1 john magee 20 february 2014 cs 280: transport layer: congestion control concepts, tcp congestion...

1

John Magee20 February 2014

CS 280Transport Layer

Congestion Control ConceptsTCP Congestion Control

Most slides adapted from Kurose and Ross Computer Networking 6e Source material copyright 1996-2012

JF Kurose and KW Ross

Transport Layer 3-2

Chapter 3 Transport Layerour goals understand

principles behind transport layer services multiplexing

demultiplexing reliable data

transfer flow control congestion

control

learn about Internet transport layer protocols UDP connectionless

transport TCP connection-

oriented reliable transport

TCP congestion control

Transport Layer 3-3

Chapter 3 outline

31 transport-layer services

32 multiplexing and demultiplexing

33 connectionless transport UDP

34 principles of reliable data transfer

35 connection-oriented transport TCP segment structure reliable data transfer flow control connection

management36 principles of

congestion control37 TCP congestion

control

Transport Layer 3-4

congestion informally ldquotoo many sources sending

too much data too fast for network to handlerdquo

different from flow control manifestations

lost packets (buffer overflow at routers)

long delays (queueing in router buffers)

a top-10 problem

Principles of congestion control

Transport Layer 3-5

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

throughputout

R2

R2

out

in R2d

ela

yin

large delays as arrival rate in approaches capacity

Transport Layer 3-6

one router finite buffers sender retransmission of timed-out packet

application-layer input = application-layer outputin

= out

transport-layer input includes retransmissions in in

finite shared output link buffers

Host A

in original data

Host B

outin original data plus

retransmitted data

lsquo


Transport Layer 3-7

idealization perfect knowledge

sender sends only when router buffers available


in original dataoutin original data plus

retransmitted data

copy

free buffer space

R2

R2

out

in


Host B

A

Transport Layer 3-8


retransmitted data

copy

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

Transport Layer 3-9


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

Transport Layer 3-10

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 two copies both of which are delivered



R2

out


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

decreasing goodput

R2in

Causescosts of congestion scenario 2 Realistic 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 C

Host D

in original data

in 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

ou

t

inrsquo


Approaches towards congestion controltwo broad approaches towards congestion

controlend-end

congestion control

no explicit feedback from network

congestion inferred from end-system observed loss delay

approach taken by TCP

network-assisted congestion control

routers provide feedback to end systemssingle bit indicating congestion (SNA DECbit TCPIP ECN ATM)

explicit rate for sender to send at


Case study ATM ABR congestion control

ABR available bit rate

ldquoelastic servicerdquo if senderrsquos path

ldquounderloadedrdquo sender should

use available bandwidth

if senderrsquos path congested sender throttled

to minimum guaranteed rate

RM (resource management) cells

sent by sender interspersed with data cells

bits in RM cell set by switches (ldquonetwork-assistedrdquo) NI bit no increase in rate

(mild congestion) CI bit congestion

indication RM cells returned to sender

by receiver with bits intact



two-byte ER (explicit rate) field in RM cell congested switch may lower ER value in cell sendersrsquo send rate thus max supportable rate on path

EFCI bit in data cells set to 1 in congested switch if data cell preceding RM cell has EFCI set receiver

sets CI bit in returned RM cell

RM cell data cell


Chapter 3 outline








control


TCP congestion control additive increase multiplicative decrease

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

MSS every RTT until loss detected multiplicative decrease cut cwnd in half

after loss

cwnd

TC

P s

ende

r co

nges

tion

win

dow

siz

e

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

sender sequence number space

rate~~cwnd

RTTbytessec


TCP Slow Start when connection

begins increase rate exponentially until first loss event initially cwnd = 1 MSS double cwnd every

RTT done by incrementing cwnd for every ACK received

summary initial rate is slow but ramps up exponentially fast

Host A

one segment

RT

T

Host B

time

two segments

four segments


TCP detecting reacting to loss

loss indicated by timeout cwnd set to 1 MSS window then grows exponentially (as in slow start) to threshold

then grows linearly loss indicated by 3 duplicate ACKs TCP RENO

dup ACKs indicate network capable of delivering some segments 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 = cwnd2cwnd = 1 MSSdupACKcount = 0retransmit missing segment

cwnd gt ssthresh

congestionavoidance

cwnd = cwnd + MSS (MSScwnd)dupACKcount = 0transmit 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

retransmit missing segment

dupACKcount == 3

timeoutssthresh = cwnd2cwnd = 1 dupACKcount = 0retransmit missing segment

ssthresh= cwnd2cwnd = ssthresh + 3retransmit missing segment

dupACKcount == 3cwnd = ssthreshdupACKcount = 0

New ACK

slow start

timeoutssthresh = cwnd2 cwnd = 1 MSSdupACKcount = 0retransmit missing segment

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

new ACKdupACKcount++

duplicate ACK

cwnd = 1 MSSssthresh = 64 KBdupACKcount = 0

NewACK

NewACK

NewACK


TCP throughput avg TCP thruput as function of window

size RTT ignore slow start assume always data to send

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

W

W2

avg TCP thruput = 34W

RTTbytessec


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

bottleneckroutercapacity 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

Con

nect

ion

2 th

roug

h pu t

congestion avoidance additive increaseloss decrease window by factor of 2



Fairness (more)Fairness and UDP multimedia apps

often do not use TCP do not want rate

throttled by congestion control

instead use UDP 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 new app asks for 1 TCP gets

rate R10 new app asks for 11 TCPs gets

R2


Chapter 3 summary principles behind transport

layer services multiplexing

demultiplexing reliable data transfer flow control congestion control

instantiation implementation in the Internet UDP TCP

next leaving the

network ldquoedgerdquo (application transport layers)

into the network ldquocorerdquo

John Magee 20 February 2014

Chapter 3 Transport Layer

Chapter 3 outline




Slide 7

Slide 8

Slide 9

Slide 10

Slide 11


Slide 13

Approaches towards congestion control


Slide 16

Slide 17



TCP Slow Start




TCP throughput

TCP Futures TCP over ldquolong fat pipesrdquo

TCP Fairness

Why is TCP fair

Fairness (more)

Chapter 3 summary

Transport Layer 3-2

Chapter 3 Transport Layerour goals understand

principles behind transport layer services multiplexing

demultiplexing reliable data

transfer flow control congestion

control

learn about Internet transport layer protocols UDP connectionless

transport TCP connection-

oriented reliable transport

TCP congestion control

Transport Layer 3-3

Chapter 3 outline








control

Transport Layer 3-4






a top-10 problem


Transport Layer 3-5





no retransmission



Host A

original data in

Host B

throughputout

R2

R2

out

in R2d

ela

yin


Transport Layer 3-6



= out



Host A

in original data

Host B


retransmitted data

lsquo


Transport Layer 3-7





retransmitted data

copy

free buffer space

R2

R2

out

in


Host B

A

Transport Layer 3-8


retransmitted data

copy

no buffer space




A

Host B

Transport Layer 3-9


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



decreasing goodput

R2in







rsquo increase


Host A out


Host B

Host C

Host D

in original data


retransmitted data







C2

C2

ou

t

inrsquo



controlend-end

congestion control


























RM cell data cell


Chapter 3 outline








control





after loss

cwnd

TC

P s

ende

r co

nges

tion

win

dow

siz

e


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate~~cwnd

RTTbytessec






Host A

one segment

RT

T

Host B

time

two segments

four segments















cwnd gt ssthresh

congestionavoidance


new ACK

dupACKcount++

duplicate ACK

fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start




duplicate ACK


NewACK

NewACK

NewACK





W

W2


RTTbytessec










TCP connection 1


TCP Fairness

TCP connection 2




proportionally R

R



Con

nect

ion

2 th

roug

h pu t














R2






next leaving the





Chapter 3 outline




Slide 7

Slide 8

Slide 9

Slide 10

Slide 11


Slide 13



Slide 16

Slide 17



TCP Slow Start




TCP throughput


TCP Fairness

Why is TCP fair

Fairness (more)

Chapter 3 summary

Transport Layer 3-3

Chapter 3 outline








control

Transport Layer 3-4






a top-10 problem


Transport Layer 3-5





no retransmission



Host A

original data in

Host B

throughputout

R2

R2

out

in R2d

ela

yin


Transport Layer 3-6



= out



Host A

in original data

Host B


retransmitted data

lsquo


Transport Layer 3-7





retransmitted data

copy

free buffer space

R2

R2

out

in


Host B

A

Transport Layer 3-8


retransmitted data

copy

no buffer space




A

Host B

Transport Layer 3-9


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



decreasing goodput

R2in







rsquo increase


Host A out


Host B

Host C

Host D

in original data


retransmitted data







C2

C2

ou

t

inrsquo



controlend-end

congestion control


























RM cell data cell


Chapter 3 outline








control





after loss

cwnd

TC

P s

ende

r co

nges

tion

win

dow

siz

e


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate~~cwnd

RTTbytessec






Host A

one segment

RT

T

Host B

time

two segments

four segments















cwnd gt ssthresh

congestionavoidance


new ACK

dupACKcount++

duplicate ACK

fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start




duplicate ACK


NewACK

NewACK

NewACK





W

W2


RTTbytessec










TCP connection 1


TCP Fairness

TCP connection 2




proportionally R

R



Con

nect

ion

2 th

roug

h pu t














R2






next leaving the





Chapter 3 outline




Slide 7

Slide 8

Slide 9

Slide 10

Slide 11


Slide 13



Slide 16

Slide 17



TCP Slow Start




TCP throughput


TCP Fairness

Why is TCP fair

Fairness (more)

Chapter 3 summary

Transport Layer 3-4






a top-10 problem


Transport Layer 3-5





no retransmission



Host A

original data in

Host B

throughputout

R2

R2

out

in R2d

ela

yin


Transport Layer 3-6



= out



Host A

in original data

Host B


retransmitted data

lsquo


Transport Layer 3-7





retransmitted data

copy

free buffer space

R2

R2

out

in


Host B

A

Transport Layer 3-8


retransmitted data

copy

no buffer space




A

Host B

Transport Layer 3-9


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



decreasing goodput

R2in







rsquo increase


Host A out


Host B

Host C

Host D

in original data


retransmitted data







C2

C2

ou

t

inrsquo



controlend-end

congestion control


























RM cell data cell


Chapter 3 outline








control





after loss

cwnd

TC

P s

ende

r co

nges

tion

win

dow

siz

e


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate~~cwnd

RTTbytessec






Host A

one segment

RT

T

Host B

time

two segments

four segments















cwnd gt ssthresh

congestionavoidance


new ACK

dupACKcount++

duplicate ACK

fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start




duplicate ACK


NewACK

NewACK

NewACK





W

W2


RTTbytessec










TCP connection 1


TCP Fairness

TCP connection 2




proportionally R

R



Con

nect

ion

2 th

roug

h pu t














R2






next leaving the





Chapter 3 outline




Slide 7

Slide 8

Slide 9

Slide 10

Slide 11


Slide 13



Slide 16

Slide 17



TCP Slow Start




TCP throughput


TCP Fairness

Why is TCP fair

Fairness (more)

Chapter 3 summary

Transport Layer 3-5





no retransmission



Host A

original data in

Host B

throughputout

R2

R2

out

in R2d

ela

yin


Transport Layer 3-6



= out



Host A

in original data

Host B


retransmitted data

lsquo


Transport Layer 3-7





retransmitted data

copy

free buffer space

R2

R2

out

in


Host B

A

Transport Layer 3-8


retransmitted data

copy

no buffer space




A

Host B

Transport Layer 3-9


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



decreasing goodput

R2in







rsquo increase


Host A out


Host B

Host C

Host D

in original data


retransmitted data







C2

C2

ou

t

inrsquo



controlend-end

congestion control


























RM cell data cell


Chapter 3 outline








control





after loss

cwnd

TC

P s

ende

r co

nges

tion

win

dow

siz

e


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate~~cwnd

RTTbytessec






Host A

one segment

RT

T

Host B

time

two segments

four segments















cwnd gt ssthresh

congestionavoidance


new ACK

dupACKcount++

duplicate ACK

fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start




duplicate ACK


NewACK

NewACK

NewACK





W

W2


RTTbytessec










TCP connection 1


TCP Fairness

TCP connection 2




proportionally R

R



Con

nect

ion

2 th

roug

h pu t














R2






next leaving the





Chapter 3 outline




Slide 7

Slide 8

Slide 9

Slide 10

Slide 11


Slide 13



Slide 16

Slide 17



TCP Slow Start




TCP throughput


TCP Fairness

Why is TCP fair

Fairness (more)

Chapter 3 summary

Transport Layer 3-6



= out



Host A

in original data

Host B


retransmitted data

lsquo


Transport Layer 3-7





retransmitted data

copy

free buffer space

R2

R2

out

in


Host B

A

Transport Layer 3-8


retransmitted data

copy

no buffer space




A

Host B

Transport Layer 3-9


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



decreasing goodput

R2in







rsquo increase


Host A out


Host B

Host C

Host D

in original data


retransmitted data







C2

C2

ou

t

inrsquo



controlend-end

congestion control


























RM cell data cell


Chapter 3 outline








control





after loss

cwnd

TC

P s

ende

r co

nges

tion

win

dow

siz

e


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate~~cwnd

RTTbytessec






Host A

one segment

RT

T

Host B

time

two segments

four segments















cwnd gt ssthresh

congestionavoidance


new ACK

dupACKcount++

duplicate ACK

fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start




duplicate ACK


NewACK

NewACK

NewACK





W

W2


RTTbytessec










TCP connection 1


TCP Fairness

TCP connection 2




proportionally R

R



Con

nect

ion

2 th

roug

h pu t














R2






next leaving the





Chapter 3 outline




Slide 7

Slide 8

Slide 9

Slide 10

Slide 11


Slide 13



Slide 16

Slide 17



TCP Slow Start




TCP throughput


TCP Fairness

Why is TCP fair

Fairness (more)

Chapter 3 summary

Transport Layer 3-7





retransmitted data

copy

free buffer space

R2

R2

out

in


Host B

A

Transport Layer 3-8


retransmitted data

copy

no buffer space




A

Host B

Transport Layer 3-9


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



decreasing goodput

R2in







rsquo increase


Host A out


Host B

Host C

Host D

in original data


retransmitted data







C2

C2

ou

t

inrsquo



controlend-end

congestion control


























RM cell data cell


Chapter 3 outline








control





after loss

cwnd

TC

P s

ende

r co

nges

tion

win

dow

siz

e


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate~~cwnd

RTTbytessec






Host A

one segment

RT

T

Host B

time

two segments

four segments















cwnd gt ssthresh

congestionavoidance


new ACK

dupACKcount++

duplicate ACK

fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start




duplicate ACK


NewACK

NewACK

NewACK





W

W2


RTTbytessec










TCP connection 1


TCP Fairness

TCP connection 2




proportionally R

R



Con

nect

ion

2 th

roug

h pu t














R2






next leaving the





Chapter 3 outline




Slide 7

Slide 8

Slide 9

Slide 10

Slide 11


Slide 13



Slide 16

Slide 17



TCP Slow Start




TCP throughput


TCP Fairness

Why is TCP fair

Fairness (more)

Chapter 3 summary

Transport Layer 3-8


retransmitted data

copy

no buffer space




A

Host B

Transport Layer 3-9


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



decreasing goodput

R2in







rsquo increase


Host A out


Host B

Host C

Host D

in original data


retransmitted data







C2

C2

ou

t

inrsquo



controlend-end

congestion control


























RM cell data cell


Chapter 3 outline








control





after loss

cwnd

TC

P s

ende

r co

nges

tion

win

dow

siz

e


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate~~cwnd

RTTbytessec






Host A

one segment

RT

T

Host B

time

two segments

four segments















cwnd gt ssthresh

congestionavoidance


new ACK

dupACKcount++

duplicate ACK

fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start




duplicate ACK


NewACK

NewACK

NewACK





W

W2


RTTbytessec










TCP connection 1


TCP Fairness

TCP connection 2




proportionally R

R



Con

nect

ion

2 th

roug

h pu t














R2






next leaving the





Chapter 3 outline




Slide 7

Slide 8

Slide 9

Slide 10

Slide 11


Slide 13



Slide 16

Slide 17



TCP Slow Start




TCP throughput


TCP Fairness

Why is TCP fair

Fairness (more)

Chapter 3 summary

Transport Layer 3-9


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



decreasing goodput

R2in







rsquo increase


Host A out


Host B

Host C

Host D

in original data


retransmitted data







C2

C2

ou

t

inrsquo



controlend-end

congestion control


























RM cell data cell


Chapter 3 outline








control





after loss

cwnd

TC

P s

ende

r co

nges

tion

win

dow

siz

e


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate~~cwnd

RTTbytessec






Host A

one segment

RT

T

Host B

time

two segments

four segments















cwnd gt ssthresh

congestionavoidance


new ACK

dupACKcount++

duplicate ACK

fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start




duplicate ACK


NewACK

NewACK

NewACK





W

W2


RTTbytessec










TCP connection 1


TCP Fairness

TCP connection 2




proportionally R

R



Con

nect

ion

2 th

roug

h pu t














R2






next leaving the





Chapter 3 outline




Slide 7

Slide 8

Slide 9

Slide 10

Slide 11


Slide 13



Slide 16

Slide 17



TCP Slow Start




TCP throughput


TCP Fairness

Why is TCP fair

Fairness (more)

Chapter 3 summary


A

in outincopy

free buffer space

timeout

R2

R2in

out


Host B






R2

out



decreasing goodput

R2in







rsquo increase


Host A out


Host B

Host C

Host D

in original data


retransmitted data







C2

C2

ou

t

inrsquo



controlend-end

congestion control


























RM cell data cell


Chapter 3 outline








control





after loss

cwnd

TC

P s

ende

r co

nges

tion

win

dow

siz

e


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate~~cwnd

RTTbytessec






Host A

one segment

RT

T

Host B

time

two segments

four segments















cwnd gt ssthresh

congestionavoidance


new ACK

dupACKcount++

duplicate ACK

fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start




duplicate ACK


NewACK

NewACK

NewACK





W

W2


RTTbytessec










TCP connection 1


TCP Fairness

TCP connection 2




proportionally R

R



Con

nect

ion

2 th

roug

h pu t














R2






next leaving the





Chapter 3 outline




Slide 7

Slide 8

Slide 9

Slide 10

Slide 11


Slide 13



Slide 16

Slide 17



TCP Slow Start




TCP throughput


TCP Fairness

Why is TCP fair

Fairness (more)

Chapter 3 summary


R2

out



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R



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next leaving the





Chapter 3 outline




Slide 7

Slide 8

Slide 9

Slide 10

Slide 11


Slide 13



Slide 16

Slide 17



TCP Slow Start




TCP throughput


TCP Fairness

Why is TCP fair

Fairness (more)

Chapter 3 summary




rsquo increase


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Host B

Host C

Host D

in original data


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win

dow

siz

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for bandwidth


time









last byte sent

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rate~~cwnd

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nect

ion

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next leaving the





Chapter 3 outline




Slide 7

Slide 8

Slide 9

Slide 10

Slide 11


Slide 13



Slide 16

Slide 17



TCP Slow Start




TCP throughput


TCP Fairness

Why is TCP fair

Fairness (more)

Chapter 3 summary





C2

C2

ou

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inrsquo



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congestion control


























RM cell data cell


Chapter 3 outline








control





after loss

cwnd

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ende

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nges

tion

win

dow

siz

e


for bandwidth


time









last byte sent

cwnd


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rate~~cwnd

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Host A

one segment

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T

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time

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four segments















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dupACKcount == 3




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duplicate ACK


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W

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RTTbytessec










TCP connection 1


TCP Fairness

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proportionally R

R



Con

nect

ion

2 th

roug

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R2






next leaving the





Chapter 3 outline




Slide 7

Slide 8

Slide 9

Slide 10

Slide 11


Slide 13



Slide 16

Slide 17



TCP Slow Start




TCP throughput


TCP Fairness

Why is TCP fair

Fairness (more)

Chapter 3 summary



controlend-end

congestion control


























RM cell data cell


Chapter 3 outline








control





after loss

cwnd

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P s

ende

r co

nges

tion

win

dow

siz

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for bandwidth


time









last byte sent

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Host A

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W

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TCP connection 1


TCP Fairness

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proportionally R

R



Con

nect

ion

2 th

roug

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R2






next leaving the





Chapter 3 outline




Slide 7

Slide 8

Slide 9

Slide 10

Slide 11


Slide 13



Slide 16

Slide 17



TCP Slow Start




TCP throughput


TCP Fairness

Why is TCP fair

Fairness (more)

Chapter 3 summary




















RM cell data cell


Chapter 3 outline








control





after loss

cwnd

TC

P s

ende

r co

nges

tion

win

dow

siz

e


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate~~cwnd

RTTbytessec






Host A

one segment

RT

T

Host B

time

two segments

four segments















cwnd gt ssthresh

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new ACK

dupACKcount++

duplicate ACK

fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start




duplicate ACK


NewACK

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W

W2


RTTbytessec










TCP connection 1


TCP Fairness

TCP connection 2




proportionally R

R



Con

nect

ion

2 th

roug

h pu t














R2






next leaving the





Chapter 3 outline




Slide 7

Slide 8

Slide 9

Slide 10

Slide 11


Slide 13



Slide 16

Slide 17



TCP Slow Start




TCP throughput


TCP Fairness

Why is TCP fair

Fairness (more)

Chapter 3 summary


Chapter 3 outline








control





after loss

cwnd

TC

P s

ende

r co

nges

tion

win

dow

siz

e


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate~~cwnd

RTTbytessec






Host A

one segment

RT

T

Host B

time

two segments

four segments















cwnd gt ssthresh

congestionavoidance


new ACK

dupACKcount++

duplicate ACK

fastrecovery


duplicate ACK



dupACKcount == 3




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duplicate ACK


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NewACK





W

W2


RTTbytessec










TCP connection 1


TCP Fairness

TCP connection 2




proportionally R

R



Con

nect

ion

2 th

roug

h pu t














R2






next leaving the





Chapter 3 outline




Slide 7

Slide 8

Slide 9

Slide 10

Slide 11


Slide 13



Slide 16

Slide 17



TCP Slow Start




TCP throughput


TCP Fairness

Why is TCP fair

Fairness (more)

Chapter 3 summary





after loss

cwnd

TC

P s

ende

r co

nges

tion

win

dow

siz

e


for bandwidth


time









last byte sent

cwnd


lt cwnd


rate~~cwnd

RTTbytessec






Host A

one segment

RT

T

Host B

time

two segments

four segments















cwnd gt ssthresh

congestionavoidance


new ACK

dupACKcount++

duplicate ACK

fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start




duplicate ACK


NewACK

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NewACK





W

W2


RTTbytessec










TCP connection 1


TCP Fairness

TCP connection 2




proportionally R

R



Con

nect

ion

2 th

roug

h pu t














R2






next leaving the





Chapter 3 outline




Slide 7

Slide 8

Slide 9

Slide 10

Slide 11


Slide 13



Slide 16

Slide 17



TCP Slow Start




TCP throughput


TCP Fairness

Why is TCP fair

Fairness (more)

Chapter 3 summary









last byte sent

cwnd


lt cwnd


rate~~cwnd

RTTbytessec






Host A

one segment

RT

T

Host B

time

two segments

four segments















cwnd gt ssthresh

congestionavoidance


new ACK

dupACKcount++

duplicate ACK

fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start




duplicate ACK


NewACK

NewACK

NewACK





W

W2


RTTbytessec










TCP connection 1


TCP Fairness

TCP connection 2




proportionally R

R



Con

nect

ion

2 th

roug

h pu t














R2






next leaving the





Chapter 3 outline




Slide 7

Slide 8

Slide 9

Slide 10

Slide 11


Slide 13



Slide 16

Slide 17



TCP Slow Start




TCP throughput


TCP Fairness

Why is TCP fair

Fairness (more)

Chapter 3 summary






Host A

one segment

RT

T

Host B

time

two segments

four segments















cwnd gt ssthresh

congestionavoidance


new ACK

dupACKcount++

duplicate ACK

fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start




duplicate ACK


NewACK

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NewACK





W

W2


RTTbytessec










TCP connection 1


TCP Fairness

TCP connection 2




proportionally R

R



Con

nect

ion

2 th

roug

h pu t














R2






next leaving the





Chapter 3 outline




Slide 7

Slide 8

Slide 9

Slide 10

Slide 11


Slide 13



Slide 16

Slide 17



TCP Slow Start




TCP throughput


TCP Fairness

Why is TCP fair

Fairness (more)

Chapter 3 summary















cwnd gt ssthresh

congestionavoidance


new ACK

dupACKcount++

duplicate ACK

fastrecovery


duplicate ACK



dupACKcount == 3




New ACK

slow start




duplicate ACK


NewACK

NewACK

NewACK





W

W2


RTTbytessec










TCP connection 1


TCP Fairness

TCP connection 2




proportionally R

R



Con

nect

ion

2 th

roug

h pu t














R2






next leaving the





Chapter 3 outline




Slide 7

Slide 8

Slide 9

Slide 10

Slide 11


Slide 13



Slide 16

Slide 17



TCP Slow Start




TCP throughput


TCP Fairness

Why is TCP fair

Fairness (more)

Chapter 3 summary





W

W2


RTTbytessec










TCP connection 1


TCP Fairness

TCP connection 2




proportionally R

R



Con

nect

ion

2 th

roug

h pu t














R2






next leaving the





Chapter 3 outline




Slide 7

Slide 8

Slide 9

Slide 10

Slide 11


Slide 13



Slide 16

Slide 17



TCP Slow Start




TCP throughput


TCP Fairness

Why is TCP fair

Fairness (more)

Chapter 3 summary










TCP connection 1


TCP Fairness

TCP connection 2




proportionally R

R



Con

nect

ion

2 th

roug

h pu t














R2






next leaving the





Chapter 3 outline




Slide 7

Slide 8

Slide 9

Slide 10

Slide 11


Slide 13



Slide 16

Slide 17



TCP Slow Start




TCP throughput


TCP Fairness

Why is TCP fair

Fairness (more)

Chapter 3 summary




proportionally R

R



Con

nect

ion

2 th

roug

h pu t














R2






next leaving the





Chapter 3 outline




Slide 7

Slide 8

Slide 9

Slide 10

Slide 11


Slide 13



Slide 16

Slide 17



TCP Slow Start




TCP throughput


TCP Fairness

Why is TCP fair

Fairness (more)

Chapter 3 summary












R2






next leaving the





Chapter 3 outline




Slide 7

Slide 8

Slide 9

Slide 10

Slide 11


Slide 13



Slide 16

Slide 17



TCP Slow Start




TCP throughput


TCP Fairness

Why is TCP fair

Fairness (more)

Chapter 3 summary






next leaving the





Chapter 3 outline




Slide 7

Slide 8

Slide 9

Slide 10

Slide 11


Slide 13



Slide 16

Slide 17



TCP Slow Start




TCP throughput


TCP Fairness

Why is TCP fair

Fairness (more)

Chapter 3 summary

1 john magee 20 february 2014 cs 280: transport layer: congestion control concepts, tcp congestion...

Documents

r2loutcosts of congestion

lostcausescosts of congestion

congestion control concepts

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transportlayer services3

original dataloutlin

rosstransport layer3

connectionoriented transport