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外文文献原文OnthedeploymentofVoIPinEthernetnetworks:methodologyandcasestudyKhaledSalah,DepartmentofInformationandComputerScience,KingFahdUniversityofPetroleumandMinerals,P.O.Box5066,Dhahran31261,SaudiArabiaReceived25May2004;revised3June2005;accepted3June2005.Availableonline1July2005.AbstractDeployingIPtelephonyorvoiceoverIP(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，IIAnalysis，Simulation，OPNET1IntroductionThesedaysamassivedeploymentofVoIPistakingplaceoverdatanetworks.MostofthesenetworksareEthernetbasedandrunningIPprotocol.Manynetworkmanagersarefindingitveryattractiveandcosteffectivetomergeandunifyvoiceanddatanetworksintoone.Itiseasiertorun,manage,andmaintain.However,onehastokeepinmindthatIPnetworksarebest-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,impactofVoIPonexistingIIInetworkservicesandapplications,andimpactbackgroundtrafficonVoIP.ThispaperattemptstoaddressthoseimportantfactorsandlayoutacomprehensivemethodologyforasuccessfuldeploymentofanymultimediaapplicationsuchasVoIPandvideoconferencing.However,thepaperfocusesonVoIPasthenewserviceofinteresttobedeployed.Thepaperalsocontainsmanyusefulengineeringanddesignguidelines,anddiscussesmanypracticalissuespertainingtothedeploymentofVoIP.TheseissuesincludecharacteristicsofVoIPtrafficandQoSrequirements,VoIPflowandcalldistribution,definingfuturegrowthcapacity,andmeasurementandimpactofbackgroundtraffic.Asacasestudy,weillustratehowourapproachandguidelinescanbeappliedtoatypicalnetworkofasmallenterprise.Therestofthepaperisorganizedasfollows.Section2presentsatypicalnetworktopologyofasmallenterprisetobeusedasacasestudyfordeployingVoIP.Section3outlinespracticaleight-stepmethodologytodeploysuccessfullyVoIPindatanetworks.Eachstepisdescribedinconsiderabledetail.Section4describesimportantdesignandengineeringdecisionstobemadebasedontheanalyticandsimulationstudies.Section5concludesthestudyandidentifiesfuturework.IV2ExistingnetworkFig.1illustratesatypicalnetworktopologyforasmallenterpriseresidinginahigh-risebuilding.Thenetworkshownisrealisticandusedasacasestudyonly;however,ourworkpresentedinthispapercanbeadoptedeasilyforlargerandgeneralnetworksbyfollowingthesameprinciples,guidelines,andconceptslaidoutinthispaper.ThenetworkisEthernet-basedandhastwoLayer-2Ethernetswitchesconnectedbyarouter.TherouterisCisco2621,andtheswitchesare3ComSuperstack3300.Switch1connectsFloors1and2andtwose