网络平台与交换技术优秀文档

1.5网络平台与交换技术

网络平台是计算机网络的枢纽，它由传输设备，

交换设备，网络互联设备，布线系统，操作系统等组成。

网络平台传输

交换

网络互联

布线系统

网络接入

网络测试

网络服务器交换方法SwitchingCircuitswitchingMessageswitchingPacketswitchingDatagramVirtualcircuitswitching(1)CircuitswitchingIAdedicatedcommunicationpathbetweentwostations.Thatpathisaconnectedsequenceoflinks.Oneachphysicallink,achannelisdedicatedtotheconnection.Example:Telephonesystem.Threephases: Circuitestablishment.DatatransferCircuitdisconnectionCircuit-SwitchedNetworkCircuitswitchingIICircuitswitchingcanberatherinefficient.Channelcapacityisdedicated.Thereisadelaypriortodatatransferforcallestablishment.DataaretransmittedatafixeddataratewithnodelaySwitch(2)MessageswitchingIIfastationwishestosendamessage.Itappendsadestinationaddresstothemessage.Themessageisthenpassedthroughthenetworkfromnodetonode.Ateachnode,theentiremessageisreceived,storedbriefly,andthentransmittedtothenextnode.MessageSwitchingMessageswitchingIIAmessage-switchingnodeistypicallyageneral-purposemicrocomputer,withsufficientstoragetobuffermessageastheycomein.Delay:Thetimerequiredtoreceiveallbitsofthemessage+Aqueuingdelaywaitingforanopportunitytoretransmittothenextnode.Store-and-forwardmessagesystem.MS:AdvantagesGreaterlineefficiencyAvailabilityofbothendsisnotrequired.Whentrafficisheavy,messagesarestillaccepted.Multicastiseasy.MessageprioritiesErrorcontrolandrecoveryprocedurescanbebuiltintothenetwork.Speedandcodeconversion.Messagessenttoinoperativeterminalsmaybeinterceptedandeitherstoredorreroutedtootherterminals.MS:DisadvantageItisnotsuitedtoreal-timeorinteractivetraffic.Thedelayisrelativelongandhasrelativelyhighvariance.Itcannotbeusedforvoiceconnections.Itisnotsuitedtointeractiveterminal-hostconnections.(3)PacketswitchingEachmessagetobetransmittedthroughthenetworkisfirstlydividedintoanumberofsmallermessageunitknownaspacket.DatagramapproachVirtualCircuitForamoderatetoheavyload,packetswitchingistobepreferred.Messagessenttoinoperativeterminalsmaybeinterceptedandeitherstoredorreroutedtootherterminals.Example:Telephonesystem.PacketsizeThenodemakearoutingdecisionforeachpacket.SwitchedVirtualCircuitEachpacketcontainsaddressinginformation.SwitchedVirtualCircuitRelievethestationsofunnecessarycommunicationprocessingfunctions.Acomparisonofcircuitswitchedandpacket-switchednetworks.MS:DisadvantageThemessageisthenpassedthroughthenetworkfromnodetonode.DataaretransmittedatafixeddataratewithnodelayCircuit-SwitchedNetworkDatagramApproachMulticastiseasy.网络平台传输

交换

网络互联

布线系统

网络接入

网络测试

网络服务器DatagramApproachDatagramApproach,MultipleChannelsSwitchedVirtualCircuitSwitchedVirtualCircuitSwitchedVirtualCircuitAcomparisonofcircuitswitchedandpacket-switchednetworks.VirtualCircuitCircuit-SwitchedNetworkVirtualcircuitswitchingItisnotsuitedtointeractiveterminal-hostconnections.Advantages:Sequencing,Errorcontrol,FlowcontrolEachpacketistreatedindependently.MessageprioritiesPacketsizeItcannotbeusedforvoiceconnections.Foramoderatetoheavyload,packetswitchingistobepreferred.Thereisadelaypriortodatatransferforcallestablishment.DatagramapproachEachpacketistreatedindependently.Eachpacketcontainsaddressinginformation.Thenodemakearoutingdecisionforeachpacket.Advantages:Thecallsetupphaseisavoided.

Moreprimitive,flexible,andreliableThereisadelaypriortodatatransferforcallestablishment.Errorcontrolandrecoveryprocedurescanbebuiltintothenetwork.Virtualcircuitpacketswitchingisgoodforlongexchangeandrelievingstationsofprocessingburden.Thenodemakearoutingdecisionforeachpacket.Numberandarrangementofnodes.Thatpathisaconnectedsequenceoflinks.Advantages:Errorcontrolandrecoveryprocedurescanbebuiltintothenetwork.PacketsizeForlightand/orintermittentloads,circuitswitchingisthemostcosteffective(PublicTelephoneSystem)PacketsizeFDM(FrequencyDivisionMultiplexing)DatagramapproachVirtualcircuitapproachThereisadelaypriortodatatransferforcallestablishment.VirtualCircuitVirtualcircuitapproachAlogicalconnectionisestablishedbeforeanypacketsaresent.Aroutebetweenstationsissetuppriortodatatransfer.VirtualcircuitapproachAdvantages:Begoodforlongexchange.Relievethestationsofunnecessarycommunicationprocessingfunctions.Services:Sequencing,Errorcontrol,FlowcontrolPacketSwitchThreetypesofdelay:PropagationdelayTransmissiontimeNodedelayPacketSwitchPerformancefactors:Numberofstations.Numberandarrangementofnodes.Totalloadonsystem.Lengthoftypicalexchange.Processingspeedofthenodes.PacketsizeSummaryIForinteractivetraffic,messageswitchingisnotappropriate.Forlightand/orintermitte