8 Transport_layers_0403_2014

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1、IntroductiontoComputerNetworksTransportLayerProtocolsAllrightsreserved.Nopartofthispublicationandfilemaybereproduced,storedinaretrievalsystem,ortransmittedinanyformorbyanymeans,electronic,mechanical,photocopying,recordingorotherwise,withoutpriorwrittenpermissionofProfessorNen-FuHuang(E-m

2、ail:nfhuang@cs.nthu.edu.tw).OutlineIntroductiontoend-to-endprotocolsSimpleDemultiplexerprotocol(UDP)ReliableByteStreamprotocol(TCP)Transport_Protocols-2End-to-endProtocolsAtransportprotocolisusuallyexpectedtoprovideGuaranteedmessagedeliveryDeliversmessagesinthesameordertheyweresent

3、DeliversatmostonecopyofeachmessageSupportsarbitrarilylargemessagesSupportssynchronizationbetweenthesenderandthereceiverAllowsthereceivertoapplyflowcontroltothesenderSupportsmultipleapplicationprocessesoneachhostTransport_Protocols-3End-to-endProtocolsTypicallimitationsofthenetworkser

4、vice(likeIPofInternet)onwhichtransportprotocolwilloperateDropmessagesReordermessagesDeliverduplicatecopiesofagivenmessageLimitmessagestosomefinitesizeDelivermessagesafteranarbitrarilylongdelayUnreliableserviceTransport_Protocols-4End-to-endProtocolsChallengeforTransportProtocolsDe

5、velopalgorithmsthatturntheunreliableserviceoftheunderlyingnetworkintotheservicerequiredbyapplicationprogramsUnreliableserviceUnreliableservice(UDP)UnreliableserviceReliableservice(TCP)Transport_Protocols-5OutlineIntroductiontoend-to-endprotocolsSimpleDemultiplexerprotocol(UDP)Relia

6、bleByteStreamprotocol(TCP)Transport_Protocols-6SimpleDemultiplexer(UDP)Extendshost-to-hostdeliveryserviceoftheunderlyingnetworkintoaprocess-to-processcommunicationserviceAddsalevelofdemultiplexingwhichallowsmultipleapplicationprocessesoneachhosttosharethenetworkTransport_Protocols-7Simp

7、leDemultiplexer(UDP)081631SrcPortDstPortChecksumLengthDataFormatforUDPheaderTransport_Protocols-8SimpleDemultiplexer(UDP)ApplicationApplicationApplicationProcessProcessProcessPortZPortYPortXQueuesUDPUDPPacketDemultiplexerTransport_Protocols-9OutlineIntroductiontoen