seq=x)











FIN_WAIT_2

CLOSE_WAIT

FINbit=1 seq=y

ACKbit=1 ACKnum=y+1


close

can stillsend data


LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2max

segment lifetime

CLOSED



clientSocketclose()











control





a top-10 problem








Host A

original data in

Host B

throughput out

R2

R2

out

in R2de

lay








Host A

in original data

Host B


lsquo








free buffer space

R2

R2

out

in


Host B

A




no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







rsquo increase


Host A out


Host B

Host CHost D


retransmitted data







C2

C2

out

inrsquo










control





loss

cwnd

TCP

send

er

cong

estio

n w

indo

w s

ize


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwndRTT

bytessec






Host A

RTT

Host B

time



















cwnd gt ssthresh

congestionavoidance



new ACK


fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


WRTT bytessec










TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R






















linkphysical


linkphysical

ECN=00 ECN=11

ECE=1

IP datagram

TCP ACK segment






bull UDPbull TCP

next leaving the










udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)








udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)














above


rdt_send(data)




rdt_send(data)


udt_send(sndpkt)



Wait forcall 1 from

above




































above


rdt_send(data)

udt_send(sndpkt)


isACK(rcvpkt1) )


Wait for ACK

0sender FSMfragment





has_seq1(rcvpkt))


fragment













rdt_send(data)

Wait for

ACK0



above


rdt_send(data)






timeout


timeout

rdt_rcv(rcvpkt)

Wait for call 0from

above

Wait for

ACK1

rdt_rcv(rcvpkt)


sender receiver

rcv pkt1

rcv pkt0

send ack0

send ack1

send ack0

rcv ack0

send pkt0

send pkt1

rcv ack1

send pkt0rcv pkt0

pkt0

pkt0

pkt1

ack1

ack0

ack0

(a) no loss

sender receiver

rcv pkt1

rcv pkt0

send ack0

send ack1

send ack0

rcv ack0

send pkt0

send pkt1

rcv ack1

send pkt0rcv pkt0

pkt0

pkt0

ack1

ack0

ack0

(b) packet loss

pkt1X

loss

pkt1timeout

resend pkt1

rdt30 in action


rdt30 in action

rcv pkt1send ack1

(detect duplicate)

pkt1

sender receiver

rcv pkt1

rcv pkt0

send ack0

send ack1

send ack0

rcv ack0

send pkt0

send pkt1

rcv ack1

send pkt0rcv pkt0

pkt0

pkt0

ack1

ack0

ack0

(c) ACK loss

ack1X

loss

pkt1timeout

resend pkt1

rcv pkt1send ack1

(detect duplicate)

pkt1

sender receiver

rcv pkt1

send ack0rcv ack0

send pkt1

send pkt0rcv pkt0

pkt0

ack0


pkt1timeout

resend pkt1

ack1

send ack1

send pkt0rcv ack1

pkt0

ack1

ack0






packet


U sender =

008 30008

= 000027 L R RTT + L R

=



Dtrans = LR





sender receiver

RTT




U sender =

008 30008

= 000027 L R RTT + L R

=








RTT






U sender =

0024 30008

= 000081 3L R RTT + L R

=










ack for each packet







window




timeout

rdt_send(data)







base=1nextseqnum=1






Wait







GBN in action


(wait)

sender receiver



rcv ack1 send pkt5


Xloss





0 1 2 3 4 5 6 7 8

sender window (N=4)

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8










Selective repeat



timerACK(n) in








receiver




(wait)

sender receiver



rcv ack1 send pkt5


Xloss




record ack3 arrived

0 1 2 3 4 5 6 7 8

sender window (N=4)

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8







0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2

pkt0pkt1pkt2

0 1 2 3 0 1 2 pkt0


0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2XXX


0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2

pkt0pkt1pkt2

0 1 2 3 0 1 2pkt0

0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2


0 1 2 3 0 1 2 pkt3

(a) no problem















control









overwhelm receiver









32 bits

applicationdata

(variable length)


receive window


lennot

used



ACK ACK valid



commands)



Internetchecksum

(as in UDP)








checksum

rwndurg pointer


A

sent ACKed



not usable

window sizeN




checksum

rwndurg pointer





host ACKsreceipt




Host BHost A



Seq=43 ACK=80














100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106time (seconnds)

RTT

(mill

iseco

nds)






T (m

illise

cond

s)



time (seconds)






(typically = 025)













control









congestion control















waitfor

event



start timer



start timer

timeout






lost ACK scenario

Host BHost A


ACK=100


Xtimeo

ut

ACK=100

premature timeout

Host BHost A


ACK=100


timeo

ut

ACK=120


ACK=120

SendBase=100

SendBase=120

SendBase=120

SendBase=92



X

cumulative ACK

Host BHost A


ACK=100


timeo

ut


ACK=120



event at receiver





TCP receiver action














TCP fast retransmit



X


Host BHost A


ACK=100

timeo

ut ACK=100

ACK=100ACK=100

TCP fast retransmit












control



process


TCPcode

IPcode

applicationOS





from sender


flow control


TCP flow control

buffered data


RcvBuffer


















control








application

network




application

network








2-way handshake

Letrsquos talk

OKESTAB

ESTAB


ESTABacc_conn(x)





ESTAB

req_conn(x)


client terminates

serverforgets x



ESTAB

req_conn(x)

data(x+1)

retransmitdata(x+1)

acceptdata(x+1)

choose xreq_conn(x)

ESTAB

ESTAB

acc_conn(x)

client terminates

ESTAB

choose xreq_conn(x)

ESTABacc_conn(x)



forgets x


TCP 3-way handshake

SYNbit=1 Seq=x


ESTAB



ACKbit=1 ACKnum=y+1




SYNSENT

ESTAB

SYN RCVD

client stateLISTEN

server stateLISTEN



closed

listen

SYNrcvd

SYNsent

ESTAB


SYN(seq=x)











FIN_WAIT_2

CLOSE_WAIT

FINbit=1 seq=y

ACKbit=1 ACKnum=y+1


close

can stillsend data


LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2max

segment lifetime

CLOSED



clientSocketclose()











control





a top-10 problem








Host A

original data in

Host B

throughput out

R2

R2

out

in R2de

lay








Host A

in original data

Host B


lsquo








free buffer space

R2

R2

out

in


Host B

A




no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







rsquo increase


Host A out


Host B

Host CHost D


retransmitted data







C2

C2

out

inrsquo










control





loss

cwnd

TCP

send

er

cong

estio

n w

indo

w s

ize


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwndRTT

bytessec






Host A

RTT

Host B

time



















cwnd gt ssthresh

congestionavoidance



new ACK


fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


WRTT bytessec










TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R






















linkphysical


linkphysical

ECN=00 ECN=11

ECE=1

IP datagram

TCP ACK segment






bull UDPbull TCP

next leaving the










udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)














above


rdt_send(data)




rdt_send(data)


udt_send(sndpkt)



Wait forcall 1 from

above




































above


rdt_send(data)

udt_send(sndpkt)


isACK(rcvpkt1) )


Wait for ACK

0sender FSMfragment





has_seq1(rcvpkt))


fragment













rdt_send(data)

Wait for

ACK0



above


rdt_send(data)






timeout


timeout

rdt_rcv(rcvpkt)

Wait for call 0from

above

Wait for

ACK1

rdt_rcv(rcvpkt)


sender receiver

rcv pkt1

rcv pkt0

send ack0

send ack1

send ack0

rcv ack0

send pkt0

send pkt1

rcv ack1

send pkt0rcv pkt0

pkt0

pkt0

pkt1

ack1

ack0

ack0

(a) no loss

sender receiver

rcv pkt1

rcv pkt0

send ack0

send ack1

send ack0

rcv ack0

send pkt0

send pkt1

rcv ack1

send pkt0rcv pkt0

pkt0

pkt0

ack1

ack0

ack0

(b) packet loss

pkt1X

loss

pkt1timeout

resend pkt1

rdt30 in action


rdt30 in action

rcv pkt1send ack1

(detect duplicate)

pkt1

sender receiver

rcv pkt1

rcv pkt0

send ack0

send ack1

send ack0

rcv ack0

send pkt0

send pkt1

rcv ack1

send pkt0rcv pkt0

pkt0

pkt0

ack1

ack0

ack0

(c) ACK loss

ack1X

loss

pkt1timeout

resend pkt1

rcv pkt1send ack1

(detect duplicate)

pkt1

sender receiver

rcv pkt1

send ack0rcv ack0

send pkt1

send pkt0rcv pkt0

pkt0

ack0


pkt1timeout

resend pkt1

ack1

send ack1

send pkt0rcv ack1

pkt0

ack1

ack0






packet


U sender =

008 30008

= 000027 L R RTT + L R

=



Dtrans = LR





sender receiver

RTT




U sender =

008 30008

= 000027 L R RTT + L R

=








RTT






U sender =

0024 30008

= 000081 3L R RTT + L R

=










ack for each packet







window




timeout

rdt_send(data)







base=1nextseqnum=1






Wait







GBN in action


(wait)

sender receiver



rcv ack1 send pkt5


Xloss





0 1 2 3 4 5 6 7 8

sender window (N=4)

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8










Selective repeat



timerACK(n) in








receiver




(wait)

sender receiver



rcv ack1 send pkt5


Xloss




record ack3 arrived

0 1 2 3 4 5 6 7 8

sender window (N=4)

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8







0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2

pkt0pkt1pkt2

0 1 2 3 0 1 2 pkt0


0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2XXX


0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2

pkt0pkt1pkt2

0 1 2 3 0 1 2pkt0

0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2


0 1 2 3 0 1 2 pkt3

(a) no problem















control









overwhelm receiver









32 bits

applicationdata

(variable length)


receive window


lennot

used



ACK ACK valid



commands)



Internetchecksum

(as in UDP)








checksum

rwndurg pointer


A

sent ACKed



not usable

window sizeN




checksum

rwndurg pointer





host ACKsreceipt




Host BHost A



Seq=43 ACK=80














100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106time (seconnds)

RTT

(mill

iseco

nds)






T (m

illise

cond

s)



time (seconds)






(typically = 025)













control









congestion control















waitfor

event



start timer



start timer

timeout






lost ACK scenario

Host BHost A


ACK=100


Xtimeo

ut

ACK=100

premature timeout

Host BHost A


ACK=100


timeo

ut

ACK=120


ACK=120

SendBase=100

SendBase=120

SendBase=120

SendBase=92



X

cumulative ACK

Host BHost A


ACK=100


timeo

ut


ACK=120



event at receiver





TCP receiver action














TCP fast retransmit



X


Host BHost A


ACK=100

timeo

ut ACK=100

ACK=100ACK=100

TCP fast retransmit












control



process


TCPcode

IPcode

applicationOS





from sender


flow control


TCP flow control

buffered data


RcvBuffer


















control








application

network




application

network








2-way handshake

Letrsquos talk

OKESTAB

ESTAB


ESTABacc_conn(x)





ESTAB

req_conn(x)


client terminates

serverforgets x



ESTAB

req_conn(x)

data(x+1)

retransmitdata(x+1)

acceptdata(x+1)

choose xreq_conn(x)

ESTAB

ESTAB

acc_conn(x)

client terminates

ESTAB

choose xreq_conn(x)

ESTABacc_conn(x)



forgets x


TCP 3-way handshake

SYNbit=1 Seq=x


ESTAB



ACKbit=1 ACKnum=y+1




SYNSENT

ESTAB

SYN RCVD

client stateLISTEN

server stateLISTEN



closed

listen

SYNrcvd

SYNsent

ESTAB


SYN(seq=x)











FIN_WAIT_2

CLOSE_WAIT

FINbit=1 seq=y

ACKbit=1 ACKnum=y+1


close

can stillsend data


LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2max

segment lifetime

CLOSED



clientSocketclose()











control





a top-10 problem








Host A

original data in

Host B

throughput out

R2

R2

out

in R2de

lay








Host A

in original data

Host B


lsquo








free buffer space

R2

R2

out

in


Host B

A




no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







rsquo increase


Host A out


Host B

Host CHost D


retransmitted data







C2

C2

out

inrsquo










control





loss

cwnd

TCP

send

er

cong

estio

n w

indo

w s

ize


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwndRTT

bytessec






Host A

RTT

Host B

time



















cwnd gt ssthresh

congestionavoidance



new ACK


fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


WRTT bytessec










TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R






















linkphysical


linkphysical

ECN=00 ECN=11

ECE=1

IP datagram

TCP ACK segment






bull UDPbull TCP

next leaving the
















above


rdt_send(data)




rdt_send(data)


udt_send(sndpkt)



Wait forcall 1 from

above




































above


rdt_send(data)

udt_send(sndpkt)


isACK(rcvpkt1) )


Wait for ACK

0sender FSMfragment





has_seq1(rcvpkt))


fragment













rdt_send(data)

Wait for

ACK0



above


rdt_send(data)






timeout


timeout

rdt_rcv(rcvpkt)

Wait for call 0from

above

Wait for

ACK1

rdt_rcv(rcvpkt)


sender receiver

rcv pkt1

rcv pkt0

send ack0

send ack1

send ack0

rcv ack0

send pkt0

send pkt1

rcv ack1

send pkt0rcv pkt0

pkt0

pkt0

pkt1

ack1

ack0

ack0

(a) no loss

sender receiver

rcv pkt1

rcv pkt0

send ack0

send ack1

send ack0

rcv ack0

send pkt0

send pkt1

rcv ack1

send pkt0rcv pkt0

pkt0

pkt0

ack1

ack0

ack0

(b) packet loss

pkt1X

loss

pkt1timeout

resend pkt1

rdt30 in action


rdt30 in action

rcv pkt1send ack1

(detect duplicate)

pkt1

sender receiver

rcv pkt1

rcv pkt0

send ack0

send ack1

send ack0

rcv ack0

send pkt0

send pkt1

rcv ack1

send pkt0rcv pkt0

pkt0

pkt0

ack1

ack0

ack0

(c) ACK loss

ack1X

loss

pkt1timeout

resend pkt1

rcv pkt1send ack1

(detect duplicate)

pkt1

sender receiver

rcv pkt1

send ack0rcv ack0

send pkt1

send pkt0rcv pkt0

pkt0

ack0


pkt1timeout

resend pkt1

ack1

send ack1

send pkt0rcv ack1

pkt0

ack1

ack0






packet


U sender =

008 30008

= 000027 L R RTT + L R

=



Dtrans = LR





sender receiver

RTT




U sender =

008 30008

= 000027 L R RTT + L R

=








RTT






U sender =

0024 30008

= 000081 3L R RTT + L R

=










ack for each packet







window




timeout

rdt_send(data)







base=1nextseqnum=1






Wait







GBN in action


(wait)

sender receiver



rcv ack1 send pkt5


Xloss





0 1 2 3 4 5 6 7 8

sender window (N=4)

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8










Selective repeat



timerACK(n) in








receiver




(wait)

sender receiver



rcv ack1 send pkt5


Xloss




record ack3 arrived

0 1 2 3 4 5 6 7 8

sender window (N=4)

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8







0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2

pkt0pkt1pkt2

0 1 2 3 0 1 2 pkt0


0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2XXX


0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2

pkt0pkt1pkt2

0 1 2 3 0 1 2pkt0

0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2


0 1 2 3 0 1 2 pkt3

(a) no problem















control









overwhelm receiver









32 bits

applicationdata

(variable length)


receive window


lennot

used



ACK ACK valid



commands)



Internetchecksum

(as in UDP)








checksum

rwndurg pointer


A

sent ACKed



not usable

window sizeN




checksum

rwndurg pointer





host ACKsreceipt




Host BHost A



Seq=43 ACK=80














100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106time (seconnds)

RTT

(mill

iseco

nds)






T (m

illise

cond

s)



time (seconds)






(typically = 025)













control









congestion control















waitfor

event



start timer



start timer

timeout






lost ACK scenario

Host BHost A


ACK=100


Xtimeo

ut

ACK=100

premature timeout

Host BHost A


ACK=100


timeo

ut

ACK=120


ACK=120

SendBase=100

SendBase=120

SendBase=120

SendBase=92



X

cumulative ACK

Host BHost A


ACK=100


timeo

ut


ACK=120



event at receiver





TCP receiver action














TCP fast retransmit



X


Host BHost A


ACK=100

timeo

ut ACK=100

ACK=100ACK=100

TCP fast retransmit












control



process


TCPcode

IPcode

applicationOS





from sender


flow control


TCP flow control

buffered data


RcvBuffer


















control








application

network




application

network








2-way handshake

Letrsquos talk

OKESTAB

ESTAB


ESTABacc_conn(x)





ESTAB

req_conn(x)


client terminates

serverforgets x



ESTAB

req_conn(x)

data(x+1)

retransmitdata(x+1)

acceptdata(x+1)

choose xreq_conn(x)

ESTAB

ESTAB

acc_conn(x)

client terminates

ESTAB

choose xreq_conn(x)

ESTABacc_conn(x)



forgets x


TCP 3-way handshake

SYNbit=1 Seq=x


ESTAB



ACKbit=1 ACKnum=y+1




SYNSENT

ESTAB

SYN RCVD

client stateLISTEN

server stateLISTEN



closed

listen

SYNrcvd

SYNsent

ESTAB


SYN(seq=x)











FIN_WAIT_2

CLOSE_WAIT

FINbit=1 seq=y

ACKbit=1 ACKnum=y+1


close

can stillsend data


LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2max

segment lifetime

CLOSED



clientSocketclose()











control





a top-10 problem








Host A

original data in

Host B

throughput out

R2

R2

out

in R2de

lay








Host A

in original data

Host B


lsquo








free buffer space

R2

R2

out

in


Host B

A




no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







rsquo increase


Host A out


Host B

Host CHost D


retransmitted data







C2

C2

out

inrsquo










control





loss

cwnd

TCP

send

er

cong

estio

n w

indo

w s

ize


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwndRTT

bytessec






Host A

RTT

Host B

time



















cwnd gt ssthresh

congestionavoidance



new ACK


fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


WRTT bytessec










TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R






















linkphysical


linkphysical

ECN=00 ECN=11

ECE=1

IP datagram

TCP ACK segment






bull UDPbull TCP

next leaving the





































above


rdt_send(data)

udt_send(sndpkt)


isACK(rcvpkt1) )


Wait for ACK

0sender FSMfragment





has_seq1(rcvpkt))


fragment













rdt_send(data)

Wait for

ACK0



above


rdt_send(data)






timeout


timeout

rdt_rcv(rcvpkt)

Wait for call 0from

above

Wait for

ACK1

rdt_rcv(rcvpkt)


sender receiver

rcv pkt1

rcv pkt0

send ack0

send ack1

send ack0

rcv ack0

send pkt0

send pkt1

rcv ack1

send pkt0rcv pkt0

pkt0

pkt0

pkt1

ack1

ack0

ack0

(a) no loss

sender receiver

rcv pkt1

rcv pkt0

send ack0

send ack1

send ack0

rcv ack0

send pkt0

send pkt1

rcv ack1

send pkt0rcv pkt0

pkt0

pkt0

ack1

ack0

ack0

(b) packet loss

pkt1X

loss

pkt1timeout

resend pkt1

rdt30 in action


rdt30 in action

rcv pkt1send ack1

(detect duplicate)

pkt1

sender receiver

rcv pkt1

rcv pkt0

send ack0

send ack1

send ack0

rcv ack0

send pkt0

send pkt1

rcv ack1

send pkt0rcv pkt0

pkt0

pkt0

ack1

ack0

ack0

(c) ACK loss

ack1X

loss

pkt1timeout

resend pkt1

rcv pkt1send ack1

(detect duplicate)

pkt1

sender receiver

rcv pkt1

send ack0rcv ack0

send pkt1

send pkt0rcv pkt0

pkt0

ack0


pkt1timeout

resend pkt1

ack1

send ack1

send pkt0rcv ack1

pkt0

ack1

ack0






packet


U sender =

008 30008

= 000027 L R RTT + L R

=



Dtrans = LR





sender receiver

RTT




U sender =

008 30008

= 000027 L R RTT + L R

=








RTT






U sender =

0024 30008

= 000081 3L R RTT + L R

=










ack for each packet







window




timeout

rdt_send(data)







base=1nextseqnum=1






Wait







GBN in action


(wait)

sender receiver



rcv ack1 send pkt5


Xloss





0 1 2 3 4 5 6 7 8

sender window (N=4)

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8










Selective repeat



timerACK(n) in








receiver




(wait)

sender receiver



rcv ack1 send pkt5


Xloss




record ack3 arrived

0 1 2 3 4 5 6 7 8

sender window (N=4)

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8







0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2

pkt0pkt1pkt2

0 1 2 3 0 1 2 pkt0


0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2XXX


0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2

pkt0pkt1pkt2

0 1 2 3 0 1 2pkt0

0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2


0 1 2 3 0 1 2 pkt3

(a) no problem















control









overwhelm receiver









32 bits

applicationdata

(variable length)


receive window


lennot

used



ACK ACK valid



commands)



Internetchecksum

(as in UDP)








checksum

rwndurg pointer


A

sent ACKed



not usable

window sizeN




checksum

rwndurg pointer





host ACKsreceipt




Host BHost A



Seq=43 ACK=80














100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106time (seconnds)

RTT

(mill

iseco

nds)






T (m

illise

cond

s)



time (seconds)






(typically = 025)













control









congestion control















waitfor

event



start timer



start timer

timeout






lost ACK scenario

Host BHost A


ACK=100


Xtimeo

ut

ACK=100

premature timeout

Host BHost A


ACK=100


timeo

ut

ACK=120


ACK=120

SendBase=100

SendBase=120

SendBase=120

SendBase=92



X

cumulative ACK

Host BHost A


ACK=100


timeo

ut


ACK=120



event at receiver





TCP receiver action














TCP fast retransmit



X


Host BHost A


ACK=100

timeo

ut ACK=100

ACK=100ACK=100

TCP fast retransmit












control



process


TCPcode

IPcode

applicationOS





from sender


flow control


TCP flow control

buffered data


RcvBuffer


















control








application

network




application

network








2-way handshake

Letrsquos talk

OKESTAB

ESTAB


ESTABacc_conn(x)





ESTAB

req_conn(x)


client terminates

serverforgets x



ESTAB

req_conn(x)

data(x+1)

retransmitdata(x+1)

acceptdata(x+1)

choose xreq_conn(x)

ESTAB

ESTAB

acc_conn(x)

client terminates

ESTAB

choose xreq_conn(x)

ESTABacc_conn(x)



forgets x


TCP 3-way handshake

SYNbit=1 Seq=x


ESTAB



ACKbit=1 ACKnum=y+1




SYNSENT

ESTAB

SYN RCVD

client stateLISTEN

server stateLISTEN



closed

listen

SYNrcvd

SYNsent

ESTAB


SYN(seq=x)











FIN_WAIT_2

CLOSE_WAIT

FINbit=1 seq=y

ACKbit=1 ACKnum=y+1


close

can stillsend data


LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2max

segment lifetime

CLOSED



clientSocketclose()











control





a top-10 problem








Host A

original data in

Host B

throughput out

R2

R2

out

in R2de

lay








Host A

in original data

Host B


lsquo








free buffer space

R2

R2

out

in


Host B

A




no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







rsquo increase


Host A out


Host B

Host CHost D


retransmitted data







C2

C2

out

inrsquo










control





loss

cwnd

TCP

send

er

cong

estio

n w

indo

w s

ize


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwndRTT

bytessec






Host A

RTT

Host B

time



















cwnd gt ssthresh

congestionavoidance



new ACK


fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


WRTT bytessec










TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R






















linkphysical


linkphysical

ECN=00 ECN=11

ECE=1

IP datagram

TCP ACK segment






bull UDPbull TCP

next leaving the















rdt_send(data)

Wait for

ACK0



above


rdt_send(data)






timeout


timeout

rdt_rcv(rcvpkt)

Wait for call 0from

above

Wait for

ACK1

rdt_rcv(rcvpkt)


sender receiver

rcv pkt1

rcv pkt0

send ack0

send ack1

send ack0

rcv ack0

send pkt0

send pkt1

rcv ack1

send pkt0rcv pkt0

pkt0

pkt0

pkt1

ack1

ack0

ack0

(a) no loss

sender receiver

rcv pkt1

rcv pkt0

send ack0

send ack1

send ack0

rcv ack0

send pkt0

send pkt1

rcv ack1

send pkt0rcv pkt0

pkt0

pkt0

ack1

ack0

ack0

(b) packet loss

pkt1X

loss

pkt1timeout

resend pkt1

rdt30 in action


rdt30 in action

rcv pkt1send ack1

(detect duplicate)

pkt1

sender receiver

rcv pkt1

rcv pkt0

send ack0

send ack1

send ack0

rcv ack0

send pkt0

send pkt1

rcv ack1

send pkt0rcv pkt0

pkt0

pkt0

ack1

ack0

ack0

(c) ACK loss

ack1X

loss

pkt1timeout

resend pkt1

rcv pkt1send ack1

(detect duplicate)

pkt1

sender receiver

rcv pkt1

send ack0rcv ack0

send pkt1

send pkt0rcv pkt0

pkt0

ack0


pkt1timeout

resend pkt1

ack1

send ack1

send pkt0rcv ack1

pkt0

ack1

ack0






packet


U sender =

008 30008

= 000027 L R RTT + L R

=



Dtrans = LR





sender receiver

RTT




U sender =

008 30008

= 000027 L R RTT + L R

=








RTT






U sender =

0024 30008

= 000081 3L R RTT + L R

=










ack for each packet







window




timeout

rdt_send(data)







base=1nextseqnum=1






Wait







GBN in action


(wait)

sender receiver



rcv ack1 send pkt5


Xloss





0 1 2 3 4 5 6 7 8

sender window (N=4)

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8










Selective repeat



timerACK(n) in








receiver




(wait)

sender receiver



rcv ack1 send pkt5


Xloss




record ack3 arrived

0 1 2 3 4 5 6 7 8

sender window (N=4)

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8







0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2

pkt0pkt1pkt2

0 1 2 3 0 1 2 pkt0


0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2XXX


0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2

pkt0pkt1pkt2

0 1 2 3 0 1 2pkt0

0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2


0 1 2 3 0 1 2 pkt3

(a) no problem















control









overwhelm receiver









32 bits

applicationdata

(variable length)


receive window


lennot

used



ACK ACK valid



commands)



Internetchecksum

(as in UDP)








checksum

rwndurg pointer


A

sent ACKed



not usable

window sizeN




checksum

rwndurg pointer





host ACKsreceipt




Host BHost A



Seq=43 ACK=80














100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106time (seconnds)

RTT

(mill

iseco

nds)






T (m

illise

cond

s)



time (seconds)






(typically = 025)













control









congestion control















waitfor

event



start timer



start timer

timeout






lost ACK scenario

Host BHost A


ACK=100


Xtimeo

ut

ACK=100

premature timeout

Host BHost A


ACK=100


timeo

ut

ACK=120


ACK=120

SendBase=100

SendBase=120

SendBase=120

SendBase=92



X

cumulative ACK

Host BHost A


ACK=100


timeo

ut


ACK=120



event at receiver





TCP receiver action














TCP fast retransmit



X


Host BHost A


ACK=100

timeo

ut ACK=100

ACK=100ACK=100

TCP fast retransmit












control



process


TCPcode

IPcode

applicationOS





from sender


flow control


TCP flow control

buffered data


RcvBuffer


















control








application

network




application

network








2-way handshake

Letrsquos talk

OKESTAB

ESTAB


ESTABacc_conn(x)





ESTAB

req_conn(x)


client terminates

serverforgets x



ESTAB

req_conn(x)

data(x+1)

retransmitdata(x+1)

acceptdata(x+1)

choose xreq_conn(x)

ESTAB

ESTAB

acc_conn(x)

client terminates

ESTAB

choose xreq_conn(x)

ESTABacc_conn(x)



forgets x


TCP 3-way handshake

SYNbit=1 Seq=x


ESTAB



ACKbit=1 ACKnum=y+1




SYNSENT

ESTAB

SYN RCVD

client stateLISTEN

server stateLISTEN



closed

listen

SYNrcvd

SYNsent

ESTAB


SYN(seq=x)











FIN_WAIT_2

CLOSE_WAIT

FINbit=1 seq=y

ACKbit=1 ACKnum=y+1


close

can stillsend data


LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2max

segment lifetime

CLOSED



clientSocketclose()











control





a top-10 problem








Host A

original data in

Host B

throughput out

R2

R2

out

in R2de

lay








Host A

in original data

Host B


lsquo








free buffer space

R2

R2

out

in


Host B

A




no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







rsquo increase


Host A out


Host B

Host CHost D


retransmitted data







C2

C2

out

inrsquo










control





loss

cwnd

TCP

send

er

cong

estio

n w

indo

w s

ize


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwndRTT

bytessec






Host A

RTT

Host B

time



















cwnd gt ssthresh

congestionavoidance



new ACK


fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


WRTT bytessec










TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R






















linkphysical


linkphysical

ECN=00 ECN=11

ECE=1

IP datagram

TCP ACK segment






bull UDPbull TCP

next leaving the




sender receiver

rcv pkt1

rcv pkt0

send ack0

send ack1

send ack0

rcv ack0

send pkt0

send pkt1

rcv ack1

send pkt0rcv pkt0

pkt0

pkt0

pkt1

ack1

ack0

ack0

(a) no loss

sender receiver

rcv pkt1

rcv pkt0

send ack0

send ack1

send ack0

rcv ack0

send pkt0

send pkt1

rcv ack1

send pkt0rcv pkt0

pkt0

pkt0

ack1

ack0

ack0

(b) packet loss

pkt1X

loss

pkt1timeout

resend pkt1

rdt30 in action


rdt30 in action

rcv pkt1send ack1

(detect duplicate)

pkt1

sender receiver

rcv pkt1

rcv pkt0

send ack0

send ack1

send ack0

rcv ack0

send pkt0

send pkt1

rcv ack1

send pkt0rcv pkt0

pkt0

pkt0

ack1

ack0

ack0

(c) ACK loss

ack1X

loss

pkt1timeout

resend pkt1

rcv pkt1send ack1

(detect duplicate)

pkt1

sender receiver

rcv pkt1

send ack0rcv ack0

send pkt1

send pkt0rcv pkt0

pkt0

ack0


pkt1timeout

resend pkt1

ack1

send ack1

send pkt0rcv ack1

pkt0

ack1

ack0






packet


U sender =

008 30008

= 000027 L R RTT + L R

=



Dtrans = LR





sender receiver

RTT




U sender =

008 30008

= 000027 L R RTT + L R

=








RTT






U sender =

0024 30008

= 000081 3L R RTT + L R

=










ack for each packet







window




timeout

rdt_send(data)







base=1nextseqnum=1






Wait







GBN in action


(wait)

sender receiver



rcv ack1 send pkt5


Xloss





0 1 2 3 4 5 6 7 8

sender window (N=4)

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8










Selective repeat



timerACK(n) in








receiver




(wait)

sender receiver



rcv ack1 send pkt5


Xloss




record ack3 arrived

0 1 2 3 4 5 6 7 8

sender window (N=4)

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8







0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2

pkt0pkt1pkt2

0 1 2 3 0 1 2 pkt0


0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2XXX


0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2

pkt0pkt1pkt2

0 1 2 3 0 1 2pkt0

0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2


0 1 2 3 0 1 2 pkt3

(a) no problem















control









overwhelm receiver









32 bits

applicationdata

(variable length)


receive window


lennot

used



ACK ACK valid



commands)



Internetchecksum

(as in UDP)








checksum

rwndurg pointer


A

sent ACKed



not usable

window sizeN




checksum

rwndurg pointer





host ACKsreceipt




Host BHost A



Seq=43 ACK=80














100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106time (seconnds)

RTT

(mill

iseco

nds)






T (m

illise

cond

s)



time (seconds)






(typically = 025)













control









congestion control















waitfor

event



start timer



start timer

timeout






lost ACK scenario

Host BHost A


ACK=100


Xtimeo

ut

ACK=100

premature timeout

Host BHost A


ACK=100


timeo

ut

ACK=120


ACK=120

SendBase=100

SendBase=120

SendBase=120

SendBase=92



X

cumulative ACK

Host BHost A


ACK=100


timeo

ut


ACK=120



event at receiver





TCP receiver action














TCP fast retransmit



X


Host BHost A


ACK=100

timeo

ut ACK=100

ACK=100ACK=100

TCP fast retransmit












control



process


TCPcode

IPcode

applicationOS





from sender


flow control


TCP flow control

buffered data


RcvBuffer


















control








application

network




application

network








2-way handshake

Letrsquos talk

OKESTAB

ESTAB


ESTABacc_conn(x)





ESTAB

req_conn(x)


client terminates

serverforgets x



ESTAB

req_conn(x)

data(x+1)

retransmitdata(x+1)

acceptdata(x+1)

choose xreq_conn(x)

ESTAB

ESTAB

acc_conn(x)

client terminates

ESTAB

choose xreq_conn(x)

ESTABacc_conn(x)



forgets x


TCP 3-way handshake

SYNbit=1 Seq=x


ESTAB



ACKbit=1 ACKnum=y+1




SYNSENT

ESTAB

SYN RCVD

client stateLISTEN

server stateLISTEN



closed

listen

SYNrcvd

SYNsent

ESTAB


SYN(seq=x)











FIN_WAIT_2

CLOSE_WAIT

FINbit=1 seq=y

ACKbit=1 ACKnum=y+1


close

can stillsend data


LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2max

segment lifetime

CLOSED



clientSocketclose()











control





a top-10 problem








Host A

original data in

Host B

throughput out

R2

R2

out

in R2de

lay








Host A

in original data

Host B


lsquo








free buffer space

R2

R2

out

in


Host B

A




no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







rsquo increase


Host A out


Host B

Host CHost D


retransmitted data







C2

C2

out

inrsquo










control





loss

cwnd

TCP

send

er

cong

estio

n w

indo

w s

ize


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwndRTT

bytessec






Host A

RTT

Host B

time



















cwnd gt ssthresh

congestionavoidance



new ACK


fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


WRTT bytessec










TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R






















linkphysical


linkphysical

ECN=00 ECN=11

ECE=1

IP datagram

TCP ACK segment






bull UDPbull TCP

next leaving the




rdt30 in action

rcv pkt1send ack1

(detect duplicate)

pkt1

sender receiver

rcv pkt1

rcv pkt0

send ack0

send ack1

send ack0

rcv ack0

send pkt0

send pkt1

rcv ack1

send pkt0rcv pkt0

pkt0

pkt0

ack1

ack0

ack0

(c) ACK loss

ack1X

loss

pkt1timeout

resend pkt1

rcv pkt1send ack1

(detect duplicate)

pkt1

sender receiver

rcv pkt1

send ack0rcv ack0

send pkt1

send pkt0rcv pkt0

pkt0

ack0


pkt1timeout

resend pkt1

ack1

send ack1

send pkt0rcv ack1

pkt0

ack1

ack0






packet


U sender =

008 30008

= 000027 L R RTT + L R

=



Dtrans = LR





sender receiver

RTT




U sender =

008 30008

= 000027 L R RTT + L R

=








RTT






U sender =

0024 30008

= 000081 3L R RTT + L R

=










ack for each packet







window




timeout

rdt_send(data)







base=1nextseqnum=1






Wait







GBN in action


(wait)

sender receiver



rcv ack1 send pkt5


Xloss





0 1 2 3 4 5 6 7 8

sender window (N=4)

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8










Selective repeat



timerACK(n) in








receiver




(wait)

sender receiver



rcv ack1 send pkt5


Xloss




record ack3 arrived

0 1 2 3 4 5 6 7 8

sender window (N=4)

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8







0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2

pkt0pkt1pkt2

0 1 2 3 0 1 2 pkt0


0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2XXX


0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2

pkt0pkt1pkt2

0 1 2 3 0 1 2pkt0

0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2


0 1 2 3 0 1 2 pkt3

(a) no problem















control









overwhelm receiver









32 bits

applicationdata

(variable length)


receive window


lennot

used



ACK ACK valid



commands)



Internetchecksum

(as in UDP)








checksum

rwndurg pointer


A

sent ACKed



not usable

window sizeN




checksum

rwndurg pointer





host ACKsreceipt




Host BHost A



Seq=43 ACK=80














100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106time (seconnds)

RTT

(mill

iseco

nds)






T (m

illise

cond

s)



time (seconds)






(typically = 025)













control









congestion control















waitfor

event



start timer



start timer

timeout






lost ACK scenario

Host BHost A


ACK=100


Xtimeo

ut

ACK=100

premature timeout

Host BHost A


ACK=100


timeo

ut

ACK=120


ACK=120

SendBase=100

SendBase=120

SendBase=120

SendBase=92



X

cumulative ACK

Host BHost A


ACK=100


timeo

ut


ACK=120



event at receiver





TCP receiver action














TCP fast retransmit



X


Host BHost A


ACK=100

timeo

ut ACK=100

ACK=100ACK=100

TCP fast retransmit












control



process


TCPcode

IPcode

applicationOS





from sender


flow control


TCP flow control

buffered data


RcvBuffer


















control








application

network




application

network








2-way handshake

Letrsquos talk

OKESTAB

ESTAB


ESTABacc_conn(x)





ESTAB

req_conn(x)


client terminates

serverforgets x



ESTAB

req_conn(x)

data(x+1)

retransmitdata(x+1)

acceptdata(x+1)

choose xreq_conn(x)

ESTAB

ESTAB

acc_conn(x)

client terminates

ESTAB

choose xreq_conn(x)

ESTABacc_conn(x)



forgets x


TCP 3-way handshake

SYNbit=1 Seq=x


ESTAB



ACKbit=1 ACKnum=y+1




SYNSENT

ESTAB

SYN RCVD

client stateLISTEN

server stateLISTEN



closed

listen

SYNrcvd

SYNsent

ESTAB


SYN(seq=x)











FIN_WAIT_2

CLOSE_WAIT

FINbit=1 seq=y

ACKbit=1 ACKnum=y+1


close

can stillsend data


LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2max

segment lifetime

CLOSED



clientSocketclose()











control





a top-10 problem








Host A

original data in

Host B

throughput out

R2

R2

out

in R2de

lay








Host A

in original data

Host B


lsquo








free buffer space

R2

R2

out

in


Host B

A




no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







rsquo increase


Host A out


Host B

Host CHost D


retransmitted data







C2

C2

out

inrsquo










control





loss

cwnd

TCP

send

er

cong

estio

n w

indo

w s

ize


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwndRTT

bytessec






Host A

RTT

Host B

time



















cwnd gt ssthresh

congestionavoidance



new ACK


fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


WRTT bytessec










TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R






















linkphysical


linkphysical

ECN=00 ECN=11

ECE=1

IP datagram

TCP ACK segment






bull UDPbull TCP

next leaving the





packet


U sender =

008 30008

= 000027 L R RTT + L R

=



Dtrans = LR





sender receiver

RTT




U sender =

008 30008

= 000027 L R RTT + L R

=








RTT






U sender =

0024 30008

= 000081 3L R RTT + L R

=










ack for each packet







window




timeout

rdt_send(data)







base=1nextseqnum=1






Wait







GBN in action


(wait)

sender receiver



rcv ack1 send pkt5


Xloss





0 1 2 3 4 5 6 7 8

sender window (N=4)

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8










Selective repeat



timerACK(n) in








receiver




(wait)

sender receiver



rcv ack1 send pkt5


Xloss




record ack3 arrived

0 1 2 3 4 5 6 7 8

sender window (N=4)

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8







0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2

pkt0pkt1pkt2

0 1 2 3 0 1 2 pkt0


0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2XXX


0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2

pkt0pkt1pkt2

0 1 2 3 0 1 2pkt0

0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2


0 1 2 3 0 1 2 pkt3

(a) no problem















control









overwhelm receiver









32 bits

applicationdata

(variable length)


receive window


lennot

used



ACK ACK valid



commands)



Internetchecksum

(as in UDP)








checksum

rwndurg pointer


A

sent ACKed



not usable

window sizeN




checksum

rwndurg pointer





host ACKsreceipt




Host BHost A



Seq=43 ACK=80














100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106time (seconnds)

RTT

(mill

iseco

nds)






T (m

illise

cond

s)



time (seconds)






(typically = 025)













control









congestion control















waitfor

event



start timer



start timer

timeout






lost ACK scenario

Host BHost A


ACK=100


Xtimeo

ut

ACK=100

premature timeout

Host BHost A


ACK=100


timeo

ut

ACK=120


ACK=120

SendBase=100

SendBase=120

SendBase=120

SendBase=92



X

cumulative ACK

Host BHost A


ACK=100


timeo

ut


ACK=120



event at receiver





TCP receiver action














TCP fast retransmit



X


Host BHost A


ACK=100

timeo

ut ACK=100

ACK=100ACK=100

TCP fast retransmit












control



process


TCPcode

IPcode

applicationOS





from sender


flow control


TCP flow control

buffered data


RcvBuffer


















control








application

network




application

network








2-way handshake

Letrsquos talk

OKESTAB

ESTAB


ESTABacc_conn(x)





ESTAB

req_conn(x)


client terminates

serverforgets x



ESTAB

req_conn(x)

data(x+1)

retransmitdata(x+1)

acceptdata(x+1)

choose xreq_conn(x)

ESTAB

ESTAB

acc_conn(x)

client terminates

ESTAB

choose xreq_conn(x)

ESTABacc_conn(x)



forgets x


TCP 3-way handshake

SYNbit=1 Seq=x


ESTAB



ACKbit=1 ACKnum=y+1




SYNSENT

ESTAB

SYN RCVD

client stateLISTEN

server stateLISTEN



closed

listen

SYNrcvd

SYNsent

ESTAB


SYN(seq=x)











FIN_WAIT_2

CLOSE_WAIT

FINbit=1 seq=y

ACKbit=1 ACKnum=y+1


close

can stillsend data


LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2max

segment lifetime

CLOSED



clientSocketclose()











control





a top-10 problem








Host A

original data in

Host B

throughput out

R2

R2

out

in R2de

lay








Host A

in original data

Host B


lsquo








free buffer space

R2

R2

out

in


Host B

A




no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







rsquo increase


Host A out


Host B

Host CHost D


retransmitted data







C2

C2

out

inrsquo










control





loss

cwnd

TCP

send

er

cong

estio

n w

indo

w s

ize


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwndRTT

bytessec






Host A

RTT

Host B

time



















cwnd gt ssthresh

congestionavoidance



new ACK


fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


WRTT bytessec










TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R






















linkphysical


linkphysical

ECN=00 ECN=11

ECE=1

IP datagram

TCP ACK segment






bull UDPbull TCP

next leaving the






sender receiver

RTT




U sender =

008 30008

= 000027 L R RTT + L R

=








RTT






U sender =

0024 30008

= 000081 3L R RTT + L R

=










ack for each packet







window




timeout

rdt_send(data)







base=1nextseqnum=1






Wait







GBN in action


(wait)

sender receiver



rcv ack1 send pkt5


Xloss





0 1 2 3 4 5 6 7 8

sender window (N=4)

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8










Selective repeat



timerACK(n) in








receiver




(wait)

sender receiver



rcv ack1 send pkt5


Xloss




record ack3 arrived

0 1 2 3 4 5 6 7 8

sender window (N=4)

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8







0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2

pkt0pkt1pkt2

0 1 2 3 0 1 2 pkt0


0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2XXX


0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2

pkt0pkt1pkt2

0 1 2 3 0 1 2pkt0

0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2


0 1 2 3 0 1 2 pkt3

(a) no problem















control









overwhelm receiver









32 bits

applicationdata

(variable length)


receive window


lennot

used



ACK ACK valid



commands)



Internetchecksum

(as in UDP)








checksum

rwndurg pointer


A

sent ACKed



not usable

window sizeN




checksum

rwndurg pointer





host ACKsreceipt




Host BHost A



Seq=43 ACK=80














100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106time (seconnds)

RTT

(mill

iseco

nds)






T (m

illise

cond

s)



time (seconds)






(typically = 025)













control









congestion control















waitfor

event



start timer



start timer

timeout






lost ACK scenario

Host BHost A


ACK=100


Xtimeo

ut

ACK=100

premature timeout

Host BHost A


ACK=100


timeo

ut

ACK=120


ACK=120

SendBase=100

SendBase=120

SendBase=120

SendBase=92



X

cumulative ACK

Host BHost A


ACK=100


timeo

ut


ACK=120



event at receiver





TCP receiver action














TCP fast retransmit



X


Host BHost A


ACK=100

timeo

ut ACK=100

ACK=100ACK=100

TCP fast retransmit












control



process


TCPcode

IPcode

applicationOS





from sender


flow control


TCP flow control

buffered data


RcvBuffer


















control








application

network




application

network








2-way handshake

Letrsquos talk

OKESTAB

ESTAB


ESTABacc_conn(x)





ESTAB

req_conn(x)


client terminates

serverforgets x



ESTAB

req_conn(x)

data(x+1)

retransmitdata(x+1)

acceptdata(x+1)

choose xreq_conn(x)

ESTAB

ESTAB

acc_conn(x)

client terminates

ESTAB

choose xreq_conn(x)

ESTABacc_conn(x)



forgets x


TCP 3-way handshake

SYNbit=1 Seq=x


ESTAB



ACKbit=1 ACKnum=y+1




SYNSENT

ESTAB

SYN RCVD

client stateLISTEN

server stateLISTEN



closed

listen

SYNrcvd

SYNsent

ESTAB


SYN(seq=x)











FIN_WAIT_2

CLOSE_WAIT

FINbit=1 seq=y

ACKbit=1 ACKnum=y+1


close

can stillsend data


LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2max

segment lifetime

CLOSED



clientSocketclose()











control





a top-10 problem








Host A

original data in

Host B

throughput out

R2

R2

out

in R2de

lay








Host A

in original data

Host B


lsquo








free buffer space

R2

R2

out

in


Host B

A




no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







rsquo increase


Host A out


Host B

Host CHost D


retransmitted data







C2

C2

out

inrsquo










control





loss

cwnd

TCP

send

er

cong

estio

n w

indo

w s

ize


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwndRTT

bytessec






Host A

RTT

Host B

time



















cwnd gt ssthresh

congestionavoidance



new ACK


fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


WRTT bytessec










TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R






















linkphysical


linkphysical

ECN=00 ECN=11

ECE=1

IP datagram

TCP ACK segment






bull UDPbull TCP

next leaving the










RTT






U sender =

0024 30008

= 000081 3L R RTT + L R

=










ack for each packet







window




timeout

rdt_send(data)







base=1nextseqnum=1






Wait







GBN in action


(wait)

sender receiver



rcv ack1 send pkt5


Xloss





0 1 2 3 4 5 6 7 8

sender window (N=4)

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8










Selective repeat



timerACK(n) in








receiver




(wait)

sender receiver



rcv ack1 send pkt5


Xloss




record ack3 arrived

0 1 2 3 4 5 6 7 8

sender window (N=4)

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8







0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2

pkt0pkt1pkt2

0 1 2 3 0 1 2 pkt0


0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2XXX


0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2

pkt0pkt1pkt2

0 1 2 3 0 1 2pkt0

0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2


0 1 2 3 0 1 2 pkt3

(a) no problem















control









overwhelm receiver









32 bits

applicationdata

(variable length)


receive window


lennot

used



ACK ACK valid



commands)



Internetchecksum

(as in UDP)








checksum

rwndurg pointer


A

sent ACKed



not usable

window sizeN




checksum

rwndurg pointer





host ACKsreceipt




Host BHost A



Seq=43 ACK=80














100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106time (seconnds)

RTT

(mill

iseco

nds)






T (m

illise

cond

s)



time (seconds)






(typically = 025)













control









congestion control















waitfor

event



start timer



start timer

timeout






lost ACK scenario

Host BHost A


ACK=100


Xtimeo

ut

ACK=100

premature timeout

Host BHost A


ACK=100


timeo

ut

ACK=120


ACK=120

SendBase=100

SendBase=120

SendBase=120

SendBase=92



X

cumulative ACK

Host BHost A


ACK=100


timeo

ut


ACK=120



event at receiver





TCP receiver action














TCP fast retransmit



X


Host BHost A


ACK=100

timeo

ut ACK=100

ACK=100ACK=100

TCP fast retransmit












control



process


TCPcode

IPcode

applicationOS





from sender


flow control


TCP flow control

buffered data


RcvBuffer


















control








application

network




application

network








2-way handshake

Letrsquos talk

OKESTAB

ESTAB


ESTABacc_conn(x)





ESTAB

req_conn(x)


client terminates

serverforgets x



ESTAB

req_conn(x)

data(x+1)

retransmitdata(x+1)

acceptdata(x+1)

choose xreq_conn(x)

ESTAB

ESTAB

acc_conn(x)

client terminates

ESTAB

choose xreq_conn(x)

ESTABacc_conn(x)



forgets x


TCP 3-way handshake

SYNbit=1 Seq=x


ESTAB



ACKbit=1 ACKnum=y+1




SYNSENT

ESTAB

SYN RCVD

client stateLISTEN

server stateLISTEN



closed

listen

SYNrcvd

SYNsent

ESTAB


SYN(seq=x)











FIN_WAIT_2

CLOSE_WAIT

FINbit=1 seq=y

ACKbit=1 ACKnum=y+1


close

can stillsend data


LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2max

segment lifetime

CLOSED



clientSocketclose()











control





a top-10 problem








Host A

original data in

Host B

throughput out

R2

R2

out

in R2de

lay








Host A

in original data

Host B


lsquo








free buffer space

R2

R2

out

in


Host B

A




no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







rsquo increase


Host A out


Host B

Host CHost D


retransmitted data







C2

C2

out

inrsquo










control





loss

cwnd

TCP

send

er

cong

estio

n w

indo

w s

ize


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwndRTT

bytessec






Host A

RTT

Host B

time



















cwnd gt ssthresh

congestionavoidance



new ACK


fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


WRTT bytessec










TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R






















linkphysical


linkphysical

ECN=00 ECN=11

ECE=1

IP datagram

TCP ACK segment






bull UDPbull TCP

next leaving the












ack for each packet







window




timeout

rdt_send(data)







base=1nextseqnum=1






Wait







GBN in action


(wait)

sender receiver



rcv ack1 send pkt5


Xloss





0 1 2 3 4 5 6 7 8

sender window (N=4)

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8










Selective repeat



timerACK(n) in








receiver




(wait)

sender receiver



rcv ack1 send pkt5


Xloss




record ack3 arrived

0 1 2 3 4 5 6 7 8

sender window (N=4)

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8







0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2

pkt0pkt1pkt2

0 1 2 3 0 1 2 pkt0


0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2XXX


0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2

pkt0pkt1pkt2

0 1 2 3 0 1 2pkt0

0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2


0 1 2 3 0 1 2 pkt3

(a) no problem















control









overwhelm receiver









32 bits

applicationdata

(variable length)


receive window


lennot

used



ACK ACK valid



commands)



Internetchecksum

(as in UDP)








checksum

rwndurg pointer


A

sent ACKed



not usable

window sizeN




checksum

rwndurg pointer





host ACKsreceipt




Host BHost A



Seq=43 ACK=80














100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106time (seconnds)

RTT

(mill

iseco

nds)






T (m

illise

cond

s)



time (seconds)






(typically = 025)













control









congestion control















waitfor

event



start timer



start timer

timeout






lost ACK scenario

Host BHost A


ACK=100


Xtimeo

ut

ACK=100

premature timeout

Host BHost A


ACK=100


timeo

ut

ACK=120


ACK=120

SendBase=100

SendBase=120

SendBase=120

SendBase=92



X

cumulative ACK

Host BHost A


ACK=100


timeo

ut


ACK=120



event at receiver





TCP receiver action














TCP fast retransmit



X


Host BHost A


ACK=100

timeo

ut ACK=100

ACK=100ACK=100

TCP fast retransmit












control



process


TCPcode

IPcode

applicationOS





from sender


flow control


TCP flow control

buffered data


RcvBuffer


















control








application

network




application

network








2-way handshake

Letrsquos talk

OKESTAB

ESTAB


ESTABacc_conn(x)





ESTAB

req_conn(x)


client terminates

serverforgets x



ESTAB

req_conn(x)

data(x+1)

retransmitdata(x+1)

acceptdata(x+1)

choose xreq_conn(x)

ESTAB

ESTAB

acc_conn(x)

client terminates

ESTAB

choose xreq_conn(x)

ESTABacc_conn(x)



forgets x


TCP 3-way handshake

SYNbit=1 Seq=x


ESTAB



ACKbit=1 ACKnum=y+1




SYNSENT

ESTAB

SYN RCVD

client stateLISTEN

server stateLISTEN



closed

listen

SYNrcvd

SYNsent

ESTAB


SYN(seq=x)











FIN_WAIT_2

CLOSE_WAIT

FINbit=1 seq=y

ACKbit=1 ACKnum=y+1


close

can stillsend data


LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2max

segment lifetime

CLOSED



clientSocketclose()











control





a top-10 problem








Host A

original data in

Host B

throughput out

R2

R2

out

in R2de

lay








Host A

in original data

Host B


lsquo








free buffer space

R2

R2

out

in


Host B

A




no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







rsquo increase


Host A out


Host B

Host CHost D


retransmitted data







C2

C2

out

inrsquo










control





loss

cwnd

TCP

send

er

cong

estio

n w

indo

w s

ize


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwndRTT

bytessec






Host A

RTT

Host B

time



















cwnd gt ssthresh

congestionavoidance



new ACK


fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


WRTT bytessec










TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R






















linkphysical


linkphysical

ECN=00 ECN=11

ECE=1

IP datagram

TCP ACK segment






bull UDPbull TCP

next leaving the







window




timeout

rdt_send(data)







base=1nextseqnum=1






Wait







GBN in action


(wait)

sender receiver



rcv ack1 send pkt5


Xloss





0 1 2 3 4 5 6 7 8

sender window (N=4)

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8










Selective repeat



timerACK(n) in








receiver




(wait)

sender receiver



rcv ack1 send pkt5


Xloss




record ack3 arrived

0 1 2 3 4 5 6 7 8

sender window (N=4)

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8







0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2

pkt0pkt1pkt2

0 1 2 3 0 1 2 pkt0


0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2XXX


0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2

pkt0pkt1pkt2

0 1 2 3 0 1 2pkt0

0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2


0 1 2 3 0 1 2 pkt3

(a) no problem















control









overwhelm receiver









32 bits

applicationdata

(variable length)


receive window


lennot

used



ACK ACK valid



commands)



Internetchecksum

(as in UDP)








checksum

rwndurg pointer


A

sent ACKed



not usable

window sizeN




checksum

rwndurg pointer





host ACKsreceipt




Host BHost A



Seq=43 ACK=80














100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106time (seconnds)

RTT

(mill

iseco

nds)






T (m

illise

cond

s)



time (seconds)






(typically = 025)













control









congestion control















waitfor

event



start timer



start timer

timeout






lost ACK scenario

Host BHost A


ACK=100


Xtimeo

ut

ACK=100

premature timeout

Host BHost A


ACK=100


timeo

ut

ACK=120


ACK=120

SendBase=100

SendBase=120

SendBase=120

SendBase=92



X

cumulative ACK

Host BHost A


ACK=100


timeo

ut


ACK=120



event at receiver





TCP receiver action














TCP fast retransmit



X


Host BHost A


ACK=100

timeo

ut ACK=100

ACK=100ACK=100

TCP fast retransmit












control



process


TCPcode

IPcode

applicationOS





from sender


flow control


TCP flow control

buffered data


RcvBuffer


















control








application

network




application

network








2-way handshake

Letrsquos talk

OKESTAB

ESTAB


ESTABacc_conn(x)





ESTAB

req_conn(x)


client terminates

serverforgets x



ESTAB

req_conn(x)

data(x+1)

retransmitdata(x+1)

acceptdata(x+1)

choose xreq_conn(x)

ESTAB

ESTAB

acc_conn(x)

client terminates

ESTAB

choose xreq_conn(x)

ESTABacc_conn(x)



forgets x


TCP 3-way handshake

SYNbit=1 Seq=x


ESTAB



ACKbit=1 ACKnum=y+1




SYNSENT

ESTAB

SYN RCVD

client stateLISTEN

server stateLISTEN



closed

listen

SYNrcvd

SYNsent

ESTAB


SYN(seq=x)











FIN_WAIT_2

CLOSE_WAIT

FINbit=1 seq=y

ACKbit=1 ACKnum=y+1


close

can stillsend data


LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2max

segment lifetime

CLOSED



clientSocketclose()











control





a top-10 problem








Host A

original data in

Host B

throughput out

R2

R2

out

in R2de

lay








Host A

in original data

Host B


lsquo








free buffer space

R2

R2

out

in


Host B

A




no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







rsquo increase


Host A out


Host B

Host CHost D


retransmitted data







C2

C2

out

inrsquo










control





loss

cwnd

TCP

send

er

cong

estio

n w

indo

w s

ize


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwndRTT

bytessec






Host A

RTT

Host B

time



















cwnd gt ssthresh

congestionavoidance



new ACK


fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


WRTT bytessec










TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R






















linkphysical


linkphysical

ECN=00 ECN=11

ECE=1

IP datagram

TCP ACK segment






bull UDPbull TCP

next leaving the






timeout

rdt_send(data)







base=1nextseqnum=1






Wait







GBN in action


(wait)

sender receiver



rcv ack1 send pkt5


Xloss





0 1 2 3 4 5 6 7 8

sender window (N=4)

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8










Selective repeat



timerACK(n) in








receiver




(wait)

sender receiver



rcv ack1 send pkt5


Xloss




record ack3 arrived

0 1 2 3 4 5 6 7 8

sender window (N=4)

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8







0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2

pkt0pkt1pkt2

0 1 2 3 0 1 2 pkt0


0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2XXX


0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2

pkt0pkt1pkt2

0 1 2 3 0 1 2pkt0

0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2


0 1 2 3 0 1 2 pkt3

(a) no problem















control









overwhelm receiver









32 bits

applicationdata

(variable length)


receive window


lennot

used



ACK ACK valid



commands)



Internetchecksum

(as in UDP)








checksum

rwndurg pointer


A

sent ACKed



not usable

window sizeN




checksum

rwndurg pointer





host ACKsreceipt




Host BHost A



Seq=43 ACK=80














100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106time (seconnds)

RTT

(mill

iseco

nds)






T (m

illise

cond

s)



time (seconds)






(typically = 025)













control









congestion control















waitfor

event



start timer



start timer

timeout






lost ACK scenario

Host BHost A


ACK=100


Xtimeo

ut

ACK=100

premature timeout

Host BHost A


ACK=100


timeo

ut

ACK=120


ACK=120

SendBase=100

SendBase=120

SendBase=120

SendBase=92



X

cumulative ACK

Host BHost A


ACK=100


timeo

ut


ACK=120



event at receiver





TCP receiver action














TCP fast retransmit



X


Host BHost A


ACK=100

timeo

ut ACK=100

ACK=100ACK=100

TCP fast retransmit












control



process


TCPcode

IPcode

applicationOS





from sender


flow control


TCP flow control

buffered data


RcvBuffer


















control








application

network




application

network








2-way handshake

Letrsquos talk

OKESTAB

ESTAB


ESTABacc_conn(x)





ESTAB

req_conn(x)


client terminates

serverforgets x



ESTAB

req_conn(x)

data(x+1)

retransmitdata(x+1)

acceptdata(x+1)

choose xreq_conn(x)

ESTAB

ESTAB

acc_conn(x)

client terminates

ESTAB

choose xreq_conn(x)

ESTABacc_conn(x)



forgets x


TCP 3-way handshake

SYNbit=1 Seq=x


ESTAB



ACKbit=1 ACKnum=y+1




SYNSENT

ESTAB

SYN RCVD

client stateLISTEN

server stateLISTEN



closed

listen

SYNrcvd

SYNsent

ESTAB


SYN(seq=x)











FIN_WAIT_2

CLOSE_WAIT

FINbit=1 seq=y

ACKbit=1 ACKnum=y+1


close

can stillsend data


LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2max

segment lifetime

CLOSED



clientSocketclose()











control





a top-10 problem








Host A

original data in

Host B

throughput out

R2

R2

out

in R2de

lay








Host A

in original data

Host B


lsquo








free buffer space

R2

R2

out

in


Host B

A




no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







rsquo increase


Host A out


Host B

Host CHost D


retransmitted data







C2

C2

out

inrsquo










control





loss

cwnd

TCP

send

er

cong

estio

n w

indo

w s

ize


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwndRTT

bytessec






Host A

RTT

Host B

time



















cwnd gt ssthresh

congestionavoidance



new ACK


fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


WRTT bytessec










TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R






















linkphysical


linkphysical

ECN=00 ECN=11

ECE=1

IP datagram

TCP ACK segment






bull UDPbull TCP

next leaving the







Wait







GBN in action


(wait)

sender receiver



rcv ack1 send pkt5


Xloss





0 1 2 3 4 5 6 7 8

sender window (N=4)

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8










Selective repeat



timerACK(n) in








receiver




(wait)

sender receiver



rcv ack1 send pkt5


Xloss




record ack3 arrived

0 1 2 3 4 5 6 7 8

sender window (N=4)

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8







0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2

pkt0pkt1pkt2

0 1 2 3 0 1 2 pkt0


0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2XXX


0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2

pkt0pkt1pkt2

0 1 2 3 0 1 2pkt0

0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2


0 1 2 3 0 1 2 pkt3

(a) no problem















control









overwhelm receiver









32 bits

applicationdata

(variable length)


receive window


lennot

used



ACK ACK valid



commands)



Internetchecksum

(as in UDP)








checksum

rwndurg pointer


A

sent ACKed



not usable

window sizeN




checksum

rwndurg pointer





host ACKsreceipt




Host BHost A



Seq=43 ACK=80














100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106time (seconnds)

RTT

(mill

iseco

nds)






T (m

illise

cond

s)



time (seconds)






(typically = 025)













control









congestion control















waitfor

event



start timer



start timer

timeout






lost ACK scenario

Host BHost A


ACK=100


Xtimeo

ut

ACK=100

premature timeout

Host BHost A


ACK=100


timeo

ut

ACK=120


ACK=120

SendBase=100

SendBase=120

SendBase=120

SendBase=92



X

cumulative ACK

Host BHost A


ACK=100


timeo

ut


ACK=120



event at receiver





TCP receiver action














TCP fast retransmit



X


Host BHost A


ACK=100

timeo

ut ACK=100

ACK=100ACK=100

TCP fast retransmit












control



process


TCPcode

IPcode

applicationOS





from sender


flow control


TCP flow control

buffered data


RcvBuffer


















control








application

network




application

network








2-way handshake

Letrsquos talk

OKESTAB

ESTAB


ESTABacc_conn(x)





ESTAB

req_conn(x)


client terminates

serverforgets x



ESTAB

req_conn(x)

data(x+1)

retransmitdata(x+1)

acceptdata(x+1)

choose xreq_conn(x)

ESTAB

ESTAB

acc_conn(x)

client terminates

ESTAB

choose xreq_conn(x)

ESTABacc_conn(x)



forgets x


TCP 3-way handshake

SYNbit=1 Seq=x


ESTAB



ACKbit=1 ACKnum=y+1




SYNSENT

ESTAB

SYN RCVD

client stateLISTEN

server stateLISTEN



closed

listen

SYNrcvd

SYNsent

ESTAB


SYN(seq=x)











FIN_WAIT_2

CLOSE_WAIT

FINbit=1 seq=y

ACKbit=1 ACKnum=y+1


close

can stillsend data


LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2max

segment lifetime

CLOSED



clientSocketclose()











control





a top-10 problem








Host A

original data in

Host B

throughput out

R2

R2

out

in R2de

lay








Host A

in original data

Host B


lsquo








free buffer space

R2

R2

out

in


Host B

A




no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







rsquo increase


Host A out


Host B

Host CHost D


retransmitted data







C2

C2

out

inrsquo










control





loss

cwnd

TCP

send

er

cong

estio

n w

indo

w s

ize


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwndRTT

bytessec






Host A

RTT

Host B

time



















cwnd gt ssthresh

congestionavoidance



new ACK


fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


WRTT bytessec










TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R






















linkphysical


linkphysical

ECN=00 ECN=11

ECE=1

IP datagram

TCP ACK segment






bull UDPbull TCP

next leaving the




GBN in action


(wait)

sender receiver



rcv ack1 send pkt5


Xloss





0 1 2 3 4 5 6 7 8

sender window (N=4)

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8










Selective repeat



timerACK(n) in








receiver




(wait)

sender receiver



rcv ack1 send pkt5


Xloss




record ack3 arrived

0 1 2 3 4 5 6 7 8

sender window (N=4)

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8







0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2

pkt0pkt1pkt2

0 1 2 3 0 1 2 pkt0


0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2XXX


0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2

pkt0pkt1pkt2

0 1 2 3 0 1 2pkt0

0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2


0 1 2 3 0 1 2 pkt3

(a) no problem















control









overwhelm receiver









32 bits

applicationdata

(variable length)


receive window


lennot

used



ACK ACK valid



commands)



Internetchecksum

(as in UDP)








checksum

rwndurg pointer


A

sent ACKed



not usable

window sizeN




checksum

rwndurg pointer





host ACKsreceipt




Host BHost A



Seq=43 ACK=80














100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106time (seconnds)

RTT

(mill

iseco

nds)






T (m

illise

cond

s)



time (seconds)






(typically = 025)













control









congestion control















waitfor

event



start timer



start timer

timeout






lost ACK scenario

Host BHost A


ACK=100


Xtimeo

ut

ACK=100

premature timeout

Host BHost A


ACK=100


timeo

ut

ACK=120


ACK=120

SendBase=100

SendBase=120

SendBase=120

SendBase=92



X

cumulative ACK

Host BHost A


ACK=100


timeo

ut


ACK=120



event at receiver





TCP receiver action














TCP fast retransmit



X


Host BHost A


ACK=100

timeo

ut ACK=100

ACK=100ACK=100

TCP fast retransmit












control



process


TCPcode

IPcode

applicationOS





from sender


flow control


TCP flow control

buffered data


RcvBuffer


















control








application

network




application

network








2-way handshake

Letrsquos talk

OKESTAB

ESTAB


ESTABacc_conn(x)





ESTAB

req_conn(x)


client terminates

serverforgets x



ESTAB

req_conn(x)

data(x+1)

retransmitdata(x+1)

acceptdata(x+1)

choose xreq_conn(x)

ESTAB

ESTAB

acc_conn(x)

client terminates

ESTAB

choose xreq_conn(x)

ESTABacc_conn(x)



forgets x


TCP 3-way handshake

SYNbit=1 Seq=x


ESTAB



ACKbit=1 ACKnum=y+1




SYNSENT

ESTAB

SYN RCVD

client stateLISTEN

server stateLISTEN



closed

listen

SYNrcvd

SYNsent

ESTAB


SYN(seq=x)











FIN_WAIT_2

CLOSE_WAIT

FINbit=1 seq=y

ACKbit=1 ACKnum=y+1


close

can stillsend data


LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2max

segment lifetime

CLOSED



clientSocketclose()











control





a top-10 problem








Host A

original data in

Host B

throughput out

R2

R2

out

in R2de

lay








Host A

in original data

Host B


lsquo








free buffer space

R2

R2

out

in


Host B

A




no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







rsquo increase


Host A out


Host B

Host CHost D


retransmitted data







C2

C2

out

inrsquo










control





loss

cwnd

TCP

send

er

cong

estio

n w

indo

w s

ize


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwndRTT

bytessec






Host A

RTT

Host B

time



















cwnd gt ssthresh

congestionavoidance



new ACK


fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


WRTT bytessec










TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R






















linkphysical


linkphysical

ECN=00 ECN=11

ECE=1

IP datagram

TCP ACK segment






bull UDPbull TCP

next leaving the












Selective repeat



timerACK(n) in








receiver




(wait)

sender receiver



rcv ack1 send pkt5


Xloss




record ack3 arrived

0 1 2 3 4 5 6 7 8

sender window (N=4)

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8







0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2

pkt0pkt1pkt2

0 1 2 3 0 1 2 pkt0


0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2XXX


0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2

pkt0pkt1pkt2

0 1 2 3 0 1 2pkt0

0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2


0 1 2 3 0 1 2 pkt3

(a) no problem















control









overwhelm receiver









32 bits

applicationdata

(variable length)


receive window


lennot

used



ACK ACK valid



commands)



Internetchecksum

(as in UDP)








checksum

rwndurg pointer


A

sent ACKed



not usable

window sizeN




checksum

rwndurg pointer





host ACKsreceipt




Host BHost A



Seq=43 ACK=80














100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106time (seconnds)

RTT

(mill

iseco

nds)






T (m

illise

cond

s)



time (seconds)






(typically = 025)













control









congestion control















waitfor

event



start timer



start timer

timeout






lost ACK scenario

Host BHost A


ACK=100


Xtimeo

ut

ACK=100

premature timeout

Host BHost A


ACK=100


timeo

ut

ACK=120


ACK=120

SendBase=100

SendBase=120

SendBase=120

SendBase=92



X

cumulative ACK

Host BHost A


ACK=100


timeo

ut


ACK=120



event at receiver





TCP receiver action














TCP fast retransmit



X


Host BHost A


ACK=100

timeo

ut ACK=100

ACK=100ACK=100

TCP fast retransmit












control



process


TCPcode

IPcode

applicationOS





from sender


flow control


TCP flow control

buffered data


RcvBuffer


















control








application

network




application

network








2-way handshake

Letrsquos talk

OKESTAB

ESTAB


ESTABacc_conn(x)





ESTAB

req_conn(x)


client terminates

serverforgets x



ESTAB

req_conn(x)

data(x+1)

retransmitdata(x+1)

acceptdata(x+1)

choose xreq_conn(x)

ESTAB

ESTAB

acc_conn(x)

client terminates

ESTAB

choose xreq_conn(x)

ESTABacc_conn(x)



forgets x


TCP 3-way handshake

SYNbit=1 Seq=x


ESTAB



ACKbit=1 ACKnum=y+1




SYNSENT

ESTAB

SYN RCVD

client stateLISTEN

server stateLISTEN



closed

listen

SYNrcvd

SYNsent

ESTAB


SYN(seq=x)











FIN_WAIT_2

CLOSE_WAIT

FINbit=1 seq=y

ACKbit=1 ACKnum=y+1


close

can stillsend data


LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2max

segment lifetime

CLOSED



clientSocketclose()











control





a top-10 problem








Host A

original data in

Host B

throughput out

R2

R2

out

in R2de

lay








Host A

in original data

Host B


lsquo








free buffer space

R2

R2

out

in


Host B

A




no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







rsquo increase


Host A out


Host B

Host CHost D


retransmitted data







C2

C2

out

inrsquo










control





loss

cwnd

TCP

send

er

cong

estio

n w

indo

w s

ize


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwndRTT

bytessec






Host A

RTT

Host B

time



















cwnd gt ssthresh

congestionavoidance



new ACK


fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


WRTT bytessec










TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R






















linkphysical


linkphysical

ECN=00 ECN=11

ECE=1

IP datagram

TCP ACK segment






bull UDPbull TCP

next leaving the






(wait)

sender receiver



rcv ack1 send pkt5


Xloss




record ack3 arrived

0 1 2 3 4 5 6 7 8

sender window (N=4)

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8







0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2

pkt0pkt1pkt2

0 1 2 3 0 1 2 pkt0


0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2XXX


0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2

pkt0pkt1pkt2

0 1 2 3 0 1 2pkt0

0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2


0 1 2 3 0 1 2 pkt3

(a) no problem















control









overwhelm receiver









32 bits

applicationdata

(variable length)


receive window


lennot

used



ACK ACK valid



commands)



Internetchecksum

(as in UDP)








checksum

rwndurg pointer


A

sent ACKed



not usable

window sizeN




checksum

rwndurg pointer





host ACKsreceipt




Host BHost A



Seq=43 ACK=80














100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106time (seconnds)

RTT

(mill

iseco

nds)






T (m

illise

cond

s)



time (seconds)






(typically = 025)













control









congestion control















waitfor

event



start timer



start timer

timeout






lost ACK scenario

Host BHost A


ACK=100


Xtimeo

ut

ACK=100

premature timeout

Host BHost A


ACK=100


timeo

ut

ACK=120


ACK=120

SendBase=100

SendBase=120

SendBase=120

SendBase=92



X

cumulative ACK

Host BHost A


ACK=100


timeo

ut


ACK=120



event at receiver





TCP receiver action














TCP fast retransmit



X


Host BHost A


ACK=100

timeo

ut ACK=100

ACK=100ACK=100

TCP fast retransmit












control



process


TCPcode

IPcode

applicationOS





from sender


flow control


TCP flow control

buffered data


RcvBuffer


















control








application

network




application

network








2-way handshake

Letrsquos talk

OKESTAB

ESTAB


ESTABacc_conn(x)





ESTAB

req_conn(x)


client terminates

serverforgets x



ESTAB

req_conn(x)

data(x+1)

retransmitdata(x+1)

acceptdata(x+1)

choose xreq_conn(x)

ESTAB

ESTAB

acc_conn(x)

client terminates

ESTAB

choose xreq_conn(x)

ESTABacc_conn(x)



forgets x


TCP 3-way handshake

SYNbit=1 Seq=x


ESTAB



ACKbit=1 ACKnum=y+1




SYNSENT

ESTAB

SYN RCVD

client stateLISTEN

server stateLISTEN



closed

listen

SYNrcvd

SYNsent

ESTAB


SYN(seq=x)











FIN_WAIT_2

CLOSE_WAIT

FINbit=1 seq=y

ACKbit=1 ACKnum=y+1


close

can stillsend data


LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2max

segment lifetime

CLOSED



clientSocketclose()











control





a top-10 problem








Host A

original data in

Host B

throughput out

R2

R2

out

in R2de

lay








Host A

in original data

Host B


lsquo








free buffer space

R2

R2

out

in


Host B

A




no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







rsquo increase


Host A out


Host B

Host CHost D


retransmitted data







C2

C2

out

inrsquo










control





loss

cwnd

TCP

send

er

cong

estio

n w

indo

w s

ize


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwndRTT

bytessec






Host A

RTT

Host B

time



















cwnd gt ssthresh

congestionavoidance



new ACK


fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


WRTT bytessec










TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R






















linkphysical


linkphysical

ECN=00 ECN=11

ECE=1

IP datagram

TCP ACK segment






bull UDPbull TCP

next leaving the







0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2

pkt0pkt1pkt2

0 1 2 3 0 1 2 pkt0


0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2XXX


0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2

pkt0pkt1pkt2

0 1 2 3 0 1 2pkt0

0 1 2 3 0 1 2

0 1 2 3 0 1 2

0 1 2 3 0 1 2


0 1 2 3 0 1 2 pkt3

(a) no problem















control









overwhelm receiver









32 bits

applicationdata

(variable length)


receive window


lennot

used



ACK ACK valid



commands)



Internetchecksum

(as in UDP)








checksum

rwndurg pointer


A

sent ACKed



not usable

window sizeN




checksum

rwndurg pointer





host ACKsreceipt




Host BHost A



Seq=43 ACK=80














100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106time (seconnds)

RTT

(mill

iseco

nds)






T (m

illise

cond

s)



time (seconds)






(typically = 025)













control









congestion control















waitfor

event



start timer



start timer

timeout






lost ACK scenario

Host BHost A


ACK=100


Xtimeo

ut

ACK=100

premature timeout

Host BHost A


ACK=100


timeo

ut

ACK=120


ACK=120

SendBase=100

SendBase=120

SendBase=120

SendBase=92



X

cumulative ACK

Host BHost A


ACK=100


timeo

ut


ACK=120



event at receiver





TCP receiver action














TCP fast retransmit



X


Host BHost A


ACK=100

timeo

ut ACK=100

ACK=100ACK=100

TCP fast retransmit












control



process


TCPcode

IPcode

applicationOS





from sender


flow control


TCP flow control

buffered data


RcvBuffer


















control








application

network




application

network








2-way handshake

Letrsquos talk

OKESTAB

ESTAB


ESTABacc_conn(x)





ESTAB

req_conn(x)


client terminates

serverforgets x



ESTAB

req_conn(x)

data(x+1)

retransmitdata(x+1)

acceptdata(x+1)

choose xreq_conn(x)

ESTAB

ESTAB

acc_conn(x)

client terminates

ESTAB

choose xreq_conn(x)

ESTABacc_conn(x)



forgets x


TCP 3-way handshake

SYNbit=1 Seq=x


ESTAB



ACKbit=1 ACKnum=y+1




SYNSENT

ESTAB

SYN RCVD

client stateLISTEN

server stateLISTEN



closed

listen

SYNrcvd

SYNsent

ESTAB


SYN(seq=x)











FIN_WAIT_2

CLOSE_WAIT

FINbit=1 seq=y

ACKbit=1 ACKnum=y+1


close

can stillsend data


LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2max

segment lifetime

CLOSED



clientSocketclose()











control





a top-10 problem








Host A

original data in

Host B

throughput out

R2

R2

out

in R2de

lay








Host A

in original data

Host B


lsquo








free buffer space

R2

R2

out

in


Host B

A




no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







rsquo increase


Host A out


Host B

Host CHost D


retransmitted data







C2

C2

out

inrsquo










control





loss

cwnd

TCP

send

er

cong

estio

n w

indo

w s

ize


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwndRTT

bytessec






Host A

RTT

Host B

time



















cwnd gt ssthresh

congestionavoidance



new ACK


fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


WRTT bytessec










TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R






















linkphysical


linkphysical

ECN=00 ECN=11

ECE=1

IP datagram

TCP ACK segment






bull UDPbull TCP

next leaving the












control









overwhelm receiver









32 bits

applicationdata

(variable length)


receive window


lennot

used



ACK ACK valid



commands)



Internetchecksum

(as in UDP)








checksum

rwndurg pointer


A

sent ACKed



not usable

window sizeN




checksum

rwndurg pointer





host ACKsreceipt




Host BHost A



Seq=43 ACK=80














100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106time (seconnds)

RTT

(mill

iseco

nds)






T (m

illise

cond

s)



time (seconds)






(typically = 025)













control









congestion control















waitfor

event



start timer



start timer

timeout






lost ACK scenario

Host BHost A


ACK=100


Xtimeo

ut

ACK=100

premature timeout

Host BHost A


ACK=100


timeo

ut

ACK=120


ACK=120

SendBase=100

SendBase=120

SendBase=120

SendBase=92



X

cumulative ACK

Host BHost A


ACK=100


timeo

ut


ACK=120



event at receiver





TCP receiver action














TCP fast retransmit



X


Host BHost A


ACK=100

timeo

ut ACK=100

ACK=100ACK=100

TCP fast retransmit












control



process


TCPcode

IPcode

applicationOS





from sender


flow control


TCP flow control

buffered data


RcvBuffer


















control








application

network




application

network








2-way handshake

Letrsquos talk

OKESTAB

ESTAB


ESTABacc_conn(x)





ESTAB

req_conn(x)


client terminates

serverforgets x



ESTAB

req_conn(x)

data(x+1)

retransmitdata(x+1)

acceptdata(x+1)

choose xreq_conn(x)

ESTAB

ESTAB

acc_conn(x)

client terminates

ESTAB

choose xreq_conn(x)

ESTABacc_conn(x)



forgets x


TCP 3-way handshake

SYNbit=1 Seq=x


ESTAB



ACKbit=1 ACKnum=y+1




SYNSENT

ESTAB

SYN RCVD

client stateLISTEN

server stateLISTEN



closed

listen

SYNrcvd

SYNsent

ESTAB


SYN(seq=x)











FIN_WAIT_2

CLOSE_WAIT

FINbit=1 seq=y

ACKbit=1 ACKnum=y+1


close

can stillsend data


LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2max

segment lifetime

CLOSED



clientSocketclose()











control





a top-10 problem








Host A

original data in

Host B

throughput out

R2

R2

out

in R2de

lay








Host A

in original data

Host B


lsquo








free buffer space

R2

R2

out

in


Host B

A




no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







rsquo increase


Host A out


Host B

Host CHost D


retransmitted data







C2

C2

out

inrsquo










control





loss

cwnd

TCP

send

er

cong

estio

n w

indo

w s

ize


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwndRTT

bytessec






Host A

RTT

Host B

time



















cwnd gt ssthresh

congestionavoidance



new ACK


fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


WRTT bytessec










TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R






















linkphysical


linkphysical

ECN=00 ECN=11

ECE=1

IP datagram

TCP ACK segment






bull UDPbull TCP

next leaving the











overwhelm receiver









32 bits

applicationdata

(variable length)


receive window


lennot

used



ACK ACK valid



commands)



Internetchecksum

(as in UDP)








checksum

rwndurg pointer


A

sent ACKed



not usable

window sizeN




checksum

rwndurg pointer





host ACKsreceipt




Host BHost A



Seq=43 ACK=80














100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106time (seconnds)

RTT

(mill

iseco

nds)






T (m

illise

cond

s)



time (seconds)






(typically = 025)













control









congestion control















waitfor

event



start timer



start timer

timeout






lost ACK scenario

Host BHost A


ACK=100


Xtimeo

ut

ACK=100

premature timeout

Host BHost A


ACK=100


timeo

ut

ACK=120


ACK=120

SendBase=100

SendBase=120

SendBase=120

SendBase=92



X

cumulative ACK

Host BHost A


ACK=100


timeo

ut


ACK=120



event at receiver





TCP receiver action














TCP fast retransmit



X


Host BHost A


ACK=100

timeo

ut ACK=100

ACK=100ACK=100

TCP fast retransmit












control



process


TCPcode

IPcode

applicationOS





from sender


flow control


TCP flow control

buffered data


RcvBuffer


















control








application

network




application

network








2-way handshake

Letrsquos talk

OKESTAB

ESTAB


ESTABacc_conn(x)





ESTAB

req_conn(x)


client terminates

serverforgets x



ESTAB

req_conn(x)

data(x+1)

retransmitdata(x+1)

acceptdata(x+1)

choose xreq_conn(x)

ESTAB

ESTAB

acc_conn(x)

client terminates

ESTAB

choose xreq_conn(x)

ESTABacc_conn(x)



forgets x


TCP 3-way handshake

SYNbit=1 Seq=x


ESTAB



ACKbit=1 ACKnum=y+1




SYNSENT

ESTAB

SYN RCVD

client stateLISTEN

server stateLISTEN



closed

listen

SYNrcvd

SYNsent

ESTAB


SYN(seq=x)











FIN_WAIT_2

CLOSE_WAIT

FINbit=1 seq=y

ACKbit=1 ACKnum=y+1


close

can stillsend data


LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2max

segment lifetime

CLOSED



clientSocketclose()











control





a top-10 problem








Host A

original data in

Host B

throughput out

R2

R2

out

in R2de

lay








Host A

in original data

Host B


lsquo








free buffer space

R2

R2

out

in


Host B

A




no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







rsquo increase


Host A out


Host B

Host CHost D


retransmitted data







C2

C2

out

inrsquo










control





loss

cwnd

TCP

send

er

cong

estio

n w

indo

w s

ize


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwndRTT

bytessec






Host A

RTT

Host B

time



















cwnd gt ssthresh

congestionavoidance



new ACK


fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


WRTT bytessec










TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R






















linkphysical


linkphysical

ECN=00 ECN=11

ECE=1

IP datagram

TCP ACK segment






bull UDPbull TCP

next leaving the






32 bits

applicationdata

(variable length)


receive window


lennot

used



ACK ACK valid



commands)



Internetchecksum

(as in UDP)








checksum

rwndurg pointer


A

sent ACKed



not usable

window sizeN




checksum

rwndurg pointer





host ACKsreceipt




Host BHost A



Seq=43 ACK=80














100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106time (seconnds)

RTT

(mill

iseco

nds)






T (m

illise

cond

s)



time (seconds)






(typically = 025)













control









congestion control















waitfor

event



start timer



start timer

timeout






lost ACK scenario

Host BHost A


ACK=100


Xtimeo

ut

ACK=100

premature timeout

Host BHost A


ACK=100


timeo

ut

ACK=120


ACK=120

SendBase=100

SendBase=120

SendBase=120

SendBase=92



X

cumulative ACK

Host BHost A


ACK=100


timeo

ut


ACK=120



event at receiver





TCP receiver action














TCP fast retransmit



X


Host BHost A


ACK=100

timeo

ut ACK=100

ACK=100ACK=100

TCP fast retransmit












control



process


TCPcode

IPcode

applicationOS





from sender


flow control


TCP flow control

buffered data


RcvBuffer


















control








application

network




application

network








2-way handshake

Letrsquos talk

OKESTAB

ESTAB


ESTABacc_conn(x)





ESTAB

req_conn(x)


client terminates

serverforgets x



ESTAB

req_conn(x)

data(x+1)

retransmitdata(x+1)

acceptdata(x+1)

choose xreq_conn(x)

ESTAB

ESTAB

acc_conn(x)

client terminates

ESTAB

choose xreq_conn(x)

ESTABacc_conn(x)



forgets x


TCP 3-way handshake

SYNbit=1 Seq=x


ESTAB



ACKbit=1 ACKnum=y+1




SYNSENT

ESTAB

SYN RCVD

client stateLISTEN

server stateLISTEN



closed

listen

SYNrcvd

SYNsent

ESTAB


SYN(seq=x)











FIN_WAIT_2

CLOSE_WAIT

FINbit=1 seq=y

ACKbit=1 ACKnum=y+1


close

can stillsend data


LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2max

segment lifetime

CLOSED



clientSocketclose()











control





a top-10 problem








Host A

original data in

Host B

throughput out

R2

R2

out

in R2de

lay








Host A

in original data

Host B


lsquo








free buffer space

R2

R2

out

in


Host B

A




no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







rsquo increase


Host A out


Host B

Host CHost D


retransmitted data







C2

C2

out

inrsquo










control





loss

cwnd

TCP

send

er

cong

estio

n w

indo

w s

ize


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwndRTT

bytessec






Host A

RTT

Host B

time



















cwnd gt ssthresh

congestionavoidance



new ACK


fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


WRTT bytessec










TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R






















linkphysical


linkphysical

ECN=00 ECN=11

ECE=1

IP datagram

TCP ACK segment






bull UDPbull TCP

next leaving the










checksum

rwndurg pointer


A

sent ACKed



not usable

window sizeN




checksum

rwndurg pointer





host ACKsreceipt




Host BHost A



Seq=43 ACK=80














100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106time (seconnds)

RTT

(mill

iseco

nds)






T (m

illise

cond

s)



time (seconds)






(typically = 025)













control









congestion control















waitfor

event



start timer



start timer

timeout






lost ACK scenario

Host BHost A


ACK=100


Xtimeo

ut

ACK=100

premature timeout

Host BHost A


ACK=100


timeo

ut

ACK=120


ACK=120

SendBase=100

SendBase=120

SendBase=120

SendBase=92



X

cumulative ACK

Host BHost A


ACK=100


timeo

ut


ACK=120



event at receiver





TCP receiver action














TCP fast retransmit



X


Host BHost A


ACK=100

timeo

ut ACK=100

ACK=100ACK=100

TCP fast retransmit












control



process


TCPcode

IPcode

applicationOS





from sender


flow control


TCP flow control

buffered data


RcvBuffer


















control








application

network




application

network








2-way handshake

Letrsquos talk

OKESTAB

ESTAB


ESTABacc_conn(x)





ESTAB

req_conn(x)


client terminates

serverforgets x



ESTAB

req_conn(x)

data(x+1)

retransmitdata(x+1)

acceptdata(x+1)

choose xreq_conn(x)

ESTAB

ESTAB

acc_conn(x)

client terminates

ESTAB

choose xreq_conn(x)

ESTABacc_conn(x)



forgets x


TCP 3-way handshake

SYNbit=1 Seq=x


ESTAB



ACKbit=1 ACKnum=y+1




SYNSENT

ESTAB

SYN RCVD

client stateLISTEN

server stateLISTEN



closed

listen

SYNrcvd

SYNsent

ESTAB


SYN(seq=x)











FIN_WAIT_2

CLOSE_WAIT

FINbit=1 seq=y

ACKbit=1 ACKnum=y+1


close

can stillsend data


LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2max

segment lifetime

CLOSED



clientSocketclose()











control





a top-10 problem








Host A

original data in

Host B

throughput out

R2

R2

out

in R2de

lay








Host A

in original data

Host B


lsquo








free buffer space

R2

R2

out

in


Host B

A




no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







rsquo increase


Host A out


Host B

Host CHost D


retransmitted data







C2

C2

out

inrsquo










control





loss

cwnd

TCP

send

er

cong

estio

n w

indo

w s

ize


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwndRTT

bytessec






Host A

RTT

Host B

time



















cwnd gt ssthresh

congestionavoidance



new ACK


fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


WRTT bytessec










TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R






















linkphysical


linkphysical

ECN=00 ECN=11

ECE=1

IP datagram

TCP ACK segment






bull UDPbull TCP

next leaving the






host ACKsreceipt




Host BHost A



Seq=43 ACK=80














100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106time (seconnds)

RTT

(mill

iseco

nds)






T (m

illise

cond

s)



time (seconds)






(typically = 025)













control









congestion control















waitfor

event



start timer



start timer

timeout






lost ACK scenario

Host BHost A


ACK=100


Xtimeo

ut

ACK=100

premature timeout

Host BHost A


ACK=100


timeo

ut

ACK=120


ACK=120

SendBase=100

SendBase=120

SendBase=120

SendBase=92



X

cumulative ACK

Host BHost A


ACK=100


timeo

ut


ACK=120



event at receiver





TCP receiver action














TCP fast retransmit



X


Host BHost A


ACK=100

timeo

ut ACK=100

ACK=100ACK=100

TCP fast retransmit












control



process


TCPcode

IPcode

applicationOS





from sender


flow control


TCP flow control

buffered data


RcvBuffer


















control








application

network




application

network








2-way handshake

Letrsquos talk

OKESTAB

ESTAB


ESTABacc_conn(x)





ESTAB

req_conn(x)


client terminates

serverforgets x



ESTAB

req_conn(x)

data(x+1)

retransmitdata(x+1)

acceptdata(x+1)

choose xreq_conn(x)

ESTAB

ESTAB

acc_conn(x)

client terminates

ESTAB

choose xreq_conn(x)

ESTABacc_conn(x)



forgets x


TCP 3-way handshake

SYNbit=1 Seq=x


ESTAB



ACKbit=1 ACKnum=y+1




SYNSENT

ESTAB

SYN RCVD

client stateLISTEN

server stateLISTEN



closed

listen

SYNrcvd

SYNsent

ESTAB


SYN(seq=x)











FIN_WAIT_2

CLOSE_WAIT

FINbit=1 seq=y

ACKbit=1 ACKnum=y+1


close

can stillsend data


LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2max

segment lifetime

CLOSED



clientSocketclose()











control





a top-10 problem








Host A

original data in

Host B

throughput out

R2

R2

out

in R2de

lay








Host A

in original data

Host B


lsquo








free buffer space

R2

R2

out

in


Host B

A




no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







rsquo increase


Host A out


Host B

Host CHost D


retransmitted data







C2

C2

out

inrsquo










control





loss

cwnd

TCP

send

er

cong

estio

n w

indo

w s

ize


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwndRTT

bytessec






Host A

RTT

Host B

time



















cwnd gt ssthresh

congestionavoidance



new ACK


fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


WRTT bytessec










TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R






















linkphysical


linkphysical

ECN=00 ECN=11

ECE=1

IP datagram

TCP ACK segment






bull UDPbull TCP

next leaving the
















100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106time (seconnds)

RTT

(mill

iseco

nds)






T (m

illise

cond

s)



time (seconds)






(typically = 025)













control









congestion control















waitfor

event



start timer



start timer

timeout






lost ACK scenario

Host BHost A


ACK=100


Xtimeo

ut

ACK=100

premature timeout

Host BHost A


ACK=100


timeo

ut

ACK=120


ACK=120

SendBase=100

SendBase=120

SendBase=120

SendBase=92



X

cumulative ACK

Host BHost A


ACK=100


timeo

ut


ACK=120



event at receiver





TCP receiver action














TCP fast retransmit



X


Host BHost A


ACK=100

timeo

ut ACK=100

ACK=100ACK=100

TCP fast retransmit












control



process


TCPcode

IPcode

applicationOS





from sender


flow control


TCP flow control

buffered data


RcvBuffer


















control








application

network




application

network








2-way handshake

Letrsquos talk

OKESTAB

ESTAB


ESTABacc_conn(x)





ESTAB

req_conn(x)


client terminates

serverforgets x



ESTAB

req_conn(x)

data(x+1)

retransmitdata(x+1)

acceptdata(x+1)

choose xreq_conn(x)

ESTAB

ESTAB

acc_conn(x)

client terminates

ESTAB

choose xreq_conn(x)

ESTABacc_conn(x)



forgets x


TCP 3-way handshake

SYNbit=1 Seq=x


ESTAB



ACKbit=1 ACKnum=y+1




SYNSENT

ESTAB

SYN RCVD

client stateLISTEN

server stateLISTEN



closed

listen

SYNrcvd

SYNsent

ESTAB


SYN(seq=x)











FIN_WAIT_2

CLOSE_WAIT

FINbit=1 seq=y

ACKbit=1 ACKnum=y+1


close

can stillsend data


LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2max

segment lifetime

CLOSED



clientSocketclose()











control





a top-10 problem








Host A

original data in

Host B

throughput out

R2

R2

out

in R2de

lay








Host A

in original data

Host B


lsquo








free buffer space

R2

R2

out

in


Host B

A




no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







rsquo increase


Host A out


Host B

Host CHost D


retransmitted data







C2

C2

out

inrsquo










control





loss

cwnd

TCP

send

er

cong

estio

n w

indo

w s

ize


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwndRTT

bytessec






Host A

RTT

Host B

time



















cwnd gt ssthresh

congestionavoidance



new ACK


fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


WRTT bytessec










TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R






















linkphysical


linkphysical

ECN=00 ECN=11

ECE=1

IP datagram

TCP ACK segment






bull UDPbull TCP

next leaving the








(typically = 025)













control









congestion control















waitfor

event



start timer



start timer

timeout






lost ACK scenario

Host BHost A


ACK=100


Xtimeo

ut

ACK=100

premature timeout

Host BHost A


ACK=100


timeo

ut

ACK=120


ACK=120

SendBase=100

SendBase=120

SendBase=120

SendBase=92



X

cumulative ACK

Host BHost A


ACK=100


timeo

ut


ACK=120



event at receiver





TCP receiver action














TCP fast retransmit



X


Host BHost A


ACK=100

timeo

ut ACK=100

ACK=100ACK=100

TCP fast retransmit












control



process


TCPcode

IPcode

applicationOS





from sender


flow control


TCP flow control

buffered data


RcvBuffer


















control








application

network




application

network








2-way handshake

Letrsquos talk

OKESTAB

ESTAB


ESTABacc_conn(x)





ESTAB

req_conn(x)


client terminates

serverforgets x



ESTAB

req_conn(x)

data(x+1)

retransmitdata(x+1)

acceptdata(x+1)

choose xreq_conn(x)

ESTAB

ESTAB

acc_conn(x)

client terminates

ESTAB

choose xreq_conn(x)

ESTABacc_conn(x)



forgets x


TCP 3-way handshake

SYNbit=1 Seq=x


ESTAB



ACKbit=1 ACKnum=y+1




SYNSENT

ESTAB

SYN RCVD

client stateLISTEN

server stateLISTEN



closed

listen

SYNrcvd

SYNsent

ESTAB


SYN(seq=x)











FIN_WAIT_2

CLOSE_WAIT

FINbit=1 seq=y

ACKbit=1 ACKnum=y+1


close

can stillsend data


LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2max

segment lifetime

CLOSED



clientSocketclose()











control





a top-10 problem








Host A

original data in

Host B

throughput out

R2

R2

out

in R2de

lay








Host A

in original data

Host B


lsquo








free buffer space

R2

R2

out

in


Host B

A




no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







rsquo increase


Host A out


Host B

Host CHost D


retransmitted data







C2

C2

out

inrsquo










control





loss

cwnd

TCP

send

er

cong

estio

n w

indo

w s

ize


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwndRTT

bytessec






Host A

RTT

Host B

time



















cwnd gt ssthresh

congestionavoidance



new ACK


fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


WRTT bytessec










TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R






















linkphysical


linkphysical

ECN=00 ECN=11

ECE=1

IP datagram

TCP ACK segment






bull UDPbull TCP

next leaving the












control









congestion control















waitfor

event



start timer



start timer

timeout






lost ACK scenario

Host BHost A


ACK=100


Xtimeo

ut

ACK=100

premature timeout

Host BHost A


ACK=100


timeo

ut

ACK=120


ACK=120

SendBase=100

SendBase=120

SendBase=120

SendBase=92



X

cumulative ACK

Host BHost A


ACK=100


timeo

ut


ACK=120



event at receiver





TCP receiver action














TCP fast retransmit



X


Host BHost A


ACK=100

timeo

ut ACK=100

ACK=100ACK=100

TCP fast retransmit












control



process


TCPcode

IPcode

applicationOS





from sender


flow control


TCP flow control

buffered data


RcvBuffer


















control








application

network




application

network








2-way handshake

Letrsquos talk

OKESTAB

ESTAB


ESTABacc_conn(x)





ESTAB

req_conn(x)


client terminates

serverforgets x



ESTAB

req_conn(x)

data(x+1)

retransmitdata(x+1)

acceptdata(x+1)

choose xreq_conn(x)

ESTAB

ESTAB

acc_conn(x)

client terminates

ESTAB

choose xreq_conn(x)

ESTABacc_conn(x)



forgets x


TCP 3-way handshake

SYNbit=1 Seq=x


ESTAB



ACKbit=1 ACKnum=y+1




SYNSENT

ESTAB

SYN RCVD

client stateLISTEN

server stateLISTEN



closed

listen

SYNrcvd

SYNsent

ESTAB


SYN(seq=x)











FIN_WAIT_2

CLOSE_WAIT

FINbit=1 seq=y

ACKbit=1 ACKnum=y+1


close

can stillsend data


LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2max

segment lifetime

CLOSED



clientSocketclose()











control





a top-10 problem








Host A

original data in

Host B

throughput out

R2

R2

out

in R2de

lay








Host A

in original data

Host B


lsquo








free buffer space

R2

R2

out

in


Host B

A




no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







rsquo increase


Host A out


Host B

Host CHost D


retransmitted data







C2

C2

out

inrsquo










control





loss

cwnd

TCP

send

er

cong

estio

n w

indo

w s

ize


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwndRTT

bytessec






Host A

RTT

Host B

time



















cwnd gt ssthresh

congestionavoidance



new ACK


fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


WRTT bytessec










TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R






















linkphysical


linkphysical

ECN=00 ECN=11

ECE=1

IP datagram

TCP ACK segment






bull UDPbull TCP

next leaving the











congestion control















waitfor

event



start timer



start timer

timeout






lost ACK scenario

Host BHost A


ACK=100


Xtimeo

ut

ACK=100

premature timeout

Host BHost A


ACK=100


timeo

ut

ACK=120


ACK=120

SendBase=100

SendBase=120

SendBase=120

SendBase=92



X

cumulative ACK

Host BHost A


ACK=100


timeo

ut


ACK=120



event at receiver





TCP receiver action














TCP fast retransmit



X


Host BHost A


ACK=100

timeo

ut ACK=100

ACK=100ACK=100

TCP fast retransmit












control



process


TCPcode

IPcode

applicationOS





from sender


flow control


TCP flow control

buffered data


RcvBuffer


















control








application

network




application

network








2-way handshake

Letrsquos talk

OKESTAB

ESTAB


ESTABacc_conn(x)





ESTAB

req_conn(x)


client terminates

serverforgets x



ESTAB

req_conn(x)

data(x+1)

retransmitdata(x+1)

acceptdata(x+1)

choose xreq_conn(x)

ESTAB

ESTAB

acc_conn(x)

client terminates

ESTAB

choose xreq_conn(x)

ESTABacc_conn(x)



forgets x


TCP 3-way handshake

SYNbit=1 Seq=x


ESTAB



ACKbit=1 ACKnum=y+1




SYNSENT

ESTAB

SYN RCVD

client stateLISTEN

server stateLISTEN



closed

listen

SYNrcvd

SYNsent

ESTAB


SYN(seq=x)











FIN_WAIT_2

CLOSE_WAIT

FINbit=1 seq=y

ACKbit=1 ACKnum=y+1


close

can stillsend data


LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2max

segment lifetime

CLOSED



clientSocketclose()











control





a top-10 problem








Host A

original data in

Host B

throughput out

R2

R2

out

in R2de

lay








Host A

in original data

Host B


lsquo








free buffer space

R2

R2

out

in


Host B

A




no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







rsquo increase


Host A out


Host B

Host CHost D


retransmitted data







C2

C2

out

inrsquo










control





loss

cwnd

TCP

send

er

cong

estio

n w

indo

w s

ize


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwndRTT

bytessec






Host A

RTT

Host B

time



















cwnd gt ssthresh

congestionavoidance



new ACK


fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


WRTT bytessec










TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R






















linkphysical


linkphysical

ECN=00 ECN=11

ECE=1

IP datagram

TCP ACK segment






bull UDPbull TCP

next leaving the

















waitfor

event



start timer



start timer

timeout






lost ACK scenario

Host BHost A


ACK=100


Xtimeo

ut

ACK=100

premature timeout

Host BHost A


ACK=100


timeo

ut

ACK=120


ACK=120

SendBase=100

SendBase=120

SendBase=120

SendBase=92



X

cumulative ACK

Host BHost A


ACK=100


timeo

ut


ACK=120



event at receiver





TCP receiver action














TCP fast retransmit



X


Host BHost A


ACK=100

timeo

ut ACK=100

ACK=100ACK=100

TCP fast retransmit












control



process


TCPcode

IPcode

applicationOS





from sender


flow control


TCP flow control

buffered data


RcvBuffer


















control








application

network




application

network








2-way handshake

Letrsquos talk

OKESTAB

ESTAB


ESTABacc_conn(x)





ESTAB

req_conn(x)


client terminates

serverforgets x



ESTAB

req_conn(x)

data(x+1)

retransmitdata(x+1)

acceptdata(x+1)

choose xreq_conn(x)

ESTAB

ESTAB

acc_conn(x)

client terminates

ESTAB

choose xreq_conn(x)

ESTABacc_conn(x)



forgets x


TCP 3-way handshake

SYNbit=1 Seq=x


ESTAB



ACKbit=1 ACKnum=y+1




SYNSENT

ESTAB

SYN RCVD

client stateLISTEN

server stateLISTEN



closed

listen

SYNrcvd

SYNsent

ESTAB


SYN(seq=x)











FIN_WAIT_2

CLOSE_WAIT

FINbit=1 seq=y

ACKbit=1 ACKnum=y+1


close

can stillsend data


LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2max

segment lifetime

CLOSED



clientSocketclose()











control





a top-10 problem








Host A

original data in

Host B

throughput out

R2

R2

out

in R2de

lay








Host A

in original data

Host B


lsquo








free buffer space

R2

R2

out

in


Host B

A




no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







rsquo increase


Host A out


Host B

Host CHost D


retransmitted data







C2

C2

out

inrsquo










control





loss

cwnd

TCP

send

er

cong

estio

n w

indo

w s

ize


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwndRTT

bytessec






Host A

RTT

Host B

time



















cwnd gt ssthresh

congestionavoidance



new ACK


fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


WRTT bytessec










TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R






















linkphysical


linkphysical

ECN=00 ECN=11

ECE=1

IP datagram

TCP ACK segment






bull UDPbull TCP

next leaving the





lost ACK scenario

Host BHost A


ACK=100


Xtimeo

ut

ACK=100

premature timeout

Host BHost A


ACK=100


timeo

ut

ACK=120


ACK=120

SendBase=100

SendBase=120

SendBase=120

SendBase=92



X

cumulative ACK

Host BHost A


ACK=100


timeo

ut


ACK=120



event at receiver





TCP receiver action














TCP fast retransmit



X


Host BHost A


ACK=100

timeo

ut ACK=100

ACK=100ACK=100

TCP fast retransmit












control



process


TCPcode

IPcode

applicationOS





from sender


flow control


TCP flow control

buffered data


RcvBuffer


















control








application

network




application

network








2-way handshake

Letrsquos talk

OKESTAB

ESTAB


ESTABacc_conn(x)





ESTAB

req_conn(x)


client terminates

serverforgets x



ESTAB

req_conn(x)

data(x+1)

retransmitdata(x+1)

acceptdata(x+1)

choose xreq_conn(x)

ESTAB

ESTAB

acc_conn(x)

client terminates

ESTAB

choose xreq_conn(x)

ESTABacc_conn(x)



forgets x


TCP 3-way handshake

SYNbit=1 Seq=x


ESTAB



ACKbit=1 ACKnum=y+1




SYNSENT

ESTAB

SYN RCVD

client stateLISTEN

server stateLISTEN



closed

listen

SYNrcvd

SYNsent

ESTAB


SYN(seq=x)











FIN_WAIT_2

CLOSE_WAIT

FINbit=1 seq=y

ACKbit=1 ACKnum=y+1


close

can stillsend data


LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2max

segment lifetime

CLOSED



clientSocketclose()











control





a top-10 problem








Host A

original data in

Host B

throughput out

R2

R2

out

in R2de

lay








Host A

in original data

Host B


lsquo








free buffer space

R2

R2

out

in


Host B

A




no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







rsquo increase


Host A out


Host B

Host CHost D


retransmitted data







C2

C2

out

inrsquo










control





loss

cwnd

TCP

send

er

cong

estio

n w

indo

w s

ize


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwndRTT

bytessec






Host A

RTT

Host B

time



















cwnd gt ssthresh

congestionavoidance



new ACK


fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


WRTT bytessec










TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R






















linkphysical


linkphysical

ECN=00 ECN=11

ECE=1

IP datagram

TCP ACK segment






bull UDPbull TCP

next leaving the





X

cumulative ACK

Host BHost A


ACK=100


timeo

ut


ACK=120



event at receiver





TCP receiver action














TCP fast retransmit



X


Host BHost A


ACK=100

timeo

ut ACK=100

ACK=100ACK=100

TCP fast retransmit












control



process


TCPcode

IPcode

applicationOS





from sender


flow control


TCP flow control

buffered data


RcvBuffer


















control








application

network




application

network








2-way handshake

Letrsquos talk

OKESTAB

ESTAB


ESTABacc_conn(x)





ESTAB

req_conn(x)


client terminates

serverforgets x



ESTAB

req_conn(x)

data(x+1)

retransmitdata(x+1)

acceptdata(x+1)

choose xreq_conn(x)

ESTAB

ESTAB

acc_conn(x)

client terminates

ESTAB

choose xreq_conn(x)

ESTABacc_conn(x)



forgets x


TCP 3-way handshake

SYNbit=1 Seq=x


ESTAB



ACKbit=1 ACKnum=y+1




SYNSENT

ESTAB

SYN RCVD

client stateLISTEN

server stateLISTEN



closed

listen

SYNrcvd

SYNsent

ESTAB


SYN(seq=x)











FIN_WAIT_2

CLOSE_WAIT

FINbit=1 seq=y

ACKbit=1 ACKnum=y+1


close

can stillsend data


LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2max

segment lifetime

CLOSED



clientSocketclose()











control





a top-10 problem








Host A

original data in

Host B

throughput out

R2

R2

out

in R2de

lay








Host A

in original data

Host B


lsquo








free buffer space

R2

R2

out

in


Host B

A




no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







rsquo increase


Host A out


Host B

Host CHost D


retransmitted data







C2

C2

out

inrsquo










control





loss

cwnd

TCP

send

er

cong

estio

n w

indo

w s

ize


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwndRTT

bytessec






Host A

RTT

Host B

time



















cwnd gt ssthresh

congestionavoidance



new ACK


fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


WRTT bytessec










TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R






















linkphysical


linkphysical

ECN=00 ECN=11

ECE=1

IP datagram

TCP ACK segment






bull UDPbull TCP

next leaving the





event at receiver





TCP receiver action














TCP fast retransmit



X


Host BHost A


ACK=100

timeo

ut ACK=100

ACK=100ACK=100

TCP fast retransmit












control



process


TCPcode

IPcode

applicationOS





from sender


flow control


TCP flow control

buffered data


RcvBuffer


















control








application

network




application

network








2-way handshake

Letrsquos talk

OKESTAB

ESTAB


ESTABacc_conn(x)





ESTAB

req_conn(x)


client terminates

serverforgets x



ESTAB

req_conn(x)

data(x+1)

retransmitdata(x+1)

acceptdata(x+1)

choose xreq_conn(x)

ESTAB

ESTAB

acc_conn(x)

client terminates

ESTAB

choose xreq_conn(x)

ESTABacc_conn(x)



forgets x


TCP 3-way handshake

SYNbit=1 Seq=x


ESTAB



ACKbit=1 ACKnum=y+1




SYNSENT

ESTAB

SYN RCVD

client stateLISTEN

server stateLISTEN



closed

listen

SYNrcvd

SYNsent

ESTAB


SYN(seq=x)











FIN_WAIT_2

CLOSE_WAIT

FINbit=1 seq=y

ACKbit=1 ACKnum=y+1


close

can stillsend data


LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2max

segment lifetime

CLOSED



clientSocketclose()











control





a top-10 problem








Host A

original data in

Host B

throughput out

R2

R2

out

in R2de

lay








Host A

in original data

Host B


lsquo








free buffer space

R2

R2

out

in


Host B

A




no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







rsquo increase


Host A out


Host B

Host CHost D


retransmitted data







C2

C2

out

inrsquo










control





loss

cwnd

TCP

send

er

cong

estio

n w

indo

w s

ize


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwndRTT

bytessec






Host A

RTT

Host B

time



















cwnd gt ssthresh

congestionavoidance



new ACK


fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


WRTT bytessec










TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R






















linkphysical


linkphysical

ECN=00 ECN=11

ECE=1

IP datagram

TCP ACK segment






bull UDPbull TCP

next leaving the












TCP fast retransmit



X


Host BHost A


ACK=100

timeo

ut ACK=100

ACK=100ACK=100

TCP fast retransmit












control



process


TCPcode

IPcode

applicationOS





from sender


flow control


TCP flow control

buffered data


RcvBuffer


















control








application

network




application

network








2-way handshake

Letrsquos talk

OKESTAB

ESTAB


ESTABacc_conn(x)





ESTAB

req_conn(x)


client terminates

serverforgets x



ESTAB

req_conn(x)

data(x+1)

retransmitdata(x+1)

acceptdata(x+1)

choose xreq_conn(x)

ESTAB

ESTAB

acc_conn(x)

client terminates

ESTAB

choose xreq_conn(x)

ESTABacc_conn(x)



forgets x


TCP 3-way handshake

SYNbit=1 Seq=x


ESTAB



ACKbit=1 ACKnum=y+1




SYNSENT

ESTAB

SYN RCVD

client stateLISTEN

server stateLISTEN



closed

listen

SYNrcvd

SYNsent

ESTAB


SYN(seq=x)











FIN_WAIT_2

CLOSE_WAIT

FINbit=1 seq=y

ACKbit=1 ACKnum=y+1


close

can stillsend data


LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2max

segment lifetime

CLOSED



clientSocketclose()











control





a top-10 problem








Host A

original data in

Host B

throughput out

R2

R2

out

in R2de

lay








Host A

in original data

Host B


lsquo








free buffer space

R2

R2

out

in


Host B

A




no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







rsquo increase


Host A out


Host B

Host CHost D


retransmitted data







C2

C2

out

inrsquo










control





loss

cwnd

TCP

send

er

cong

estio

n w

indo

w s

ize


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwndRTT

bytessec






Host A

RTT

Host B

time



















cwnd gt ssthresh

congestionavoidance



new ACK


fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


WRTT bytessec










TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R






















linkphysical


linkphysical

ECN=00 ECN=11

ECE=1

IP datagram

TCP ACK segment






bull UDPbull TCP

next leaving the




X


Host BHost A


ACK=100

timeo

ut ACK=100

ACK=100ACK=100

TCP fast retransmit












control



process


TCPcode

IPcode

applicationOS





from sender


flow control


TCP flow control

buffered data


RcvBuffer


















control








application

network




application

network








2-way handshake

Letrsquos talk

OKESTAB

ESTAB


ESTABacc_conn(x)





ESTAB

req_conn(x)


client terminates

serverforgets x



ESTAB

req_conn(x)

data(x+1)

retransmitdata(x+1)

acceptdata(x+1)

choose xreq_conn(x)

ESTAB

ESTAB

acc_conn(x)

client terminates

ESTAB

choose xreq_conn(x)

ESTABacc_conn(x)



forgets x


TCP 3-way handshake

SYNbit=1 Seq=x


ESTAB



ACKbit=1 ACKnum=y+1




SYNSENT

ESTAB

SYN RCVD

client stateLISTEN

server stateLISTEN



closed

listen

SYNrcvd

SYNsent

ESTAB


SYN(seq=x)











FIN_WAIT_2

CLOSE_WAIT

FINbit=1 seq=y

ACKbit=1 ACKnum=y+1


close

can stillsend data


LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2max

segment lifetime

CLOSED



clientSocketclose()











control





a top-10 problem








Host A

original data in

Host B

throughput out

R2

R2

out

in R2de

lay








Host A

in original data

Host B


lsquo








free buffer space

R2

R2

out

in


Host B

A




no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







rsquo increase


Host A out


Host B

Host CHost D


retransmitted data







C2

C2

out

inrsquo










control





loss

cwnd

TCP

send

er

cong

estio

n w

indo

w s

ize


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwndRTT

bytessec






Host A

RTT

Host B

time



















cwnd gt ssthresh

congestionavoidance



new ACK


fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


WRTT bytessec










TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R






















linkphysical


linkphysical

ECN=00 ECN=11

ECE=1

IP datagram

TCP ACK segment






bull UDPbull TCP

next leaving the












control



process


TCPcode

IPcode

applicationOS





from sender


flow control


TCP flow control

buffered data


RcvBuffer


















control








application

network




application

network








2-way handshake

Letrsquos talk

OKESTAB

ESTAB


ESTABacc_conn(x)





ESTAB

req_conn(x)


client terminates

serverforgets x



ESTAB

req_conn(x)

data(x+1)

retransmitdata(x+1)

acceptdata(x+1)

choose xreq_conn(x)

ESTAB

ESTAB

acc_conn(x)

client terminates

ESTAB

choose xreq_conn(x)

ESTABacc_conn(x)



forgets x


TCP 3-way handshake

SYNbit=1 Seq=x


ESTAB



ACKbit=1 ACKnum=y+1




SYNSENT

ESTAB

SYN RCVD

client stateLISTEN

server stateLISTEN



closed

listen

SYNrcvd

SYNsent

ESTAB


SYN(seq=x)











FIN_WAIT_2

CLOSE_WAIT

FINbit=1 seq=y

ACKbit=1 ACKnum=y+1


close

can stillsend data


LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2max

segment lifetime

CLOSED



clientSocketclose()











control





a top-10 problem








Host A

original data in

Host B

throughput out

R2

R2

out

in R2de

lay








Host A

in original data

Host B


lsquo








free buffer space

R2

R2

out

in


Host B

A




no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







rsquo increase


Host A out


Host B

Host CHost D


retransmitted data







C2

C2

out

inrsquo










control





loss

cwnd

TCP

send

er

cong

estio

n w

indo

w s

ize


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwndRTT

bytessec






Host A

RTT

Host B

time



















cwnd gt ssthresh

congestionavoidance



new ACK


fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


WRTT bytessec










TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R






















linkphysical


linkphysical

ECN=00 ECN=11

ECE=1

IP datagram

TCP ACK segment






bull UDPbull TCP

next leaving the





process


TCPcode

IPcode

applicationOS





from sender


flow control


TCP flow control

buffered data


RcvBuffer


















control








application

network




application

network








2-way handshake

Letrsquos talk

OKESTAB

ESTAB


ESTABacc_conn(x)





ESTAB

req_conn(x)


client terminates

serverforgets x



ESTAB

req_conn(x)

data(x+1)

retransmitdata(x+1)

acceptdata(x+1)

choose xreq_conn(x)

ESTAB

ESTAB

acc_conn(x)

client terminates

ESTAB

choose xreq_conn(x)

ESTABacc_conn(x)



forgets x


TCP 3-way handshake

SYNbit=1 Seq=x


ESTAB



ACKbit=1 ACKnum=y+1




SYNSENT

ESTAB

SYN RCVD

client stateLISTEN

server stateLISTEN



closed

listen

SYNrcvd

SYNsent

ESTAB


SYN(seq=x)











FIN_WAIT_2

CLOSE_WAIT

FINbit=1 seq=y

ACKbit=1 ACKnum=y+1


close

can stillsend data


LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2max

segment lifetime

CLOSED



clientSocketclose()











control





a top-10 problem








Host A

original data in

Host B

throughput out

R2

R2

out

in R2de

lay








Host A

in original data

Host B


lsquo








free buffer space

R2

R2

out

in


Host B

A




no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







rsquo increase


Host A out


Host B

Host CHost D


retransmitted data







C2

C2

out

inrsquo










control





loss

cwnd

TCP

send

er

cong

estio

n w

indo

w s

ize


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwndRTT

bytessec






Host A

RTT

Host B

time



















cwnd gt ssthresh

congestionavoidance



new ACK


fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


WRTT bytessec










TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R






















linkphysical


linkphysical

ECN=00 ECN=11

ECE=1

IP datagram

TCP ACK segment






bull UDPbull TCP

next leaving the




TCP flow control

buffered data


RcvBuffer


















control








application

network




application

network








2-way handshake

Letrsquos talk

OKESTAB

ESTAB


ESTABacc_conn(x)





ESTAB

req_conn(x)


client terminates

serverforgets x



ESTAB

req_conn(x)

data(x+1)

retransmitdata(x+1)

acceptdata(x+1)

choose xreq_conn(x)

ESTAB

ESTAB

acc_conn(x)

client terminates

ESTAB

choose xreq_conn(x)

ESTABacc_conn(x)



forgets x


TCP 3-way handshake

SYNbit=1 Seq=x


ESTAB



ACKbit=1 ACKnum=y+1




SYNSENT

ESTAB

SYN RCVD

client stateLISTEN

server stateLISTEN



closed

listen

SYNrcvd

SYNsent

ESTAB


SYN(seq=x)











FIN_WAIT_2

CLOSE_WAIT

FINbit=1 seq=y

ACKbit=1 ACKnum=y+1


close

can stillsend data


LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2max

segment lifetime

CLOSED



clientSocketclose()











control





a top-10 problem








Host A

original data in

Host B

throughput out

R2

R2

out

in R2de

lay








Host A

in original data

Host B


lsquo








free buffer space

R2

R2

out

in


Host B

A




no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







rsquo increase


Host A out


Host B

Host CHost D


retransmitted data







C2

C2

out

inrsquo










control





loss

cwnd

TCP

send

er

cong

estio

n w

indo

w s

ize


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwndRTT

bytessec






Host A

RTT

Host B

time



















cwnd gt ssthresh

congestionavoidance



new ACK


fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


WRTT bytessec










TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R






















linkphysical


linkphysical

ECN=00 ECN=11

ECE=1

IP datagram

TCP ACK segment






bull UDPbull TCP

next leaving the












control








application

network




application

network








2-way handshake

Letrsquos talk

OKESTAB

ESTAB


ESTABacc_conn(x)





ESTAB

req_conn(x)


client terminates

serverforgets x



ESTAB

req_conn(x)

data(x+1)

retransmitdata(x+1)

acceptdata(x+1)

choose xreq_conn(x)

ESTAB

ESTAB

acc_conn(x)

client terminates

ESTAB

choose xreq_conn(x)

ESTABacc_conn(x)



forgets x


TCP 3-way handshake

SYNbit=1 Seq=x


ESTAB



ACKbit=1 ACKnum=y+1




SYNSENT

ESTAB

SYN RCVD

client stateLISTEN

server stateLISTEN



closed

listen

SYNrcvd

SYNsent

ESTAB


SYN(seq=x)











FIN_WAIT_2

CLOSE_WAIT

FINbit=1 seq=y

ACKbit=1 ACKnum=y+1


close

can stillsend data


LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2max

segment lifetime

CLOSED



clientSocketclose()











control





a top-10 problem








Host A

original data in

Host B

throughput out

R2

R2

out

in R2de

lay








Host A

in original data

Host B


lsquo








free buffer space

R2

R2

out

in


Host B

A




no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







rsquo increase


Host A out


Host B

Host CHost D


retransmitted data







C2

C2

out

inrsquo










control





loss

cwnd

TCP

send

er

cong

estio

n w

indo

w s

ize


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwndRTT

bytessec






Host A

RTT

Host B

time



















cwnd gt ssthresh

congestionavoidance



new ACK


fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


WRTT bytessec










TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R






















linkphysical


linkphysical

ECN=00 ECN=11

ECE=1

IP datagram

TCP ACK segment






bull UDPbull TCP

next leaving the










application

network




application

network








2-way handshake

Letrsquos talk

OKESTAB

ESTAB


ESTABacc_conn(x)





ESTAB

req_conn(x)


client terminates

serverforgets x



ESTAB

req_conn(x)

data(x+1)

retransmitdata(x+1)

acceptdata(x+1)

choose xreq_conn(x)

ESTAB

ESTAB

acc_conn(x)

client terminates

ESTAB

choose xreq_conn(x)

ESTABacc_conn(x)



forgets x


TCP 3-way handshake

SYNbit=1 Seq=x


ESTAB



ACKbit=1 ACKnum=y+1




SYNSENT

ESTAB

SYN RCVD

client stateLISTEN

server stateLISTEN



closed

listen

SYNrcvd

SYNsent

ESTAB


SYN(seq=x)











FIN_WAIT_2

CLOSE_WAIT

FINbit=1 seq=y

ACKbit=1 ACKnum=y+1


close

can stillsend data


LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2max

segment lifetime

CLOSED



clientSocketclose()











control





a top-10 problem








Host A

original data in

Host B

throughput out

R2

R2

out

in R2de

lay








Host A

in original data

Host B


lsquo








free buffer space

R2

R2

out

in


Host B

A




no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







rsquo increase


Host A out


Host B

Host CHost D


retransmitted data







C2

C2

out

inrsquo










control





loss

cwnd

TCP

send

er

cong

estio

n w

indo

w s

ize


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwndRTT

bytessec






Host A

RTT

Host B

time



















cwnd gt ssthresh

congestionavoidance



new ACK


fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


WRTT bytessec










TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R






















linkphysical


linkphysical

ECN=00 ECN=11

ECE=1

IP datagram

TCP ACK segment






bull UDPbull TCP

next leaving the








2-way handshake

Letrsquos talk

OKESTAB

ESTAB


ESTABacc_conn(x)





ESTAB

req_conn(x)


client terminates

serverforgets x



ESTAB

req_conn(x)

data(x+1)

retransmitdata(x+1)

acceptdata(x+1)

choose xreq_conn(x)

ESTAB

ESTAB

acc_conn(x)

client terminates

ESTAB

choose xreq_conn(x)

ESTABacc_conn(x)



forgets x


TCP 3-way handshake

SYNbit=1 Seq=x


ESTAB



ACKbit=1 ACKnum=y+1




SYNSENT

ESTAB

SYN RCVD

client stateLISTEN

server stateLISTEN



closed

listen

SYNrcvd

SYNsent

ESTAB


SYN(seq=x)











FIN_WAIT_2

CLOSE_WAIT

FINbit=1 seq=y

ACKbit=1 ACKnum=y+1


close

can stillsend data


LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2max

segment lifetime

CLOSED



clientSocketclose()











control





a top-10 problem








Host A

original data in

Host B

throughput out

R2

R2

out

in R2de

lay








Host A

in original data

Host B


lsquo








free buffer space

R2

R2

out

in


Host B

A




no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







rsquo increase


Host A out


Host B

Host CHost D


retransmitted data







C2

C2

out

inrsquo










control





loss

cwnd

TCP

send

er

cong

estio

n w

indo

w s

ize


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwndRTT

bytessec






Host A

RTT

Host B

time



















cwnd gt ssthresh

congestionavoidance



new ACK


fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


WRTT bytessec










TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R






















linkphysical


linkphysical

ECN=00 ECN=11

ECE=1

IP datagram

TCP ACK segment






bull UDPbull TCP

next leaving the






ESTAB

req_conn(x)


client terminates

serverforgets x



ESTAB

req_conn(x)

data(x+1)

retransmitdata(x+1)

acceptdata(x+1)

choose xreq_conn(x)

ESTAB

ESTAB

acc_conn(x)

client terminates

ESTAB

choose xreq_conn(x)

ESTABacc_conn(x)



forgets x


TCP 3-way handshake

SYNbit=1 Seq=x


ESTAB



ACKbit=1 ACKnum=y+1




SYNSENT

ESTAB

SYN RCVD

client stateLISTEN

server stateLISTEN



closed

listen

SYNrcvd

SYNsent

ESTAB


SYN(seq=x)











FIN_WAIT_2

CLOSE_WAIT

FINbit=1 seq=y

ACKbit=1 ACKnum=y+1


close

can stillsend data


LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2max

segment lifetime

CLOSED



clientSocketclose()











control





a top-10 problem








Host A

original data in

Host B

throughput out

R2

R2

out

in R2de

lay








Host A

in original data

Host B


lsquo








free buffer space

R2

R2

out

in


Host B

A




no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







rsquo increase


Host A out


Host B

Host CHost D


retransmitted data







C2

C2

out

inrsquo










control





loss

cwnd

TCP

send

er

cong

estio

n w

indo

w s

ize


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwndRTT

bytessec






Host A

RTT

Host B

time



















cwnd gt ssthresh

congestionavoidance



new ACK


fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


WRTT bytessec










TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R






















linkphysical


linkphysical

ECN=00 ECN=11

ECE=1

IP datagram

TCP ACK segment






bull UDPbull TCP

next leaving the




TCP 3-way handshake

SYNbit=1 Seq=x


ESTAB



ACKbit=1 ACKnum=y+1




SYNSENT

ESTAB

SYN RCVD

client stateLISTEN

server stateLISTEN



closed

listen

SYNrcvd

SYNsent

ESTAB


SYN(seq=x)











FIN_WAIT_2

CLOSE_WAIT

FINbit=1 seq=y

ACKbit=1 ACKnum=y+1


close

can stillsend data


LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2max

segment lifetime

CLOSED



clientSocketclose()











control





a top-10 problem








Host A

original data in

Host B

throughput out

R2

R2

out

in R2de

lay








Host A

in original data

Host B


lsquo








free buffer space

R2

R2

out

in


Host B

A




no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







rsquo increase


Host A out


Host B

Host CHost D


retransmitted data







C2

C2

out

inrsquo










control





loss

cwnd

TCP

send

er

cong

estio

n w

indo

w s

ize


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwndRTT

bytessec






Host A

RTT

Host B

time



















cwnd gt ssthresh

congestionavoidance



new ACK


fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


WRTT bytessec










TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R






















linkphysical


linkphysical

ECN=00 ECN=11

ECE=1

IP datagram

TCP ACK segment






bull UDPbull TCP

next leaving the





closed

listen

SYNrcvd

SYNsent

ESTAB


SYN(seq=x)











FIN_WAIT_2

CLOSE_WAIT

FINbit=1 seq=y

ACKbit=1 ACKnum=y+1


close

can stillsend data


LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2max

segment lifetime

CLOSED



clientSocketclose()











control





a top-10 problem








Host A

original data in

Host B

throughput out

R2

R2

out

in R2de

lay








Host A

in original data

Host B


lsquo








free buffer space

R2

R2

out

in


Host B

A




no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







rsquo increase


Host A out


Host B

Host CHost D


retransmitted data







C2

C2

out

inrsquo










control





loss

cwnd

TCP

send

er

cong

estio

n w

indo

w s

ize


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwndRTT

bytessec






Host A

RTT

Host B

time



















cwnd gt ssthresh

congestionavoidance



new ACK


fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


WRTT bytessec










TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R






















linkphysical


linkphysical

ECN=00 ECN=11

ECE=1

IP datagram

TCP ACK segment






bull UDPbull TCP

next leaving the









FIN_WAIT_2

CLOSE_WAIT

FINbit=1 seq=y

ACKbit=1 ACKnum=y+1


close

can stillsend data


LAST_ACK

CLOSED

TIMED_WAIT

timed wait for 2max

segment lifetime

CLOSED



clientSocketclose()











control





a top-10 problem








Host A

original data in

Host B

throughput out

R2

R2

out

in R2de

lay








Host A

in original data

Host B


lsquo








free buffer space

R2

R2

out

in


Host B

A




no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







rsquo increase


Host A out


Host B

Host CHost D


retransmitted data







C2

C2

out

inrsquo










control





loss

cwnd

TCP

send

er

cong

estio

n w

indo

w s

ize


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwndRTT

bytessec






Host A

RTT

Host B

time



















cwnd gt ssthresh

congestionavoidance



new ACK


fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


WRTT bytessec










TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R






















linkphysical


linkphysical

ECN=00 ECN=11

ECE=1

IP datagram

TCP ACK segment






bull UDPbull TCP

next leaving the












control





a top-10 problem








Host A

original data in

Host B

throughput out

R2

R2

out

in R2de

lay








Host A

in original data

Host B


lsquo








free buffer space

R2

R2

out

in


Host B

A




no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







rsquo increase


Host A out


Host B

Host CHost D


retransmitted data







C2

C2

out

inrsquo










control





loss

cwnd

TCP

send

er

cong

estio

n w

indo

w s

ize


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwndRTT

bytessec






Host A

RTT

Host B

time



















cwnd gt ssthresh

congestionavoidance



new ACK


fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


WRTT bytessec










TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R






















linkphysical


linkphysical

ECN=00 ECN=11

ECE=1

IP datagram

TCP ACK segment






bull UDPbull TCP

next leaving the







a top-10 problem








Host A

original data in

Host B

throughput out

R2

R2

out

in R2de

lay








Host A

in original data

Host B


lsquo








free buffer space

R2

R2

out

in


Host B

A




no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







rsquo increase


Host A out


Host B

Host CHost D


retransmitted data







C2

C2

out

inrsquo










control





loss

cwnd

TCP

send

er

cong

estio

n w

indo

w s

ize


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwndRTT

bytessec






Host A

RTT

Host B

time



















cwnd gt ssthresh

congestionavoidance



new ACK


fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


WRTT bytessec










TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R






















linkphysical


linkphysical

ECN=00 ECN=11

ECE=1

IP datagram

TCP ACK segment






bull UDPbull TCP

next leaving the









Host A

original data in

Host B

throughput out

R2

R2

out

in R2de

lay








Host A

in original data

Host B


lsquo








free buffer space

R2

R2

out

in


Host B

A




no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







rsquo increase


Host A out


Host B

Host CHost D


retransmitted data







C2

C2

out

inrsquo










control





loss

cwnd

TCP

send

er

cong

estio

n w

indo

w s

ize


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwndRTT

bytessec






Host A

RTT

Host B

time



















cwnd gt ssthresh

congestionavoidance



new ACK


fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


WRTT bytessec










TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R






















linkphysical


linkphysical

ECN=00 ECN=11

ECE=1

IP datagram

TCP ACK segment






bull UDPbull TCP

next leaving the








Host A

in original data

Host B


lsquo








free buffer space

R2

R2

out

in


Host B

A




no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







rsquo increase


Host A out


Host B

Host CHost D


retransmitted data







C2

C2

out

inrsquo










control





loss

cwnd

TCP

send

er

cong

estio

n w

indo

w s

ize


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwndRTT

bytessec






Host A

RTT

Host B

time



















cwnd gt ssthresh

congestionavoidance



new ACK


fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


WRTT bytessec










TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R






















linkphysical


linkphysical

ECN=00 ECN=11

ECE=1

IP datagram

TCP ACK segment






bull UDPbull TCP

next leaving the









free buffer space

R2

R2

out

in


Host B

A




no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







rsquo increase


Host A out


Host B

Host CHost D


retransmitted data







C2

C2

out

inrsquo










control





loss

cwnd

TCP

send

er

cong

estio

n w

indo

w s

ize


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwndRTT

bytessec






Host A

RTT

Host B

time



















cwnd gt ssthresh

congestionavoidance



new ACK


fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


WRTT bytessec










TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R






















linkphysical


linkphysical

ECN=00 ECN=11

ECE=1

IP datagram

TCP ACK segment






bull UDPbull TCP

next leaving the






no buffer space




A

Host B



retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







rsquo increase


Host A out


Host B

Host CHost D


retransmitted data







C2

C2

out

inrsquo










control





loss

cwnd

TCP

send

er

cong

estio

n w

indo

w s

ize


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwndRTT

bytessec






Host A

RTT

Host B

time



















cwnd gt ssthresh

congestionavoidance



new ACK


fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


WRTT bytessec










TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R






















linkphysical


linkphysical

ECN=00 ECN=11

ECE=1

IP datagram

TCP ACK segment






bull UDPbull TCP

next leaving the





retransmitted data

free buffer space




R2

R2in

out


A

Host B


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







rsquo increase


Host A out


Host B

Host CHost D


retransmitted data







C2

C2

out

inrsquo










control





loss

cwnd

TCP

send

er

cong

estio

n w

indo

w s

ize


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwndRTT

bytessec






Host A

RTT

Host B

time



















cwnd gt ssthresh

congestionavoidance



new ACK


fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


WRTT bytessec










TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R






















linkphysical


linkphysical

ECN=00 ECN=11

ECE=1

IP datagram

TCP ACK segment






bull UDPbull TCP

next leaving the




A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out




R2in







rsquo increase


Host A out


Host B

Host CHost D


retransmitted data







C2

C2

out

inrsquo










control





loss

cwnd

TCP

send

er

cong

estio

n w

indo

w s

ize


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwndRTT

bytessec






Host A

RTT

Host B

time



















cwnd gt ssthresh

congestionavoidance



new ACK


fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


WRTT bytessec










TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R






















linkphysical


linkphysical

ECN=00 ECN=11

ECE=1

IP datagram

TCP ACK segment






bull UDPbull TCP

next leaving the




R2

out




R2in







rsquo increase


Host A out


Host B

Host CHost D


retransmitted data







C2

C2

out

inrsquo










control





loss

cwnd

TCP

send

er

cong

estio

n w

indo

w s

ize


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwndRTT

bytessec






Host A

RTT

Host B

time



















cwnd gt ssthresh

congestionavoidance



new ACK


fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


WRTT bytessec










TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R






















linkphysical


linkphysical

ECN=00 ECN=11

ECE=1

IP datagram

TCP ACK segment






bull UDPbull TCP

next leaving the






rsquo increase


Host A out


Host B

Host CHost D


retransmitted data







C2

C2

out

inrsquo










control





loss

cwnd

TCP

send

er

cong

estio

n w

indo

w s

ize


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwndRTT

bytessec






Host A

RTT

Host B

time



















cwnd gt ssthresh

congestionavoidance



new ACK


fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


WRTT bytessec










TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R






















linkphysical


linkphysical

ECN=00 ECN=11

ECE=1

IP datagram

TCP ACK segment






bull UDPbull TCP

next leaving the







C2

C2

out

inrsquo










control





loss

cwnd

TCP

send

er

cong

estio

n w

indo

w s

ize


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwndRTT

bytessec






Host A

RTT

Host B

time



















cwnd gt ssthresh

congestionavoidance



new ACK


fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


WRTT bytessec










TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R






















linkphysical


linkphysical

ECN=00 ECN=11

ECE=1

IP datagram

TCP ACK segment






bull UDPbull TCP

next leaving the












control





loss

cwnd

TCP

send

er

cong

estio

n w

indo

w s

ize


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwndRTT

bytessec






Host A

RTT

Host B

time



















cwnd gt ssthresh

congestionavoidance



new ACK


fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


WRTT bytessec










TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R






















linkphysical


linkphysical

ECN=00 ECN=11

ECE=1

IP datagram

TCP ACK segment






bull UDPbull TCP

next leaving the







loss

cwnd

TCP

send

er

cong

estio

n w

indo

w s

ize


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate ~~cwndRTT

bytessec






Host A

RTT

Host B

time



















cwnd gt ssthresh

congestionavoidance



new ACK


fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


WRTT bytessec










TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R






















linkphysical


linkphysical

ECN=00 ECN=11

ECE=1

IP datagram

TCP ACK segment






bull UDPbull TCP

next leaving the











last byte sent

cwnd


lt cwnd


rate ~~cwndRTT

bytessec






Host A

RTT

Host B

time



















cwnd gt ssthresh

congestionavoidance



new ACK


fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


WRTT bytessec










TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R






















linkphysical


linkphysical

ECN=00 ECN=11

ECE=1

IP datagram

TCP ACK segment






bull UDPbull TCP

next leaving the








Host A

RTT

Host B

time



















cwnd gt ssthresh

congestionavoidance



new ACK


fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


WRTT bytessec










TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R






















linkphysical


linkphysical

ECN=00 ECN=11

ECE=1

IP datagram

TCP ACK segment






bull UDPbull TCP

next leaving the





















cwnd gt ssthresh

congestionavoidance



new ACK


fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start






cwnd = 1 MSS


NewACK

NewACK

NewACK





W

W2


WRTT bytessec










TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R






















linkphysical


linkphysical

ECN=00 ECN=11

ECE=1

IP datagram

TCP ACK segment






bull UDPbull TCP

next leaving the







W

W2


WRTT bytessec










TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R






















linkphysical


linkphysical

ECN=00 ECN=11

ECE=1

IP datagram

TCP ACK segment






bull UDPbull TCP

next leaving the












TCP connection 1

bottleneckrouter

capacity R

TCP Fairness

TCP connection 2




proportionally R

R






















linkphysical


linkphysical

ECN=00 ECN=11

ECE=1

IP datagram

TCP ACK segment






bull UDPbull TCP

next leaving the






proportionally R

R






















linkphysical


linkphysical

ECN=00 ECN=11

ECE=1

IP datagram

TCP ACK segment






bull UDPbull TCP

next leaving the




















linkphysical


linkphysical

ECN=00 ECN=11

ECE=1

IP datagram

TCP ACK segment






bull UDPbull TCP

next leaving the








bull UDPbull TCP

next leaving the



chapter 3 transport layer - university of...

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