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1、Lec01introBuildingBlocksNodes:PC,special-purposehardware…h(huán)ostsswitchesLinks:coaxcable,opticalfiber…point-to-pointmultipleaccess■■■(a)(b)2SwitchedNetworkstwoormorenodesconnectedbyalink,ortwoormorenetworksconnectedbyanodeAnetworkcanbedefinedrecursivelyas...3StatisticalMultiplexingOn-demandtime-di
2、visionSchedulelinkonaper-packetbasisPacketsfromdifferentsourcesinterleavedonlinkBufferpacketsthatarecontendingforthelinkBuffer(queue)overflowiscalledcongestion■■■7Inter-ProcessCommunicationTurnhost-to-hostconnectivityintoprocess-to-processcommunication.Fillgapbetweenwhatapplicationsexpectandwha
3、ttheunderlyingtechnologyprovides.8IPCAbstractionsRequest/Replydistributedfilesystemsdigitallibraries(web)Stream-Basedvideo:sequenceofframes1/4NTSC=352x240pixels(352x240x24)/8=247.5KB30fps=7500KBps=60Mbpsvideoapplicationson-demandvideovideoconferencing9WhatGoesWrongintheNetwork?Bit-levelerrors(e
4、lectricalinterference)Packet-levelerrors(congestion)LinkandnodefailuresPacketsaredelayedPacketsaredeliverout-of-orderThirdpartieseavesdrop(intercept)10LayeringUseabstractionstohidecomplexityAbstractionnaturallyleadtolayeringAlternativeabstractionsateachlayer11ProtocolsBuildingblocksofanetworkar
5、chitectureEachprotocolobjecthastwodifferentinterfacesserviceinterface:operationsonthisprotocolpeer-to-peerinterface:messagesexchangedwithpeerTerm“protocol”isoverloadedspecificationofpeer-to-peerinterfacemodulethatimplementsthisinterface12Interfaces13ProtocolMachineryProtocolGraphmostpeer-to-pee
6、rcommunicationisindirectpeer-to-peerisdirectonlyathardwarelevelHost1Host2FileapplicationDigitallibraryapplicationVideoapplicationFileapplicationDigitallibraryapplicationVideoapplication14Machinery(cont)MultiplexingandDemultiplexing(demuxkey)Encapsulation(header/body)HostHostApplicationprogramAp
7、plicationprogramRRPDataDataHHPRRPHHPApplicationprogramApplicationprogramRRPDataRRPDataHHPRRPData15InternetArchitectureDefinedbyInternetEngineeringTaskForce(IETF)HourglassDesignApplicationvsApplicationProtocol(FTP,HTTP)■■■FTPTCPUDP
