计算机网络原理(英文版)课件-Chapter3

Chapter3:TransportLayerOurgoals:understandprinciplesbehindtransportlayerservices:multiplexing/demultiplexingreliabledatatransferflowcontrolcongestioncontrollearnabouttransportlayerprotocolsintheInternet:UDP:connectionlesstransportTCP:connection-orientedtransportTCPcongestioncontrol2/74Chapter3-TransportLayerChapter3outline3.1Transport-layerservices3.2Multiplexinganddemultiplexing3.3Connectionlesstransport:UDP3.4PrinciplesofreliabledatatransferrdtModelGBN（GoBackN）SR（SelectiveRepeat）3.5Connection-orientedtransport:TCPsegmentstructurereliabledatatransferflowcontrolconnectionmanagement3.6Principlesofcongestioncontrol3.7TCPcongestioncontrol3/74Chapter3-TransportLayerTransportservicesandprotocolsprovidelogicalcommunicationbetweenappprocessesrunningondifferenthoststransportprotocolsruninendsystemssendside:breaksappmessagesintosegments,passestonetworklayerrcvside:reassemblessegmentsintomessages,passestoapplayermorethanonetransportprotocolavailabletoappsInternet:TCPandUDPapplicationtransportnetworkdatalinkphysicalapplicationtransportnetworkdatalinkphysicalnetworkdatalinkphysicalnetworkdatalinkphysicalnetworkdatalinkphysicalnetworkdatalinkphysicalnetworkdatalinkphysical4/74Chapter3-TransportLayerTransportvs.networklayernetworklayer:logicalcommunicationbetweenhoststransportlayer:logicalcommunicationbetweenprocessesrelieson,enhances,networklayerservices5/74Chapter3-TransportLayerInternettransport-layerprotocolsreliable,in-orderdelivery(TCP)congestioncontrolflowcontrolconnectionsetupunreliable,unordereddelivery(UDP):no-frillsextensionof“best-effort”IP(不对”尽最大努力服务”的IP协议进行不必要的扩展）servicesnotavailable(QoS):delayguaranteesbandwidthguaranteesapplicationtransportnetworkdatalinkphysicalapplicationtransportnetworkdatalinkphysicalnetworkdatalinkphysicalnetworkdatalinkphysicalnetworkdatalinkphysicalnetworkdatalinkphysicalnetworkdatalinkphysicalQualityofServices6/74Chapter3-TransportLayerChapter3outline3.1Transport-layerservices3.2Multiplexinganddemultiplexing3.3Connectionlesstransport:UDP3.4PrinciplesofreliabledatatransferrdtModelGBN（GoBackN）SR（SelectiveRepeat）3.5Connection-orientedtransport:TCPsegmentstructurereliabledatatransferflowcontrolconnectionmanagement3.6Principlesofcongestioncontrol3.7TCPcongestioncontrol7/74Chapter3-TransportLayerMultiplexing/demultiplexingapplicationtransportnetworklinkphysicalP1applicationtransportnetworklinkphysicalapplicationtransportnetworklinkphysicalP2P3P4P1host1host2host3=process=socketdeliveringreceivedsegmentstocorrectsocketDemultiplexingatrcvhost:gatheringdatafrommultiplesockets,envelopingdatawithheader(laterusedfordemultiplexing)Multiplexingatsendhost:8/74Chapter3-TransportLayerHowdemultiplexingworkshostreceivesIPdatagramseachdatagramhassourceIPaddress,destinationIPaddresseachdatagramcarries1transport-layersegmentIPdatagramformatDATAtypicallyaTCPorUDPsegmentOtherheaderfields32bitsourceIPaddress32bitdestinationIPaddress32bits2B,4.139/74Chapter3-TransportLayerHowdemultiplexingworkshostreceivesIPdatagramseachsegmenthassource,destinationportnumberhostusesIPaddresses&portnumberstodirectsegmenttoappropriatesocketTCP/UDPsegmentformatsourceport#destport#32bitsApplicationdata(message)otherheaderfieldsDATAtypicallyaTCPorUDPsegmentOtherheaderfields32bitsourceIPaddress32bitdestinationIPaddress32bitsIPdatagramformat10/74Chapter3-TransportLayerConnectionlessdemultiplexingCreatesocketswithportnumbers:DatagramSocketmySocket1=newDatagramSocket(99111);DatagramSocketmySocket2=newDatagramSocket(99222);UDPsocketidentifiedbytwo-tuple:(destIPaddress,destportnumber)WhenhostreceivesUDPsegment:checksdestinationportnumberinsegmentdirectsUDPsegmenttosocketwiththatportnumberIPdatagramswithdifferentsourceIPaddressesand/orsourceportnumbersdirectedtosamesocket11/74Chapter3-TransportLayerConnectionlessdemux(cont)DatagramSocketserverSocket=newDatagramSocket(6428);ClientIP:B9157P2clientIP:AP15775P16428P3serverIP:CSP:6428DP:9157dataSP:9157DP:6428dataSP:6428DP:5775dataSP:5775DP:6428dataSPprovides“returnaddress”12/74Chapter3-TransportLayerConnection-orienteddemuxTCPsocketidentifiedby4-tuple:sourceIPaddresssourceportnumberdestIPaddressdestportnumberrecvhostusesallfourvaluestodirectsegmenttoappropriatesocketServerhostmaysupportmanysimultaneousTCPsockets:eachsocketidentifiedbyitsown4-tupleWebservershavedifferentsocketsforeachconnectingclient13/74Chapter3-TransportLayerConnection-orienteddemux(cont)ClientIP:B9157P1clientIP:AP15775P280P4serverIP:CSP:9157DP:80SP:9157DP:8080P580P69157P3D-IP:CS-IP:AD-IP:CS-IP:BSP:5775DP:80D-IP:CS-IP:BWebServerThread/subprocess14/74Chapter3-TransportLayerChapter3outline3.1Transport-layerservices3.2Multiplexinganddemultiplexing3.3Connectionlesstransport:UDP3.4PrinciplesofreliabledatatransferrdtModelGBN（GoBackN）SR（SelectiveRepeat）3.5Connection-orientedtransport:TCPsegmentstructurereliabledatatransferflowcontrolconnectionmanagement3.6Principlesofcongestioncontrol3.7TCPcongestioncontrol15/74Chapter3-TransportLayerUDP:Use