Definition
PVC(PermanentVirtualCircuit)Permanentvirtualcircuit:Twocomputersareconnectedthroughaconnection-orientednetwork.PVCcanwithstandthecomputer'sre-bootstraporpowerfluctuations,inthissenseitispermanent;PVCisvirtualbecauseitputsthepathintheroutingtableinsteadofestablishingaphysicalconnection.
Virtualcircuitisoneoftheservicesprovidedbypacketswitchingnetwork(theotherisdatagramservice).Simplyput,itistoestablishavirtuallogicalconnectionbetweenuserhoststhroughthecontrolmechanisminsidethenetwork,Andtoensurethecorrectnessandsequenceofthetransmissionoftheenvelope,theestablishmentandremovalofthevirtualcircuitbeforeandafterthecommunication.Apermanentvirtualcircuitisavirtualcircuitthatisestablishedwhenthenetworkisinitialized,andthevirtualcircuitisalwaysmaintained.BothX.25networksandB-ISDNprovidepermanentvirtualcircuitservices.
Features
Virtualcircuitcommunicationissimilartocircuitswitching.Bothareconnection-oriented,thatis,dataissentinthecorrectorder,andadditionaloverheadisrequiredduringtheconnectionestablishmentphase.However,circuitswitchingprovidesstablebitrateanddelaytime,whilethebitrateanddelaytimeofvirtualcircuitservicesdependonthefollowingfactors:
1.Thelengthofthepacketqueueonthenetworknode.
2.Thebitrateofthedatageneratedbytheapplication.
3.Whenusingstatisticalmultiplexingtechnology,theloadofotheruserssharingthesamenetworkresources.
4.Manyvirtualcircuitprotocolsprovidereliablecommunicationservicesthroughdataretransmission,includingerrordetectionandcorrectionandautomaticrepeatrequest(ARQ).
Avirtualcircuitisalinkbetweentwoormoreendstationsonapacket-switchedhashnetwork.Itprovidestemporaryordedicatedconnection-orientedsessionsbetweentwoendpoints.Itsinherentcharacteristicisthatthereisapredeterminedpaththroughthemultipathnetwork.Definingapathinadvancecanimproveperformanceandeliminatetheneedforheadersforframesandpackets,therebyincreasingthroughput.Fromatechnicalpointofview,thephysicalpathofthepacketswitchingnetworkcanbechangedtoavoidcongestionandfailureoftheline,butthetwoendsystemsmustmaintainaconnectionandchangethepathdescriptionasneeded.