01_6-1_Transport_Layer_Overview

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1、ComputerNetworksTransportLayerOverview(§6.1.2-6.1.4)DavidWetherall(djw@uw.edu)ProfessorofComputerScience&EngineeringWhereweareintheCourse•StartingtheTransportLayer!–BuildsonthenetworklayertodeliverdataacrossnetworksforapplicationswiththedesiredreliabilityorqualityAppl

2、icationTransportNetworkLinkPhysicalComputerNetworks2Recall•Transportlayerprovidesend-to-endconnectivityacrossthenetworkappappTCPTCPIPIPIPIP802.11802.11EthernetEthernetHostRouterHostComputerNetworks3Recall(2)•Segmentscarryapplicationdataacrossthenetwork•Segmentsarecarr

3、iedwithinpacketswithinframesSegment802.11IPTCPApp,e.g.,HTTPPacketFrameComputerNetworks4TransportLayerServices•ProvidedifferentkindsofdatadeliveryacrossthenetworktoapplicationsUnreliableReliableMessagesDatagrams(UDP)BytestreamStreams(TCP)ComputerNetworks5ComparisonofIn

4、ternetTransports•TCPisfull-featured,UDPisaglorifiedpacketTCP(Streams)UDP(Datagrams)ConnectionsDatagramsBytesaredeliveredonce,Messagesmaybelost,reliably,andinorderreordered,duplicatedArbitrarylengthcontentLimitedmessagesizeFlowcontrolmatchesCansendregardlesssendertorec

5、eiverofreceiverstateCongestioncontrolmatchesCansendregardlesssendertonetworkofnetworkstateComputerNetworks6SocketAPI•Simpleabstractiontousethenetwork–The“network”API(reallyTransportservice)usedtowriteallInternetapps–PartofallmajorOSesandlanguages;originallyBerkeley(Un

6、ix)~1983•SupportsbothInternettransportservices(StreamsandDatagrams)ComputerNetworks7SocketAPI(2)•SocketsletappsattachtothelocalnetworkatdifferentportsSocket,Socket,Port#1Port#2ComputerNetworks8SocketAPI(3)•SameAPIusedforStreamsandDatagramsPrimitiveMeaningSOCKETCreatea

7、newcommunicationendpointBINDAssociatealocaladdress(port)withasocketLISTENAnnouncewillingnesstoacceptconnectionsOnlyneededforStreamsACCEPTPassivelyestablishanincomingconnectionCONNECTActivelyattempttoestablishaconnectionTo/FromSEND(TO)SendsomedataoverthesocketformsforR

8、ECEIVE(FROM)ReceivesomedataoverthesocketDatagramsCLOSEReleasethesocketComputerNetworks9Ports•Applicationprocessisidentifiedb