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ID:58656254
大小:1.13 MB
页数:59页
时间:2020-10-05
《计算机网络技术及应用ppt课件.ppt》由会员上传分享,免费在线阅读,更多相关内容在教育资源-天天文库。
1、Ch2.3DataSwitchingSwitching:CircuitswitchingStorage-and-forwardswitchingMessageswitchingPacketswitchingWhat’sswitching?Toassignthenetworkresourceaccordingcertainmethod。Suchas:TelephoneWhyswitching?Toimprovetheefficiencyofline。NetworkisnotfullyconnectedandoftenpartiallyconnectedOnFullyCon
2、nectedNetworksCostsoflinksistoohighnnodes:links=n(n-1)/25nodes:10links100nodes:4950linksSimpleSwitchedNetworkSwitchingNetworksLongdistancetransmissionistypicallydoneoveranetworkofswitchednodesNodesnotconcernedwithcontentofdataEnddevicesarestationsComputer,terminal,phone,etc.Acollectionof
3、nodesandconnectionsisacommunicationsnetworkDataroutedbybeingswitchedfromnodetonode1.CircuitSwitchingDedicatedcommunicationpathbetweentwostationsThreephasesEstablishTransferDisconnectMusthaveswitchingcapacityandchannelcapacitytoestablishconnectionMusthaveintelligencetoworkoutroutingCircui
4、tSwitching-ApplicationsInefficientChannelcapacitydedicatedfordurationofconnectionIfnodata,capacitywastedSetup(connection)takestimeOnceconnected,transferistransparentDevelopedforvoicetraffic(phone)Connectionoriented2.1Storage-and-forwardswitchingPrinciplesCircuitswitchingdesignedforvoiceR
5、esourcesdedicatedtoaparticularcallMuchofthetimeadataconnectionisidleDatarateisfixedBothendsmustoperateatthesamerateMessageswitchingAformofStorage-and-forwardswitchingConnectionlessNotimeforSettingupconnectionThesizeofmessageisarbitraryThebigmessageneedsbigspacetostoreThetimewasteforre-se
6、ndmessagePacketswitchingDatatransmittedinsmallpacketsLongermessagessplitintoseriesofpacketsEachpacketcontainsaportionofuserdataplussomecontrolinfoControlinfoRouting(addressing)infoPacketsarereceived,storedbriefly(buffered)andpastontothenextnodeStoreandforwardUseofPacketsAdvantagesLineeff
7、iciencySinglenodetonodelinkcanbesharedbymanypacketsovertimePacketsqueuedandtransmittedasfastaspossibleDatarateconversionEachstationconnectstothelocalnodeatitsownspeedNodesbufferdataifrequiredtoequalizeratesPacketsareacceptedevenwhennetworkisbusyDeliverymayslowdownPrioriti
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