Architecture
Thearchitectureofapacketswitchconsistsofaswitchingunit,aninterfaceunitandacontrolunit.
Switchingunit
Thefunctionperformedbytheswitchingunitofthepacketswitchisalsothebasicfunctionoftheswitchingunit,thatis,informationissentfromacertaininputporttoacertainoutputport,butpacketswitchingThecharacteristicdeterminesthattheprocessingprocessoftheswitchingunitofthepacketswitchissignificantlydifferentfromtheswitchingunitofthecircuitswitch.First,duetotheburstynatureofpacketswitchingdata,theremaybemessagequeuesattheinputportandoutputportoftheswitchingunit,sotheswitchingunitneedstobuffertheinformation;secondly,thepacketswitchingusesastatisticaltimedivisionmultiplexingmethod.Sincestatisticaltimedivisionmultiplexingdistinguishesusersthroughidentification,theswitchingunitofthepacketswitchneedstoanalyzethecorrespondingidentificationinthepacketheaderandusethisasthebasisforrouting.Theroadisdifferent.
Generallyspeaking,whentheprocessingspeedisnothigh,acomputercanbeusedtocompletethefunctionoftheexchangeunit.Onlywhenthecapacityoftheswitchingunitistoolarge,theuseofadedicatedhardwareswitchingunitwillbeconsidered.
Interfaceunit
Theinterfaceunitincludestheinterfaceunitoftheusersidelineandtheinterfaceunitofthetrunksideline.Themainfunctionsitcompletesinclude:monitoringandcontrolofusersideaccess,groupinganddecomposition,errorcontrol,transmissioncontrol,etc.
Controlunit
Thecontrolunitisusedtocompletethecontroloftheentiresystem,anditsfunctionsinclude:callprocessing,flowcontrol,routing,systemconfigurationandmanagement,etc.Thefunctionofthecontrolunitisgenerallycompletedbysoftware.
Performanceindicators
Themainperformanceindicatorsofpacketswitchesare:
(1)Throughput
Thenumberofgroupsisexpressed.Accordingtothethroughput,packetswitchescanbedividedinto:low-speedpacketswitches(lessthan50packets/s),medium-speedpacketswitches(50~500packets/s)andhigh-speedpacketswitches(greaterthan500packets/s).
(2)Averagepacketprocessingdelay
Itreferstotheaverageprocessingtimerequiredtotransmitadatapacketfromtheinputporttotheoutputport.
(3)Virtualcallprocessingcapability
Thenumberofvirtualcallsthatcanbeprocessedwithinaunittime.
Inaddition,thenumberofportsofpacketswitches,thenumberofchannels,linkspeed,theabilitytoprovideuserswithoptionalsupplementaryservices,theabilitytoprovidenon-standardinterfaces,andreliabilityarealsoperformanceindicatorsthatareoftenconsidered.
Exampleanalysis
DPN-100isatypicalpacketswitch.
TheDPN-100packetswitchadoptsamodularstructure.Thebasicmodulesare:accessmodule(AM)andresourcemodule(RM).Theaccessmoduleprovidesuseraccessanddataexchangeservicesofdifferentprocedures,andtheRMprovidesexchangecontrolandroutingselectionfunctions.TheconnectionbetweentheRMofoneswitchandtheRMofanotherswitchiscalledatrunk,anditsratecanreach2.048Mbit/s;theconnectionbetweenRMandAMandbetweenAMandAMiscalledlink(link),theprosecutionratecanreach256kbit/s;theconnectionbetweentheAMandtheuseriscalledasubscriberline,anditsratecanreach64kbit/s.
ThehardwarestructureofAMandRMaresimilar,includingthesamecommoncomponents:commonmemory(CM),dualbus,processorunit(PE),peripheralinterface(PI).
CMisusedtocompletethecommunicationbetweeneachprocessorunit,andisalsoresponsibleformanagingthecompetitioncausedbyeachPErequestingtheuseofthebus.EachmodulemustcontaintwoCMs,oneofwhichisusedforhotbackup.
PEprovidestheprocessingfunctionofthemodule,andrealizesdifferentfunctionsbyloadingdifferentsoftware,includingmanagementprocessorunit(OPE),serviceprocessorunit(SPE),useraccessprocessorunitandrelayCircuitprocessorunit,etc.
PIprovidesthephysicalportoftheaccessmodule.AlldataenteringandexitingAMandRMmustpassthroughPI,butPIdoesnotprocesshumanandinformation,butdirectlysendstheinformationtoPEforprocessing.