英文文献科技类原文及翻译电子电气自动化通信1.docx
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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:
methodologyandcasestudy
Abstract
DeployingIPtelephonyorvoiceoverIP(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,OPNET
1Introduction
ThesedaysamassivedeploymentofVoIPistakingplaceoverdatanetworks.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,impactofVoIPonexistingnetworkservicesandapplications,andimpactbackgroundtrafficonVoIP.ThispaperattemptstoaddressthoseimportantfactorsandlayoutacomprehensivemethodologyforasuccessfuldeploymentofanymultimediaapplicationsuchasVoIPandvideoconferencing.However,thepaperfocusesonVoIPasthenewserviceofinteresttobedeployed.Thepaperalsocontainsmanyusefulengineeringanddesignguidelines,anddiscussesmanypracticalissuespertainingtothedeploymentofVoIP.TheseissuesincludecharacteristicsofVoIPtrafficandQoSrequirements,VoIPflowandcalldistribution,definingfuturegrowthcapacity,andmeasurementandimpactofbackgroundtraffic.Asacasestudy,weillustratehowourapproachandguidelinescanbeappliedtoatypicalnetworkofasmallenterprise.Therestofthepaperisorganizedasfollows.Section2presentsatypicalnetworktopologyofasmallenterprisetobeusedasacasestudyfordeployingVoIP.Section3outlinespracticaleight-stepmethodologytodeploysuccessfullyVoIPindatanetworks.Eachstepisdescribedinconsiderabledetail.Section4describesimportantdesignandengineeringd