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1、CHAPTER18MultiserviceAccessTechnologiesMultiservicenetworkingisemergingasastrategicallyimportantissueforenterpriseandpublicserviceproviderinfrastructuresalike.Thepropositionofmultiservicenetworkingisthecombinationofalltypesofcommunications,alltypesofdata,voice,andvideooverasinglepacket-cel
2、l-basedinfrastructure.Thebenefitsofmultiservicenetworkingarereducedoperationalcosts,higherperformance,greaterflexibility,integrationandcontrol,andfasternewapplicationandservicedeployment.AkeyissueoftenconfusedinmultiservicenetworkingisthedegreetowhichLayer2switchingandservicesaremixedwithLay
3、er3switchingandservices.Anintelligentmultiservicenetworkfullyintegratesboth,takingadvantageofthebestofeach;mostmultiserviceofferingsinthemarketplaceareprimarilyLayer2based,fromtraditionalcircuitswitchingtechnologysuppliers.TheImportanceofVoiceoverIPOfthekeyemergingtechnologiesfordata,voice
4、,andvideointegration,voiceoverIP(InternetProtocol)isarguablyveryimportant.Themostqualityofservice(QoS)sensitiveofalltraffic,voiceisthetruetestoftheengineeringandqualityofanetwork.DemandforVoiceoverIPisleadingthemovementforQoSinIPenvironments,andwillultimatelyleadtouseoftheInternetforfax,voi
5、cetelephony,andvideotelephonyservices.VoiceoverIPwillultimatelybeakeycomponentofthemigrationoftelephonytotheLANinfrastructure.SignificantadvancesintechnologyhavebeenmadeoverthepastfewyearsthatenablethetransmissionofvoicetrafficovertraditionalpublicnetworkssuchasFrameRelay(VoiceoverFrameRelay
6、)aswellasVoiceovertheInternetthroughtheeffortsoftheVoiceoverIPForumandtheInternetEngineeringTaskForce(IETF).Additionally,thesupportofAsynchronousTransferMode(ATM)fordifferenttraffictypesandtheATMForum’srecentcompletionoftheVoiceandTelephonyoverATMspecificationwillquickentheavailabilityofindu
7、stry-standardsolutions.PacketVoiceAllpacketvoicesystemsfollowacommonmodel,asshowninFigure18-1.Thepacketvoicetransportnetwork,whichmaybeIPbased,FrameRelay,orATM,formsthetraditional“cloud.”Attheedgesofthisnetworkaredevicesorcomponentsthatcanbecalledvoiceagents.I
