transport layer3-1 chapter 3 transport layer these ppt slides are originally from the kurose and...

Transport Layer 3-1

Chapter 3Transport Layer

These ppt slides are originally from theKurose and Ross’s book. But some slides aredeleted and added for my own purpose, and some of them are modified.

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 transport layer protocols in the Internet: UDP: connectionless

transport TCP: connection-oriented

transport TCP congestion control

Transport Layer 3-3

TCP/IP Protocol Suite

IP

TCP UDP

FTP Telnet SMTP BGP RIP DNS SNMP

RARPARP

IGMPICMP OSPF

HTTP

Transport Layer 3-4

Chapter 3 outline

3.1 Transport-layer services

3.2 Multiplexing and demultiplexing

3.3 Connectionless transport: UDP

3.4 Principles of reliable data transfer

3.5 Connection-oriented transport: TCP segment structure reliable data transfer flow control connection

management

3.6 Principles of congestion control

3.7 TCP congestion control

Transport Layer 3-5

Transport services and protocols provide logical

communication between app processes running on different hosts

transport protocols run in end systems send side: breaks

app messages into segments, passes to network layer

rcv side: reassembles segments into messages, passes to app layer

application

transportnetworkdata linkphysical

application

transportnetworkdata linkphysical

networkdata linkphysical



networkdata linkphysicalnetwork

data linkphysical

logical end-end transport

Transport Layer 3-6

AnalogySeoul Busan

Consider two houses, one in Seoul and the other in Busan, Four kids live in each house. Each kid write a letter to its cousin who lives in the other house every Sunday. In each house there is one kid(Gilsoo and Bowen)who is responsible for mail collection and mail distribution.

Gilsoo Bowon

Application messageProcessesHostTransport-layer protocolNetwork-layer protocol

Gilsoo and BowonKidsPostal serviceLetterhouse

Transport Layer 3-7

Chapter 3 outline


3.2 Multiplexing and demultiplexing(Addressing of application processes)




management



Transport Layer 3-8

Addressing: Port Number

The address of the application process running on a host is called a port number.

Transport Layer 3-9

IP Address and Port Number

Transport Layer 3-10

The Range of Port Numbers

The port number is 16-bit integers between 0 and 65535. The ephemeral port numbers

The client process defines itself with a port number randomly. The well-known port numbers

The Internet has decided to use universal port numbers for servers.

(ephemeral)


Port Protocol Description

7 Echo Echoes a received datagram back to the sender

9 Discard Discards any datagram that is received

11 Users Active users

13 Daytime Returns the date and the time

17 Quote Returns a quote of the day

19 Chargen Returns a string of characters

20 FTP, Data File Transfer Protocol (data connection)

21 FTP, Control File Transfer Protocol (control connection)

23 TELNET Terminal Network

25 SMTP Simple Mail Transfer Protocol

53 DNS Domain Name Server

67 BOOTP Bootstrap Protocol

79 Finger Finger

80 HTTP Hypertext Transfer Protocol

111 RPC Remote Procedure Call

Well-known port number used by TCP


Well-known port number used by UDP

Port Protocol Description

7 Echo Echoes a received datagram back to the sender

9 Discard Discards any datagram that is received

11 Users Active users

13 Daytime Returns the date and the time

17 Quote Returns a quote of the day

19 Chargen Returns a string of characters

53 Nameserver Domain Name Service

67 Bootps Server port to download bootstrap information

68 Bootpc Client port to download bootstrap information

69 TFTP Trivial File Transfer Protocol

111 RPC Remote Procedure Call

123 NTP Network Time Protocol

161 SNMP Simple Network Management Protocol

162 SNMP Simple Network Management Protocol (trap)


Socket Address

Process-to-process delivery needs two identifiers, IP address and the port number, at each end to make a connection.

The combination of an IP address and a port number is called a socket address, which defines the destination process uniquely.


Protocol Stack

AP

Application processes

IPLink/physical

layers

Data communication network

Host

Port number

Protocol number

TCP/UDP

IPLink/phisical

layers

Host

Port number

Protocol number

TCP/UDP

AP AP AP

Application processes

AP AP


Example(Web server)


Reliable vs. Unreliable Service If the application-layer program needs reliability, we use a

reliable transport protocol. If the application has its own flow and error control

mechanism or it needs faster service or the kind of a service that does not demand flow and error control(ex, real-time application), then unreliable transport can be used.

networkaccess 1

IP

TCP/UDP

Application

networkAccess 2

IP

TCP/UDP

Application

network networkaccess1 access2

IP

subnet 1

End-to-end Service

subnet 2


Transport protocol Functions:Reliable vs. Unreliable Unreliable Transport protocol functions

Addressing for application processes(multiplexing)

Reliable Transport Protocol functions Address for application processes Error control (retransmission) Flow control Guarantee of no out-of-sequence of packet order No duplication


Chapter 3 outline


3.2 Multiplexing and demultiplexing




management




UDP: User Datagram Protocol [RFC 768]

“no frills,” “bare bones” Internet transport protocol

“best effort” service, UDP segments may be: lost delivered out of order

to app connectionless:

no handshaking between UDP sender, receiver

each UDP segment handled independently of others

Why is there a UDP? no connection

establishment (which can add delay)

simple: no connection state at sender, receiver

small segment header no congestion control:

UDP can blast away as fast as desired


UDP: more

often used for streaming multimedia apps loss tolerant rate sensitive

other UDP uses DNS SNMP

reliable transfer over UDP: add reliability at application layer application-specific

error recovery!

source port # dest port #

32 bits

Applicationdata

(message)

UDP segment format

length checksumLength, in

bytes of UDPsegment,including

header


UDP checksum

Sender: treat segment contents

as sequence of 16-bit integers

checksum: addition (1’s 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: NO - error detected YES - no error detected.

But maybe errors nonetheless? More later ….

Goal: detect “errors” (e.g., flipped bits) in transmitted segment


Internet Checksum Example Note

When adding numbers, a carryout from the most significant bit needs to be added to the result

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

transport layer3-1 chapter 3 transport layer these ppt slides are originally from the kurose and...

Documents