英文文献_科技类_原文及翻译_(电子_电气_自动化_通信)1

外文文献原文OnthedeploymentofVoIPinEthernetnetworks:methodologyandcasestudyAbstractDeployingIPtelephonyorvoiceoverIP(VoIP)isamajorandchallengingtaskfordatanetworkresearchersanddesigners.Thispaperoutlinesguidelinesandastep-by-stepmethodologyonhowVoIPcanbedeployedsuccessfully.Themethodologycanbeusedtoassessthesupportandreadinessofanexistingnetwork.PriortothepurchaseanddeploymentofVoIPequipment,themethodologypredictsthenumberofVoIPcallsthatcanbesustainedbyanexistingnetworkwhilesatisfyingQoSrequirementsofallnetworkservicesandleavingadequatecapacityforfuturegrowth.Asacasestudy,weapplythemethodologystepsonatypicalnetworkofasmallenterprise.Weutilizebothanalysisandsimulationtoinvestigatethroughputanddelaybounds.Ouranalysisisbasedonqueuingtheory,andOPNETisusedforsimulation.Resultsobtainedfromanalysisandsimulationareinlineandgiveaclosematch.Inaddition,thepaperdiscussesmanydesignandengineeringissues.TheseissuesincludecharacteristicsofVoIPtrafficandQoSrequirements,VoIPflowandcalldistribution,definingfuturegrowthcapacity,andmeasurementandimpactofbackgroundtraffic.Keywords:NetworkDesign，NetworkManagement，VoIP，PerformanceEvaluation，Analysis，Simulation，OPNET1IntroductionThesedaysamassivedeploymentofVoIPistakingplaceoverdatanetworks.MostofthesenetworksareEthernetbasedandrunningIPprotocol.Manynetworkmanagersarefindingitveryattractiveandcosteffectivetomergeandunifyvoiceanddatanetworksintoone.Itiseasiertorun,manage,andmaintain.However,onehastokeepinmindthatIPIInetworksarebest-effortnetworksthatweredesignedfornon-realtimeapplications.Ontheotherhand,VoIPrequirestimelypacketdeliverywithlowlatency,jitter,packetloss,andsufficientbandwidth.Toachievethisgoal,anefficientdeploymentofVoIPmustensurethesereal-timetrafficrequirementscanbeguaranteedoverneworexistingIPnetworks.WhendeployinganewnetworkservicesuchasVoIPoverexistingnetwork,manynetworkarchitects,managers,planners,designers,andengineersarefacedwithcommonstrategic,andsometimeschallenging,questions.WhataretheQoSrequirementsforVoIP?HowwillthenewVoIPloadimpacttheQoSforcurrentlyrunningnetworkservicesandapplications?WillmyexistingnetworksupportVoIPandsatisfythestandardizedQoSrequirements?Ifso,howmanyVoIPcallscanthenetworksupportbeforeupgradingprematurelyanypartoftheexistingnetworkhardware?Thesechallengingquestionshaveledtothedevelopmentofsomecommercialtoolsfortestingtheperformanceofmultimediaapplicationsindatanetworks.AlistoftheavailablecommercialtoolsthatsupportVoIPislistedin[1,2].Forthemostpart,thesetoolsusetwocommonapproachesinassessingthedeploymentofVoIPintotheexistingnetwork.OneapproachisbasedonfirstperformingnetworkmeasurementsandthenpredictingthenetworkreadinessforsupportingVoIP.Thepredictionofthenetworkreadinessisbasedonassessingthehealthofnetworkelements.ThesecondapproachisbasedoninjectingrealVoIPtrafficintoexistingnetworkandmeasuringtheresultingdelay,jitter,andloss.Otherthanthecostassociatedwiththecommercialtools,noneofthecommercialtoolsofferacomprehensiveapproachforsuccessfulVoIPdeployment.Inparticular,nonegivesanypredictionforthetotalnumberofcallsthatcanbesupportedbythenetworktakingintoaccountimportantdesignandengineeringfactors.ThesefactorsincludeVoIPflowandcalldistribution,futuregrowthcapacity,performancethresholds,impactofVoIPonexistingnetworkservicesandapplications,andimpactbackgroundtrafficonVoIP.ThispaperattemptstoaddressthoseimportantfactorsandlayoutacomprehensivemethodologyforasuccessfuldeploymentofanymultimediaapplicationsuchasVoIPandvideoconferencing.However,thepaperfocusesonVoIPasthenewserviceofinteresttobedeployed.Thepaperalsocontainsmanyusefulengineeringanddesignguidelines,anddiscussesmanypracticalissuespertainingtothedeploymentofVoIP.TheseissuesincludecharacteristicsofVoIPIIItrafficandQoSrequirements,VoIPflowandcalldistribution,definingfuturegrowthcapacity,andmeasurementandimpactofbackgroundtraffic.Asacasestudy,weillustratehowourapproachandguidelinescanbeappliedtoatypicalnetworkofasmallenterprise.Therestofthepaperisorganizedasfollows.Section2presentsatypicalnetworktopologyofasmallenterprisetobeusedasacasestudyfordeployingVoIP.Section3outlinespracticaleight-stepmethodologytodeploysuccessfullyVoIPindatanetworks.Eachstepisdescribedinconsiderabledetail.Section4describesimportantdesignandengineeringdecisionstobemadebasedontheanalyticandsimulationstudies.Section5concludesthestudyandidentifiesfuturework.2ExistingnetworkIVFig.1illustratesatypicalnetworktopologyforasmallenterpriseresidinginahigh-risebuilding.Thenetworkshownisrealisticandusedasacasestudyonly;however,ourworkpresentedinthispapercanbeadoptedeasilyforlargerandgeneralnetworksbyfollowingthesameprinciples,guidelines,andconceptslaidoutinthispaper.ThenetworkisEthernet-basedandhastwoLayer-2Ethernetswitchesconnectedbyarouter.TherouterisCisco2621,andtheswitchesare3ComSuperstack3300.Switch1connectsFloors1and2andtwoservers;whileSwitch2connectsFloor3andfourservers.EachfloorLANisbasicallyasharedEthernetconnectingemployeePCswithworkgroupandprinterservers.ThenetworkmakesuseofVLANsinordertoisolatebroadcastandmulticasttraffic.At