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12005-11-091niuzhs@tsinghua.edu.cn2005-11-092InternetInternet22005-11-0932.1¾¾¾¾2.2¾¾(QoS)¾2005-11-094¾/(VoiceandAudio)¾/(ImageandVideo)¾(Data)/¾(Signaling)¾(Control)¾(OAM)32005-11-095QoS¾Delay-sensitive,butgenerallyloss-tolerable¾Voiceandvideo,andreal-timedata¾Delay-insensitive,butgenerallyloss-sensitive¾Non-real-timedata2005-11-096(CBR:ConstantBitRate)¾Voice,MPEG1,CircuitEmulation,……(VBR:VariableBitRate)¾Video,MPEG2,Data,……(ABR:AvailableBitRate)¾Data,VirtualLAN,……(UBR:UnspecificBitRate)¾Data,……42005-11-0971(AudioorVideoStreams)¾Onewaytransmission(e.g.,MP3orWebTV)¾Absorbthedelayfluctuationsbybufferingatreceiver¾Delayjitterismuchmoreserious,butfixeddelayisunimportant¾Transmissionraterangesfrom8Kbpsto30Kbps(audio)orfrom40Kbpsto80Kbps(video)¾Sometransmissionerrorsareacceptable(e.g.,BER10-4foruncompressedsignalorBER10-6forcompressedsignal)2005-11-0982(PacketizedVoiceandVideoconferences)¾Twowaycommunication(e.g.,VoIP)¾Sensitivetobothmaximumdelayanddelayjitter¾Transmissionrateis4-64Kbps(voice),8Kbps-1.3Mbps(CDqualityaudio),1.15-3Mbps(MPEG1),or4Mbps(MPEG2)¾Smallpacketsarepreferable¾Sometransmissionerrorsaretolerable52005-11-0993WorldWideWeb()¾Asetofhyperlinkeddocuments(webpages)¾Eachwebpagemaycontaintext,pictures,audioclips,videoclips,andpossiblelinks¾Whenyoubrowsetheweb,youinitiateasequenceoffiletransfers¾Thesizeofawebpagetypicallyrangesfromafewkilobytestoafewmegabytes¾Weexpectwebpagetransferstobeerror-free¾Wealsodonotwantto“WorldWideWait”!2005-11-09102.2¾¾¾¾¾¾¾62005-11-0911(delay-sensitive)¾¾(loss-sensitive)¾¾ATM(delay-and-losssensitive)¾DifferentiatedQoS2005-11-0912QualityofService:Whatisit?Multimediaapplications:networkaudioandvideonetworkprovidesapplicationwithlevelofperformanceneededforapplicationtofunction.QoS72005-11-0913QoS:isitreallynecessary?No:¾QoSguaranteebytrafficcontrolandresourcemanagementistoocomplicatedtobepractical¾Over-provisionofbandwidthwillprovideQoSYes:¾Trafficgrowthisalwaysfasterthanbandwidthgrowth;overprovisioncannotsolvethecongestioncompletely¾Bandwidthavailablecannotbeinfinite,especiallyattheedge(includingwirelessaccess)¾QoScontrolshouldbeend-to-end,otherwiseyoujustmovetheproblemelsewhere¾SeamlesshandoverandroamingofmobilehostsneedstrictQoS¾QoSdifferentiationandtariffneedQoSguarantee(“Conceptswithoutintuitionsareempty;intuitionswithoutconceptsareblind”)2005-11-0914WhybetterthanBestEffort?Tosupportawiderrangeofapplications¾Real-time,Multimedia,etcTodevelopsustainableeconomicmodelsandnewprivatenetworkingservices¾Currentflatpricedmodels,andbest-effortservicesdonotcutitforbusinesses82005-11-0915What’sQoS?ITUDefinition:“QoSisthecollectiveeffectofserviceperformancewhichdeterminethedegreeofsatisfactionofauseroftheservice”¾itisameasureofthesatisfactionexperiencedbyapersonwhilereceivingaservice¾itisauserperceptionanddifferentfromnetworkperformance(NP)!¾servicesupport,operability,servability,andsecurityIETFDefinition:“Asetofservicerequirementstobemetbythenetworkwhiletransportingaflow”¾itiscloselyequivalenttothenotionofNP!(mucheasier!)¾itisameasureofnetworkperformanceratherthantheuserQoS2005-11-0916What’sQoS?Technically,weusuallytransfertheQoSlevelintoNP(intrinsicQoS)parameters¾BitRate(bandwidth)¾BlockingProb.and/orPacketLossRate¾Delay(meanand/ormaximum)time,¾JitterAdditionally,intrinsicQoSmayhavethefollowingattributes:¾end-to-end(e.g.,IntServ)orlimitedtoaparticulardomain(e.g.,DiffServ)¾appliedtoalltrafficorjusttoaparticularsession¾unidirectionalorbidirectional¾guaranteedorstatistical92005-11-0917VariousAspectsofQoSQoSisnotonlyblocking/lossprob.,delay,anddelayvariation,butalso(fromusers’pointofview)¾Connectivity(e.g.,handoff)¾Flexibility¾Securityand(fromnetworkpointofview)¾Resourceutilizationratio¾Survivabilityorreliability(needredundancy!)QoSdependsalsoon¾Diverseuserrequirements¾Heterogeneoususerperception¾Differentcompressionandcodingtechniques¾Pricingandchargingpolicy2005-11-0918TheGeneralQoSModelandITU/ETSI/IETFApproachesNetworkPerformanceQualityofServiceQoSperceivedbycustomersQoSrequirementsofthecustomerQoSachievedbytheprovidersQoSofferedbytheprovidersQoSGeneralModelAccessedQoSPerceivedQoSIntrinsicQoSITU/ETSIapproachIETFapproach102005-11-0919QoS:It’snotFreeQoSisnotonlybandwidth,butmoretrafficcontrolandmanagement¾TrafficcontrolandmanagementisnotcheapQoSisnotonlyinthecore,butmoreontheedges¾End-endQoSisexpensiveCostofWirelessBandwidthC=NuserxBuserxxAservicexf(Q)WhereNuser=numberofusers;Buser=bandwidth/user;=bandwidthutilizationratioAservice=servicearea(coverage);f(Q)=QoSguaranteelevelf(Q)Q(SeamailvsEMS)2005-11-0920QoSforDifferentMediaVoiceusersis¾Unpredictableuserdemands¾Unpredictablenetworkload¾UnpredictablepropagationDatausersaregreedytotheirQoS¾Unpredictableuserdemands¾Unpredictablenetworkload¾Unpredictablepropagation¾Unpredictableavailablebitrate112005-11-0921QoSforWirelessDataWirelessdatausershaveadditionalproblems:¾Unpredictableuserdemands¾Unpredictablenetworkload¾Unpredictablepropagation¾Unpredictablecompetitionforspectrumresource¾Unpredictab