第二章宽带业务特征与服务质量保证

[e-mail]2005-11-092™™Internet™Internet22005-11-093™2.1¾¾¾¾™2.2¾¾(QoS)¾2005-11-094™¾/(VoiceandAudio)¾/(ImageandVideo)¾(Data)™/¾(Signaling)¾(Control)¾(OAM)32005-11-095QoS™¾Delay-sensitive,butgenerallyloss-tolerable¾Voiceandvideo,andreal-timedata™¾Delay-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)¾Smallpacketsarepreferable¾Sometransmissionerrorsaretolerable52005-11-0993™WorldWideWeb()¾Asetofhyperlinkeddocuments(webpages)¾Eachwebpagemaycontaintext,pictures,audioclips,videoclips,andpossiblelinks¾Whenyoubrowsetheweb,youinitiateasequenceoffiletransfers¾Thesizeofawebpagetypicallyrangesfromafewkilobytestoafewmegabytes¾Weexpectwebpagetransferstobeerror-free¾Wealsodonotwantto“WorldWideWait”!2005-11-09102.2™¾¾¾¾™¾¾¾62005-11-0911™(delay-sensitive)¾¾™(loss-sensitive)¾¾™ATM(delay-and-losssensitive)¾DifferentiatedQoS2005-11-0912QualityofService:Whatisit?Multimediaapplications:networkaudioandvideonetworkprovidesapplicationwithlevelofperformanceneededforapplicationtofunction.QoS72005-11-0913QoS:isitreallynecessary?™No:¾QoSguaranteebytrafficcontrolandresourcemanagementistoocomplicatedtobepractical¾Over-provisionofbandwidthwillprovideQoS™Yes:¾Trafficgrowthisalwaysfasterthanbandwidthgrowth;overprovisioncannotsolvethecongestioncompletely¾Bandwidthavailablecannotbeinfinite,especiallyattheedge(includingwirelessaccess)¾QoScontrolshouldbeend-to-end,otherwiseyoujustmovetheproblemelsewhere¾SeamlesshandoverandroamingofmobilehostsneedstrictQoS¾QoSdifferentiationandtariffneedQoSguarantee(“Conceptswithoutintuitionsareempty;intuitionswithoutconceptsareblind”)2005-11-0914WhybetterthanBestEffort?™Tosupportawiderrangeofapplications¾Real-time,Multimedia,etc™Todevelopsustainableeconomicmodelsandnewprivatenetworkingservices¾Currentflatpricedmodels,andbest-effortservicesdonotcutitforbusinesses82005-11-0915What’sQoS?™ITUDefinition:“QoSisthecollectiveeffectofserviceperformancewhichdeterminethedegreeofsatisfactionofauseroftheservice”¾itisameasureofthesatisfactionexperiencedbyapersonwhilereceivingaservice¾itisauserperceptionanddifferentfromnetworkperformance(NP)!¾servicesupport,operability,servability,andsecurity™IETFDefinition:“Asetofservicerequirementstobemetbythenetworkwhiletransportingaflow”¾itiscloselyequivalenttothenotionofNP!(mucheasier!)¾itisameasureofnetworkperformanceratherthantheuserQoS2005-11-0916What’sQoS?™Technically,weusuallytransfertheQoSlevelintoNP(intrinsicQoS)parameters¾BitRate(bandwidth)¾BlockingProb.and/orPacketLossRate¾Delay(meanand/ormaximum)time,¾Jitter™Additionally,intrinsicQoSmayhavethefollowingattributes:¾end-to-end(e.g.,IntServ)orlimitedtoaparticulardomain(e.g.,DiffServ)¾appliedtoalltrafficorjusttoaparticularsession¾unidirectionalorbidirectional¾guaranteedorstatistical92005-11-0917VariousAspectsofQoS™QoSisnotonlyblocking/lossprob.,delay,anddelayvariation,butalso(fromusers’pointofview)¾Connectivity(e.g.,handoff)¾Flexibility¾Security™and(fromnetworkpointofview)¾Resourceutilizationratio¾Survivabilityorreliability(needredundancy!)™QoSdependsalsoon¾Diverseuserrequirements¾Heterogeneoususerperception¾Differentcompressionandcodingtechniques¾Pricingandchargingpolicy2005-11-0918TheGeneralQoSModelandITU/ETSI/IETFApproachesNetworkPerformanceQualityofServiceQoSperceivedbycustomersQoSrequirementsofthecustomerQoSachievedbytheprovidersQoSofferedbytheprovidersQoSGeneralModelAccessedQoSPerceivedQoSIntrinsicQoSITU/ETSIapproachIETFapproach102005-11-0919QoS:It’snotFree™QoSisnotonlybandwidth,butmoretrafficcontrolandmanagement¾Trafficcontrolandmanagementisnotcheap™QoSisnotonlyinthecore,butmoreontheedges¾End-endQoSisexpensive™CostofWirelessBandwidthC=NuserxBuserxxAservicexf(Q)WhereNuser=numberofusers;Buser=bandwidth/user;=bandwidthutilizationratioAservice=servicearea(coverage);f(Q)=QoSguaranteelevelf(Q)Q(SeamailvsEMS)2005-11-0920QoSforDifferentMedia™Voiceusersis¾Unpredictableuserdemands¾Unpredictablenetworkload¾Unpredictablepropagation™DatausersaregreedytotheirQoS¾Unpredictableuserdemands¾Unpredictablenetworkload¾Unpredictablepropagation¾Unpredictableavailablebitrate112005-11-0921QoSforWirelessData™Wirelessdatausershaveadditionalproblems:¾Unpredictableuserdemands¾Unpredictablenetworkload¾Unpredictablepropagation¾Unpredictablecompetitionforspectrumresource¾Unpredictab