《计算机网络与通讯》课程教学资源（PPT课件讲稿，英文版）Chapter 3 Transport Layer

Chapter 3: Transport Layer Chapter goals: Chapter Overview: o understand principles o transport layer services behind transport layer o multiplexing/demultiplexing services: o connectionless transport: UDP o multiplexing/demultiplex Ing o principles of reliable data transfer o reliable data transfer o flow control o connection-oriented transport o congestion control TCP g instantiation and o reliable transfer implementation in the f| ow contro Internet o connection management o principles of congestion contro o TCP congestion control

Comp 361, Spring 2005 3: Transport Layer 1 Chapter 3: Transport Layer last revised 16/03/05 Chapter goals:  understand principles behind transport layer services:  multiplexing/demultiplex ing  reliable data transfer  flow control  congestion control  instantiation and implementation in the Internet Chapter Overview:  transport layer services  multiplexing/demultiplexing  connectionless transport: UDP  principles of reliable data transfer  connection-oriented transport: TCP  reliable transfer  flow control  connection management  principles of congestion control  TCP congestion control

Chapter 3 outline D 3.1 Transport-layer 0 3.5 Connection-oriented services transport: TCP 03.2 Multiplexing and o segment structure demultiplexing o reliable data transfer 03. 3 Connectionless flow control transport: UDP o connection management O 3.4 Principles of 口36 Principles of reliable data transfer congestion control 口3.7 TCP congestion contro

Comp 361, Spring 2005 3: Transport Layer 2 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 services and protocols o provide logical communication lication between app processes running on different hosts data link networ data link o transport protocols run in end systems o send side: breaks app network data link messages into segments physical passes to network layer o rcv side: reassembles segments into messages application passes To app layer networ data link o more than one transport protocol available to apps o Internet: tcp and UDP

Comp 361, Spring 2005 3: Transport Layer 3 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  more than one transport protocol available to apps  Internet: TCP and UDP application transport network data link physical application transport network data link physical network data link physical network data link physical network data link physical network data link network physical data link physical

Transport vs. network layer o network layer: logical Household analogy: communication 12 kids sending letters to between hosts 12 kids O transport layer: logical o processes kids communication D app messages letters between processes in envelopes o relies on, enhances g hosts houses network layer services 口 transport protocol Ann and Bil o network-layer protocol E postal service

Comp 361, Spring 2005 3: Transport Layer 4 Transport vs. network layer  network layer: logical communication between hosts  transport layer: logical communication between processes  relies on, enhances, network layer services Household analogy: 12 kids sending letters to 12 kids  processes = kids  app messages = letters in envelopes  hosts = houses  transport protocol = Ann and Bill  network-layer protocol = postal service

Transport-layer protocols Internet transport services: lication g reliable. in-order unicast data link networ delive ry (TCp) data link o congestion o flow contro o connection setup be, physical i network data link a unreliable (best-effort physical unordered unicast or 受 multicast delivery: UDP o services not available application o real-time networ data link o bandwidth guarantees o reliable multicast

Comp 361, Spring 2005 3: Transport Layer 5 Transport-layer protocols Internet transport services:  reliable, in-order unicast delivery (TCP)  congestion  flow control  connection setup  unreliable (“best-effort”), unordered unicast or multicast delivery: UDP  services not available:  real-time  bandwidth guarantees  reliable multicast application transport network data link physical application transport network data link physical network data link physical network data link physical network data link physical network data link network physical data link physical

Chapter 3 outline 口31 Transport-ayer d3.5 Connection-oriented services transport: TCP 口3.2 Multiplexing and o segment structure demultiplexing o reliable data transfer 03. 3 Connectionless flow control transport: UDP o connection management O 3.4 Principles of 口36 Principles of reliable data transfer congestion control 口3.7 TCP congestion contro

Comp 361, Spring 2005 3: Transport Layer 6 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

Multiplexing/demultiplexing Demultiplexing at rcy host: Multiplexing at send host: delivering received segments gathering data from multiple to correct socket sockets, enveloping data with header later used for demultiplexing) = socket process application P3 P1 application(P2 P4) application fransport fransport fransport network network network link link physical physical SIca host 1 host 2 host 3

Comp 361, Spring 2005 3: Transport Layer 7 Multiplexing/demultiplexing application transport network link physical P1 application transport network link physical application transport network link physical P3 P2 P4 P1 host 1 host 2 host 3 = socket = process delivering received segments to correct socket Demultiplexing at rcv host: gathering data from multiple sockets, enveloping data with header (later used for demultiplexing) Multiplexing at send host:

Multiplexing/demultiplexing segment- unit of data exchanged between Demultiplexing: delivering received segments to transport layer entities correct app layer processes o aka TPDU: transport protocol data unit receiver P3 application-layer P4 M(M data application segment trarsport P2 eader M M net work tion application segment→世M transport transport Hnl Metwork network

Comp 361, Spring 2005 3: Transport Layer 8 application transport network M P2 application transport network Multiplexing/demultiplexing segment - unit of data exchanged between transport layer entities  aka TPDU: transport protocol data unit receiver Ht Hn Demultiplexing: delivering received segments to correct app layer processes segment segment M application transport network P1 M M M P3 P4 segment header application-layer data

How demultiplexing works o host receives IP datagrams o each datagram has source 32 bits IP address destination ip address source port dest port o each datagram carries 1 transport-layer segment other header fields o each segment has source destination port number (recall: well-known port application numbers for specific data applications. ( message) o host uses IP addresses& port numbers to direct segment to appropriate socket TCP/UDP segment format

Comp 361, Spring 2005 3: Transport Layer 9 How demultiplexing works  host receives IP datagrams  each datagram has source IP address, destination IP address  each datagram carries 1 transport-layer segment  each segment has source, destination port number (recall: well-known port numbers for specific applications)  host uses IP addresses & port numbers to direct segment to appropriate socket source port # dest port # 32 bits application data (message) other header fields TCP/UDP segment format

Connectionless demultiplexing o Create sockets with port g When host receives UDP numbers: segment DatagramSocket mySocketl =new o checks destination port DatagramSocket(99111)i number in segment DatagramSocket my Socket=new o directs UDP segment to DatagramSocket(99222)i socket with that port O UDP socket identified by number two-tuple 口 iP datagrams with (dest IP address, dest port number) different source IP addresses and/or source port numbers directed to same socket

Comp 361, Spring 2005 3: Transport Layer 10 Connectionless demultiplexing  Create sockets with port numbers: DatagramSocket mySocket1 = new DatagramSocket(99111); DatagramSocket mySocket2 = new DatagramSocket(99222);  UDP socket identified by two-tuple: (dest IP address, dest port number)  When host receives UDP segment:  checks destination port number in segment  directs UDP segment to socket with that port number  IP datagrams with different source IP addresses and/or source port numbers directed to same socket