ymqi+18-网际协议.ppt

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1、Chapter18InternetProtocols网际协议Overview18.1BasicProtocolFunctions18.2PrincipleofInternetworking18.3ConnectionlessInternetworking18.4InternetProtocol18.5IPv618.1BasicProtocolFunctionsEncapsulation封装Fragmentationandreassembly分片和重装Connectioncontrol连接控制Ordereddelivery顺序交付Flowcontrol流量控制Errorcontr

2、ol差错控制Addressing寻址Multiplexing复用Transmissionservices传输服务Encapsulation封装DatausuallytransferredinblocksProtocoldataunits(PDUs)EachPDUcontainsdataandcontrolinformationAdditionofcontrolinformationtodataisencapsulationThreecategoriesofcontrolAddress：Ofsenderand/orreceiverError-detectingcode：E.g.F

3、CSProtocolcontrol:AdditionalinformationtoimplementprotocolfunctionsFragmentation分片Whyfragment?CommunicationsnetworkmayonlyacceptblocksofuptoacertainsizeMoreefficienterrorcontrol:SmallerretransmissionFairer:PreventstationmonopolizingmediumSmallerbuffersProvisionofcheckpointandrestart/recovery

4、operationsPDUSandFragmentationReassembly重装Segmenteddatamustbereassembledintomessages分片的数据被重新装配成适合应用层需要的信息MorecomplexifPDUsoutoforderConnectionControlLogicalassociation,orconnection,establishedbetweenentitiesThreephasesoccurConnectionestablishmentDatatransferConnectiontermination协议实体面向连接数据传送的

5、各个阶段OrderedDelivery顺序交付PDUsmayarriveoutoforderDifferentpathsthroughnetworkPDUordermustbemaintainedNumberPDUssequentiallyEasytoreorderreceivedPDUsFlowcontrolPerformedbyreceivingentitytolimitamountorrateofdatasentStop-and-waitEachPDUmustbeacknowledgedbeforenextsentCreditAmountofdatathatcanbese

6、ntwithoutacknowledgmentE.g.HDLCsliding-windowErrorControlGuardagainstlossordamageErrordetectionandretransmissionSenderinsertserror-detectingcodeinPDUReceivercheckscodeonincomingPDUIferror,discardIftransmitterdoesn’tgetacknowledgmentinreasonabletime,retransmitErrorcontrolisperformedatvariousl

7、ayersofprotocolBetweenstationandnetworkInsidenetworkAddressingAddressinglevelAddressingscopeConnectionidentifiersAddressingmodeMultiplexing复用通过多个连接进入一个系统的方式也可通过端口名称达成，允许多个并行连接一层到另一层的连接映射运输层的复用IP层端口2端口3端口1运输层复用应用层不同进程的报文通过不同的端口向下交到运输层，再往下就共用网络层提供的服务