《计算机网络——自顶向下方法与Internet特色》幻灯片Lecture31.ppt
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1、Chapter 3:Transport LayerOur goals:understand principles behind transport layer services:multiplexing/demultiplexingreliable data transferflow controlcongestion controllearn about transport layer protocols in the Internet:UDP:connectionless transportTCP:connection-oriented transportTCP congestion co
2、ntrolChapter 3 outline3.1 Transport-layer services3.2 Multiplexing and demultiplexing3.3 Connectionless transport:UDP3.4 Principles of reliable data transfer3.5 Connection-oriented transport:TCPsegment structurereliable data transferflow controlconnection management3.6 Principles of congestion contr
3、ol3.7 TCP congestion control3.1 Transport services and protocolsprovide logical communication between app processes running on different hoststransport protocols run in end systems send side:breaks app messages into segments,passes to network layerrcv side:reassembles segments into messages,passes t
4、o app layermore than one transport protocol available to appsInternet:TCP and UDPapplicationtransportnetworkdata linkphysicalapplicationtransportnetworkdata linkphysicalnetworkdata linkphysicalnetworkdata linkphysicalnetworkdata linkphysicalnetworkdata linkphysicalnetworkdata linkphysicallogical end
5、-end transport3.1.1 Transport work layernetwork layer:logical communication between hoststransport layer:logical communication between processes relies on,enhances,network layer servicesHousehold analogy:12 kids sending letters to 12 kidsprocesses=kidsapp messages=letters in envelopeshosts=housestra
6、nsport protocol=Ann and Billnetwork-layer protocol=postal service3.1.2 Internet transport-layer protocolsTCP(Transmission Control Protocol)and UDP(User Datagram Protocol)Segment and Datagram(also used in Network layer)Internets Network Layer protocol-IP(Internet Protocol).IP provides logical communi
7、cation between hosts.The IP service model is a best-effort delivery service(尽力而为交互服务).The most fundamental responsibility of UDP and TCP is to extend IPs delivery service between two end system to a delivery service between two processes running on the end systems.Extending host-to-host delivery to
8、process-to-process delivery is called transport layer multiplexing(多路复用)and demultiplexing(多路分解).3.1.2 Internet transport-layer protocolsreliable,in-order delivery(TCP)congestion control flow controlconnection setupunreliable,unordered delivery:UDPno-frills extension of“best-effort”IPservices not av
9、ailable:delay guaranteesbandwidth guaranteesapplicationtransportnetworkdata linkphysicalapplicationtransportnetworkdata linkphysicalnetworkdata linkphysicalnetworkdata linkphysicalnetworkdata linkphysicalnetworkdata linkphysicalnetworkdata linkphysicallogical end-end transportChapter 3 outline3.1 Tr
10、ansport-layer services3.2 Multiplexing and demultiplexing3.3 Connectionless transport:UDP3.4 Principles of reliable data transfer3.5 Connection-oriented transport:TCPsegment structurereliable data transferflow controlconnection management3.6 Principles of congestion control3.7 TCP congestion control
11、3.2 Multiplexing/demultiplexingapplicationtransportnetworklinkphysicalP1applicationtransportnetworklinkphysicalapplicationtransportnetworklinkphysicalP2P3P4P1host 1host 2host 3=process=socketdelivering received segmentsto correct socketDemultiplexing at rcv host:gathering data from multiplesockets,e
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