SSD 计算机网络 PPT Chapter3

TransportLayer3-1Chapter3TransportLayerE-Mail:[e-mail]:68778865(O)TransportLayer3-2Chapter3:TransportLayerOurgoals:understandprinciplesbehindtransportlayerservices:multiplexing/demultiplexingreliabledatatransferflowcontrolcongestioncontrollearnabouttransportlayerprotocolsintheInternet:UDP:connectionlesstransportTCP:connection-orientedtransportTCPcongestioncontrolTransportLayer3-3Chapter3outline3.1Transport-layerservices3.2Multiplexinganddemultiplexing3.3Connectionlesstransport:UDP3.4Principlesofreliabledatatransfer3.5Connection-orientedtransport:TCPsegmentstructurereliabledatatransferflowcontrolconnectionmanagement3.6Principlesofcongestioncontrol3.7TCPcongestioncontrolTransportLayer3-4Transportservicesandprotocolsprovidelogicalcommunicationbetweenappprocessesrunningondifferenthoststransportprotocolsruninendsystemssendside:breaksappmessagesintosegments,passestonetworklayerrcvside:reassemblessegmentsintomessages,passestoapplayermorethanonetransportprotocolavailabletoappsInternet:TCPandUDPapplicationtransportnetworkdatalinkphysicalapplicationtransportnetworkdatalinkphysicalTransportLayer3-5Transportvs.networklayernetworklayer:logicalcommunicationbetweenhoststransportlayer:logicalcommunicationbetweenprocessesrelieson,enhances,networklayerservicesHouseholdanalogy:12kidssendinglettersto12kidsprocesses=kidsappmessages=lettersinenvelopeshosts=housestransportprotocol=AnnandBillwhodemuxtoin-housesiblingsnetwork-layerprotocol=postalserviceTransportLayer3-6Internettransport-layerprotocolsreliable,in-orderdelivery(TCP)congestioncontrolflowcontrolconnectionsetupunreliable,unordereddelivery:UDPno-frillsextensionof“best-effort”IPWhatdoesUDPprovideinadditiontoIP?servicesnotavailable:delayguaranteesbandwidthguaranteesapplicationtransportnetworkdatalinkphysicalnetworkdatalinkphysicalnetworkdatalinkphysicalnetworkdatalinkphysicalnetworkdatalinkphysicalnetworkdatalinkphysicalnetworkdatalinkphysicalapplicationtransportnetworkdatalinkphysicalTransportLayer3-7Chapter3outline3.1Transport-layerservices3.2Multiplexinganddemultiplexing3.3Connectionlesstransport:UDP3.4Principlesofreliabledatatransfer3.5Connection-orientedtransport:TCPsegmentstructurereliabledatatransferflowcontrolconnectionmanagement3.6Principlesofcongestioncontrol3.7TCPcongestioncontrolMultiplexing/DemultiplexingUsesamecommunicationchannelbetweenhostsforseverallogicalcommunicationprocessesHowdoesMux/DeMuxwork?Sockets:doorsbetweenprocess&hostUDPsocket:(dest.IP,dest.Port)TCPsocket:(src.IP,src.port,dest.IP,dest.Port)TransportLayer3-8TransportLayer3-9Multiplexing/demultiplexingapplicationtransportnetworklinkphysicalP1applicationtransportnetworklinkphysicalapplicationtransportnetworklinkphysicalP2P3P4P1host1host2host3=process=socketdeliveringreceivedsegmentstocorrectsocketDemultiplexingatrcvhost:gatheringdatafrommultiplesockets,envelopingdatawithheader(laterusedfordemultiplexing)Multiplexingatsendhost:TransportLayer3-10HowdemultiplexingworkshostreceivesIPdatagramseachdatagramhassourceIPaddress,destinationIPaddresseachdatagramcarries1transport-layersegmenteachsegmenthassource,destinationportnumberhostusesIPaddresses&portnumberstodirectsegmenttoappropriatesocketsourceport#destport#32bitsapplicationdata(message)otherheaderfieldsTCP/UDPsegmentformatTransportLayer3-11Connectionlessdemultiplexingrecall:createsocketswithhost-localportnumbers:DatagramSocketmySocket1=newDatagramSocket(12534);DatagramSocketmySocket2=newDatagramSocket(12535);recall:whencreatingdatagramtosendintoUDPsocket,mustspecify(destIPaddress,destportnumber)whenhostreceivesUDPsegment:checksdestinationportnumberinsegmentdirectsUDPsegmenttosocketwiththatportnumberIPdatagramswithdifferentsourceIPaddressesand/orsourceportnumbersdirectedtosamesocketTransportLayer3-12Connectionlessdemux(cont)DatagramSocketserverSocket=newDatagramSocket(6428);ClientIP:BP2clientIP:AP1P1P3serverIP:CSP:6428DP:9157SP:9157DP:6428SP:6428DP:5775SP:5775DP:6428SPprovides“returnaddress”TransportLayer3-13Connection-orienteddemuxTCPsocketidentifiedby4-tuple:sourceIPaddresssourceportnumberdestIPaddressdestportnumberrecvhostusesallfourvaluestodirectsegmenttoappropriatesocketserverhostmaysupportmanysimultaneousTCPsockets:eachsocketidentifiedbyitsown4-tuplewebservershavedifferentsocketsforeachconnectingclientnon-persistentHTTPwillhavedifferentsocketforeachrequestTransportLayer3-14Connection-orienteddemux(cont)ClientIP:BP1clientIP:AP1P2P4serverIP:CSP:9157DP:80SP:9157DP:80P5P6P3D-IP:CS-IP:AD-IP:CS-IP:BSP:5775DP:80D-IP:CS-IP:BTransportLayer3-15Connection-orienteddemux:ThreadedWebServerclientIP:BP1clientIP:AP1P2serverIP:CSP:9157DP:80SP:9157DP:80P4P3D-IP:CS-IP:AD-IP:CS-IP:BSP:5775DP:80D-IP:CS-IP:BTransportLayer3-16Chapter3outline3.1Transport-layerservices3.2Multiplexinganddemultiplexing3.3Connectionlesstransport:UDP3.4Principlesofreliabledatatransfer3.5Connection-orientedtransport:TCPsegmentstructurereliabledatatransferflowcontrolconnectionmanagement3.6Principlesofcongestioncon