Tanenbaum《计算机网络》原版课件第6章

TheTransportLayerChapter6TheTransportService•ServicesProvidedtotheUpperLayers•TransportServicePrimitives•BerkeleySockets•AnExampleofSocketProgramming:–AnInternetFileServerServicesProvidedtotheUpperLayersThenetwork,transport,andapplicationlayers.TransportServicePrimitivesTheprimitivesforasimpletransportservice.TransportServicePrimitives(2)ThenestingofTPDUs,packets,andframes.TransportServicePrimitives(3)Astatediagramforasimpleconnectionmanagementscheme.Transitionslabeledinitalicsarecausedbypacketarrivals.Thesolidlinesshowtheclient'sstatesequence.Thedashedlinesshowtheserver'sstatesequence.BerkeleySocketsThesocketprimitivesforTCP.SocketProgrammingExample:InternetFileServerClientcodeusingsockets.6-6-1SocketProgrammingExample:InternetFileServer(2)Clientcodeusingsockets.ElementsofTransportProtocols•Addressing•ConnectionEstablishment•ConnectionRelease•FlowControlandBuffering•Multiplexing•CrashRecoveryTransportProtocol(a)Environmentofthedatalinklayer.(b)Environmentofthetransportlayer.AddressingTSAPs,NSAPsandtransportconnections.ConnectionEstablishmentHowauserprocessinhost1establishesaconnectionwithatime-of-dayserverinhost2.ConnectionEstablishment(2)(a)TPDUsmaynotentertheforbiddenregion.(b)Theresynchronizationproblem.ConnectionEstablishment(3)Threeprotocolscenariosforestablishingaconnectionusingathree-wayhandshake.CRdenotesCONNECTIONREQUEST.(a)Normaloperation,(b)OldCONNECTIONREQUESTappearingoutofnowhere.(c)DuplicateCONNECTIONREQUESTandduplicateACK.ConnectionReleaseAbruptdisconnectionwithlossofdata.ConnectionRelease(2)Thetwo-armyproblem.ConnectionRelease(3)Fourprotocolscenariosforreleasingaconnection.(a)Normalcaseofathree-wayhandshake.(b)finalACKlost.6-14,a,bConnectionRelease(4)(c)Responselost.(d)ResponselostandsubsequentDRslost.6-14,c,dFlowControlandBuffering(a)Chainedfixed-sizebuffers.(b)Chainedvariable-sizedbuffers.(c)Onelargecircularbufferperconnection.FlowControlandBuffering(2)Dynamicbufferallocation.Thearrowsshowthedirectionoftransmission.Anellipsis(…)indicatesalostTPDU.Multiplexing(a)Upwardmultiplexing.(b)Downwardmultiplexing.CrashRecoveryDifferentcombinationsofclientandserverstrategy.ASimpleTransportProtocol•TheExampleServicePrimitives•TheExampleTransportEntity•TheExampleasaFiniteStateMachineTheExampleTransportEntityThenetworklayerpacketsusedinourexample.TheExampleTransportEntity(2)Eachconnectionisinoneofsevenstates:1.Idle–Connectionnotestablishedyet.2.Waiting–CONNECThasbeenexecuted,CALLREQUESTsent.3.Queued–ACALLREQUESThasarrived;noLISTENyet.4.Established–Theconnectionhasbeenestablished.5.Sending–Theuseriswaitingforpermissiontosendapacket.6.Receiving–ARECEIVEhasbeendone.7.DISCONNECTING–aDISCONNECThasbeendonelocally.TheExampleTransportEntity(3)TheExampleTransportEntity(4)TheExampleTransportEntity(5)TheExampleTransportEntity(6)TheExampleTransportEntity(7)TheExampleTransportEntity(8)TheExampleTransportEntity(9)TheExampleTransportEntity(10)TheExampleasaFiniteStateMachineTheexampleprotocolasafinitestatemachine.Eachentryhasanoptionalpredicate,anoptionalaction,andthenewstate.Thetildeindicatesthatnomajoractionistaken.Anoverbaraboveapredicateindicatethenegationofthepredicate.Blankentriescorrespondtoimpossibleorinvalidevents.TheExampleasaFiniteStateMachine(2)Theexampleprotocolingraphicalform.Transitionsthatleavetheconnectionstateunchangedhavebeenomittedforsimplicity.TheInternetTransportProtocols:UDP•IntroductiontoUDP•RemoteProcedureCall•TheReal-TimeTransportProtocolIntroductiontoUDPTheUDPheader.RemoteProcedureCallStepsinmakingaremoteprocedurecall.Thestubsareshaded.TheReal-TimeTransportProtocol(a)ThepositionofRTPintheprotocolstack.(b)Packetnesting.TheReal-TimeTransportProtocol(2)TheRTPheader.TheInternetTransportProtocols:TCP•IntroductiontoTCP•TheTCPServiceModel•TheTCPProtocol•TheTCPSegmentHeader•TCPConnectionEstablishment•TCPConnectionRelease•TCPConnectionManagementModeling•TCPTransmissionPolicy•TCPCongestionControl•TCPTimerManagement•WirelessTCPandUDP•TransactionalTCPTheTCPServiceModelSomeassignedports.PortProtocolUse21FTPFiletransfer23TelnetRemotelogin25SMTPE-mail69TFTPTrivialFileTransferProtocol79FingerLookupinfoaboutauser80HTTPWorldWideWeb110POP-3Remotee-mailaccess119NNTPUSENETnewsTheTCPServiceModel(2)(a)Four512-bytesegmentssentasseparateIPdatagrams.(b)The2048bytesofdatadeliveredtotheapplicationinasingleREADCALL.TheTCPSegmentHeaderTCPHeader.TheTCPSegmentHeader(2)ThepseudoheaderincludedintheTCPchecksum.TCPConnectionEstablishment(a)TCPconnectionestablishmentinthenormalcase.(b)Callcollision.6-31TCPConnectionManagementModelingThestatesusedintheTCPconnectionmanagementfinitestatemachine.TCPConnectionManagementModeling(2)TCPconnectionmanagementfinitestatemachine.Theheavysolidlineisthenormalpathforaclient.Theheavydashedlineisthenormalpathforaserver.Thelightlinesareunusualevents.Eachtransitionislabeledbytheeventcausingitandtheactionresultingfromit,separatedbyaslash.TCPTransmissionPolicyWindowmanagementinTCP.TCPTransmissionPolicy(2)Sillywindowsyndrome.TCPCongestionControl(a)Afastnetworkfeedingalowcapacityreceiver.(b)Aslownetwo