计算机网络英文版课件：slide 10 The Transport Layer – Part 1

TheTransportLayer–Part1ContentsTheTransportServices(Section6.1)ServicesprovidedbythetransportlayerServiceprimitivesBerkeleysocketsElementsofTransportProtocols(Section6.2)AddressingConnectionestablishment,andreleaseFlowcontrolBufferingMultiplexingCrashrecoveryTheTransportServiceServicesProvidedtotheUpperLayersTransportServicePrimitivesBerkeleySocketsAnExampleofSocketProgramming:AnInternetFileServerServicesProvidedtotheUpperLayersTheultimategoalofthetransportlayeristoprovideefficient,reliable,andcost-effective

servicetoitsusers,normallyprocessesintheapplicationlayer.Toachievethisgoal,thetransportlayermakesuseoftheservicesprovidedbythenetworklayer.Thehardwareand/orsoftwarewithinthetransportlayerthatdoestheworkiscalledthetransportentity.ServicesProvidedtotheUpperLayers(2)Thenetwork,transport,andapplicationlayers.TransportServicePrimitivesTheprimitivesforasimpletransportservice.TransportServicePrimitives(2)ThenestingofTPDUs,packets,andframes.TransportServicePrimitives(3)Astatediagramforasimpleconnectionmanagementscheme.Transitionslabeledinitalicsarecausedbypacketarrivals.Thesolidlinesshowtheclient'sstatesequence.Thedashedlinesshowtheserver'sstatesequence.Thesocketsprogramminginterfacesareinterfacesfromtheupperthreelayers(the"application")intothetransportlayer.Rawsockets：wecanevenbypasstheIPlayercompletelytoreadandwriteourowndatalinklayerframes.physicaldevicedriverandhardwarenetworktransportsessionpresentationapplicationOSImodel1234567datalinkInternetprotocolsuiteIPv4,IPv6TCPUDPapplicationSocketsXTIuserprocesskernelcommunicationsdetailsapplicationdetailsFigure1.14LayersinOSImodelandInternetprotocolsuiteExtractedfromUnixNetworkProgramming,Vol.1,3rd.Ed.,W.Stevens,BerkeleySocketsThesocketprimitivesforTCP.socket()bind()listen()accept()well-knownportblocksuntilconnectionfromclientread()write()read()close()close()read()write()connect()socket()TCPClientTCPServerprocessrequestdata(reply)end-of-filenotificationdata(request)connectionestablishment(TCPthree-wayhandshake)ExtractedfromUnixNetworkProgramming,Vol.1,3rd.Ed.,W.Stevens,Figure4.1SocketfunctionsforelementaryTCPclient/serverSocketProgrammingExample:

InternetFileServerClientcodeusingsockets.6-6-1SocketProgrammingExample:

InternetFileServer(2)Servercodeusingsockets.ElementsofTransportProtocolsAddressingConnectionEstablishmentConnectionReleaseFlowControlandBufferingMultiplexingCrashRecoveryTransportProtocol(a)Environmentofthedatalinklayer.(b)Environmentofthetransportlayer.AddressingTSAPs,NSAPsandtransportconnections.ConnectionEstablishmentThreeprotocolscenariosforestablishingaconnectionusingathree-wayhandshake.CRdenotesCONNECTIONREQUEST.

(a)Normaloperation,

(b)OldCONNECTIONREQUESTappearingoutofnowhere.

(c)DuplicateCONNECTIONREQUESTandduplicateACK.ConnectionReleaseAbruptdisconnectionwithlossofdata.ConnectionRelease(2)Thetwo-armyproblem.ConnectionRelease(3)6-14,a,bFourprotocolscenariosforreleasingaconnection.(a)Normalcaseofathree-wayhandshake.(b)finalACKlost.ConnectionRelease(4)6-14,c,d(c)Responselost.(d)ResponselostandsubsequentDRslost.FlowControlandBuffering(a)Chainedfixed-sizebuffers.(b)Chainedvariable-sizedbuffers.

(c)Onelargecircularbufferperconnection.FlowControlandBuffering(2)Thearrowsshowthedirectionoftransmission.Anellipsis(…)indicatesalostTPDU.Dynamicbufferallocation.Multiplexing(a)Upwardmultiplexing.(b)Downwardmultiplexing.CrashRecoveryDifferentcombinationsofclientandserverstrategy.SummaryTheTransportServicesWhythetransportlayerneededServicesprovidedbythetransportlayer:connection-orientedtransportservice