計(jì)算機(jī)網(wǎng)絡(luò)-Chapter-9-V7.0-課件

ComputerNetworking:ATopDownApproach

AnoteontheuseofthesePowerpointslides:We’remakingtheseslidesfreelyavailabletoall(faculty,students,readers).They’reinPowerPointformsoyouseetheanimations;andcanadd,modify,anddeleteslides(includingthisone)andslidecontenttosuityourneeds.Theyobviouslyrepresentalotofworkonourpart.Inreturnforuse,weonlyaskthefollowing:Ifyouusetheseslides(e.g.,inaclass)thatyoumentiontheirsource(afterall,we’dlikepeopletouseourbook!)Ifyoupostanyslidesonawwwsite,thatyounotethattheyareadaptedfrom(orperhapsidenticalto)ourslides,andnoteourcopyrightofthismaterial.Thanksandenjoy!JFK/KWRAllmaterialcopyright1996-2016J.FKuroseandK.W.Ross,AllRightsReserved7thedition

JimKurose,KeithRoss

Pearson/AddisonWesley

April2016Chapter9

MultimediaNetworking9-1MultimediaNetworkingComputerNetworking:ATopDowMultimedianetworking:outline9.1

multimedianetworkingapplications9.2streamingstoredvideo9.3

voice-over-IP9.4protocolsforreal-timeconversational

applications9.5networksupportformultimedia9-2MultimediaNetworkingMultimedianetworking:outlineMultimedia:audioanalogaudiosignalsampledatconstantratetelephone:8,000samples/secCDmusic:44,100samples/seceachsamplequantized,i.e.,roundede.g.,28=256possiblequantizedvalueseachquantizedvaluerepresentedbybits,e.g.,8bitsfor256valuestimeaudiosignalamplitudeanalogsignalquantizedvalueofanalogvaluequantizationerrorsamplingrate(Nsample/sec)9-3MultimediaNetworkingMultimedia:audioanalogaudioMultimedia:audioexample:8,000samples/sec,256quantizedvalues:64,000bpsreceiverconvertsbitsbacktoanalogsignal:somequalityreductionexampleratesCD:1.411MbpsMP3:96,128,160kbpsInternettelephony:5.3kbpsanduptimeaudiosignalamplitudeanalogsignalquantizedvalueofanalogvaluequantizationerrorsamplingrate(Nsample/sec)9-4MultimediaNetworkingMultimedia:audioexample:8,00video:sequenceofimagesdisplayedatconstantratee.g.,24images/secdigitalimage:arrayofpixelseachpixelrepresentedbybitscoding:useredundancywithinandbetween

imagestodecrease#bitsusedtoencodeimagespatial(withinimage)temporal(fromoneimagetonext)Multimedia:video……...…spatialcodingexample:insteadofsendingNvaluesofsamecolor(allpurple),sendonlytwovalues:colorvalue(purple)andnumberofrepeatedvalues(N)……...…frameiframei+1temporalcodingexample:insteadofsendingcompleteframeati+1,sendonlydifferencesfromframei9-5MultimediaNetworkingvideo:sequenceofimagesdispMultimedia:video……...…spatialcodingexample:insteadofsendingNvaluesofsamecolor(allpurple),sendonlytwovalues:colorvalue(purple)andnumberofrepeatedvalues(N)……...…frameiframei+1temporalcodingexample:insteadofsendingcompleteframeati+1,sendonlydifferencesfromframeiCBR:(constantbitrate):videoencodingratefixedVBR:(variablebitrate):videoencodingratechangesasamountofspatial,temporalcodingchangesexamples:MPEG1(CD-ROM)1.5MbpsMPEG2(DVD)3-6MbpsMPEG4(oftenusedinInternet,<1Mbps)9-6MultimediaNetworkingMultimedia:video……...…sMultimedianetworking:3applicationtypesstreaming,stored

audio,videostreaming:canbeginplayoutbeforedownloadingentirefilestored(atserver):cantransmitfasterthanaudio/videowillberendered(impliesstoring/bufferingatclient)e.g.,YouTube,Netflix,Huluconversationalvoice/videooverIPinteractivenatureofhuman-to-humanconversationlimitsdelaytolerancee.g.,Skypestreamingliveaudio,videoe.g.,livesportingevent(futbol)9-7MultimediaNetworkingMultimedianetworking:3appliMultimedianetworking:outline9.1

multimedianetworkingapplications9.2streamingstoredvideo9.3

voice-over-IP9.4protocolsforreal-timeconversational

applications9.5networksupportformultimedia9-8MultimediaNetworkingMultimedianetworking:outlineStreamingstoredvideo:videorecorded(e.g.,30frames/sec)2.videosentCumulativedatastreaming:atthistime,clientplayingoutearlypartofvideo,whileserverstillsendinglaterpartofvideonetworkdelay(fixedinthisexample)time3.videoreceived,playedoutatclient(30frames/sec)9-9MultimediaNetworkingStreamingstoredvideo:video2Streamingstoredvideo:challengescontinuousplayoutconstraint:onceclientplayoutbegins,playbackmustmatchoriginaltiming…butnetworkdelaysarevariable(jitter),sowillneedclient-sidebuffertomatchplayoutrequirementsotherchallenges:clientinteractivity:pause,fast-forward,rewind,jumpthroughvideovideopacketsmaybelost,retransmitted9-10MultimediaNetworkingStreamingstoredvideo:challeconstantbitratevideotransmissionCumulativedatatimevariablenetworkdelayclientvideoreceptionconstantbitratevideoplayoutatclientclientplayoutdelaybufferedvideoclient-sidebuffering

andplayoutdelay:compensatefornetwork-addeddelay,delayjitterStreamingstoredvideo:revisited9-11MultimediaNetworkingconstantbitCumulativeClient-sidebuffering,playoutvariablefillrate,x(t)clientapplicationbuffer,sizeBplayoutrate,e.g.,CBRrbufferfilllevel,Q(t)videoserverclient9-12MultimediaNetworkingClient-sidebuffering,playoutClient-sidebuffering,playoutvariablefillrate,x(t)clientapplicationbuffer,sizeBplayoutrate,e.g.,CBRrbufferfilllevel,Q(t)videoserverclient1.Initialfillofbufferuntilplayoutbeginsattp2.playoutbeginsattp,3.bufferfilllevelvariesovertimeasfillrate

x(t)variesandplayoutraterisconstant9-13MultimediaNetworkingClient-sidebuffering,playoutplayoutbuffering:averagefillrate(x),playoutrate(r):x<r:buffereventuallyempties(causingfreezingofvideoplayoutuntilbufferagainfills)x>r:bufferwillnotempty,providedinitialplayoutdelayislargeenoughtoabsorbvariabilityinx(t)initialplayoutdelaytradeoff:bufferstarvationlesslikelywithlargerdelay,butlargerdelayuntiluserbeginswatchingvariablefillrate,x(t)clientapplicationbuffer,sizeBplayoutrate,e.g.,CBRrbufferfilllevel,Q(t)videoserverClient-sidebuffering,playout9-14MultimediaNetworkingplayoutbuffering:averagefilStreamingmultimedia:UDPserversendsatrateappropriateforclientoften:sendrate=encodingrate=constantratetransmissionratecanbeoblivioustocongestionlevelsshortplayoutdelay(2-5seconds)toremovenetworkjittererrorrecovery:application-level,timepermittingRTP[RFC2326]:multimediapayloadtypesUDPmaynotgothroughfirewalls9-15MultimediaNetworkingStreamingmultimedia:UDPserveStreamingmultimedia:HTTPmultimediafileretrievedviaHTTPGETsendatmaximumpossiblerateunderTCPfillratefluctuatesduetoTCPcongestioncontrol,retransmissions(in-orderdelivery)largerplayoutdelay:smoothTCPdeliveryrateHTTP/TCPpassesmoreeasilythroughfirewallsvariablerate,x(t)TCPsendbuffervideofileTCPreceivebufferapplicationplayoutbufferserverclient9-16MultimediaNetworkingStreamingmultimedia:HTTPmultMultimedianetworking:outline9.1

multimedianetworkingapplications9.2streamingstoredvideo9.3voice-over-IP9.4protocolsforreal-timeconversational

applications9.5networksupportformultimedia9-17MultimediaNetworkingMultimedianetworking:outlineVoice-over-IP(VoIP)VoIPend-end-delayrequirement:neededtomaintain“conversational”aspecthigherdelaysnoticeable,impairinteractivity<150msec:good>400msecbadincludesapplication-level(packetization,playout),networkdelayssessioninitialization:howdoescalleeadvertiseIPaddress,portnumber,encodingalgorithms?value-addedservices:callforwarding,screening,recordingemergencyservices:9119-18MultimediaNetworkingVoice-over-IP(VoIP)VoIPend-eVoIP

characteristicsspeaker’saudio:alternatingtalkspurts,silentperiods.64kbpsduringtalkspurtpktsgeneratedonlyduringtalkspurts20msecchunksat8Kbytes/sec:160bytesofdataapplication-layerheaderaddedtoeachchunkchunk+headerencapsulatedintoUDPorTCPsegmentapplicationsendssegmentintosocketevery20msecduringtalkspurt9-19MultimediaNetworkingVoIPcharacteristicsspeaker’sVoIP:packetloss,delaynetworkloss:IPdatagramlostduetonetworkcongestion(routerbufferoverflow)delayloss:IPdatagramarrivestoolateforplayoutatreceiverdelays:processing,queueinginnetwork;end-system(sender,receiver)delaystypicalmaximumtolerabledelay:400mslosstolerance:dependingonvoiceencoding,lossconcealment,packetlossratesbetween1%and10%canbetolerated9-20MultimediaNetworkingVoIP:packetloss,delaynetworconstantbitratetransmissionCumulativedatatimevariablenetworkdelay(jitter)clientreception

constantbitrateplayoutatclientclientplayoutdelaybuffereddataDelayjitterend-to-enddelaysoftwoconsecutivepackets:differencecanbemoreorlessthan20msec(transmissiontimedifference)9-21MultimediaNetworkingconstantbitCumulativeVoIP:fixedplayoutdelayreceiverattemptstoplayouteachchunkexactlyqmsecsafterchunkwasgenerated.chunkhastimestampt:playoutchunkatt+q

chunkarrivesaftert+q:dataarrivestoolateforplayout:data“l(fā)ost”tradeoffinchoosingq:largeq:lesspacketlosssmallq:

betterinteractiveexperience9-22MultimediaNetworkingVoIP:fixedplayoutdelayreceisendergeneratespacketsevery20msecduringtalkspurt.firstpacketreceivedattimerfirstplayoutschedule:beginsatpsecondplayoutschedule:beginsatp’VoIP:fixedplayoutdelay9-23MultimediaNetworkingsendergeneratespacketseverAdaptiveplayoutdelay(1)goal:lowplayoutdelay,lowlatelossrateapproach:adaptiveplayoutdelayadjustment:estimatenetworkdelay,adjustplayoutdelayatbeginningofeachtalkspurtsilentperiodscompressedandelongatedchunksstillplayedoutevery20msecduringtalkspurtadaptivelyestimatepacketdelay:(EWMA-exponentiallyweightedmovingaverage,recallTCPRTTestimate):di=(1-a)di-1+a(ri–ti)delayestimateafterithpacketsmallconstant,e.g.0.1timereceived-timesent(timestamp)measureddelayofithpacket9-24MultimediaNetworkingAdaptiveplayoutdelay(1)goalalsousefultoestimateaveragedeviationofdelay,vi

:estimatesdi,vi

calculatedforeveryreceivedpacket,butusedonlyatstartoftalkspurtforfirstpacketintalkspurt,playouttimeis:remainingpacketsintalkspurtareplayedoutperiodicallyvi=(1-b)vi-1+b|ri–ti–di|playout-timei=ti+di+Kvi

Adaptiveplayoutdelay(2)9-25MultimediaNetworkingalsousefultoestimateaveragQ:

Howdoesreceiverdeterminewhetherpacketisfirstinatalkspurt?ifnoloss,receiverlooksatsuccessivetimestampsdifferenceofsuccessivestamps>20msec-->talkspurtbegins.withlosspossible,receivermustlookatbothtimestampsandsequencenumbersdifferenceofsuccessivestamps>20msecand

sequencenumberswithoutgaps-->talkspurtbegins.Adaptiveplayoutdelay(3)9-26MultimediaNetworkingQ:HowdoesreceiverdetermineVoiP:recoveryfrompacketloss(1)Challenge:recoverfrompacketlossgivensmalltolerabledelaybetweenoriginaltransmissionandplayouteachACK/NAKtakes~oneRTTalternative:ForwardErrorCorrection(FEC)sendenoughbitstoallowrecoverywithoutretransmission(recalltwo-dimensionalparityinCh.5)simpleFECforeverygroupofnchunks,createredundantchunkbyexclusiveOR-ingnoriginalchunkssendn+1chunks,increasingbandwidthbyfactor1/ncanreconstructoriginalnchunksifatmostonelostchunkfromn+1chunks,withplayoutdelay9-27MultimediaNetworkingVoiP:recoveryfrompacketlosanotherFECscheme:“piggybacklower

qualitystream”

sendlowerresolution

audiostreamas

redundantinformatione.g.,nominal

streamPCMat64kbps

andredundantstream

GSMat13kbpsnon-consecutiveloss:receivercanconceallossgeneralization:canalsoappend(n-1)stand(n-2)ndlow-bitrate

chunkVoiP:recoveryfrompacketloss(2)9-28MultimediaNetworkinganotherFECscheme:non-consecuinterleavingtoconcealloss:audiochunksdividedintosmallerunits,e.g.four5msecunitsper20msecaudiochunkpacketcontainssmallunitsfromdifferentchunksifpacketlost,stillhavemostofeveryoriginalchunknoredundancyoverhead,butincreasesplayoutdelayVoiP:recoveryfrompacketloss(3)9-29MultimediaNetworkinginterleavingtoconcealloss:isupernodeoverlaynetworkVoice-over-IP:Skypeproprietaryapplication-layerprotocol(inferredviareverseengineering)encryptedmsgsP2Pcomponents:Skypeclients(SC)clients:SkypepeersconnectdirectlytoeachotherforVoIPcallsupernodes(SN):

Skypepeerswithspecialfunctionsoverlaynetwork:amongSNstolocateSCsloginserverSkypeloginserversupernode(SN)9-30MultimediaNetworkingsupernodeVoice-over-IP:SkypeP2Pvoice-over-IP:SkypeSkypeclientoperation:1.joinsSkypenetworkbycontactingSN(IPaddresscached)usingTCP2.logs-in(username,password)tocentralizedSkypeloginserver3.obtainsIPaddressforcalleefromSN,SNoverlayorclientbuddylist4.initiatecalldirectlytocalleeSkypeloginserver9-31MultimediaNetworkingP2Pvoice-over-IP:SkypeSkypeproblem:bothAlice,Bobarebehind“NATs”

NATpreventsoutsidepeerfrominitiatingconnectiontoinsiderpeerinsidepeercaninitiateconnectiontooutsiderelaysolution:Alice,BobmaintainopenconnectiontotheirSNsAlicesignalsherSNtoconnecttoBobAlice’sSNconnectstoBob’sSNBob’sSNconnectstoBoboveropenconnectionBobinitiallyinitiatedtohisSNSkype:peersasrelays9-32MultimediaNetworkingproblem:bothAlice,BobarebMultimedianetworking:outline9.1

multimedianetworkingapplications9.2streamingstoredvideo9.3

voice-over-IP9.4protocolsforreal-timeconversational

applications:RTP,SIP9.5networksupportformultimedia9-33MultimediaNetworkingMultimedianetworking:outlineReal-TimeProtocol(RTP)RTPspecifiespacketstructureforpacketscarryingaudio,videodataRFC3550RTPpacketprovidespayloadtypeidentificationpacketsequencenumberingtimestampingRTPrunsinendsystemsRTPpacketsencapsulatedinUDPsegmentsinteroperability:iftwoVoIPapplicationsrunRTP,theymaybeabletoworktogether9-34MultimediaNetworkingReal-TimeProtocol(RTP)RTPspRTPrunsontopofUDPRTPlibrariesprovidetransport-layerinterfacethatextendsUDP:portnumbers,IPaddressespayloadtypeidentificationpacketsequencenumberingtime-stamping9-35MultimediaNetworkingRTPrunsontopofUDPRTPlibrRTPexampleexample:sending64kbpsPCM-encodedvoiceoverRTPapplicationcollectsencodeddatainchunks,e.g.,every20msec=160bytesinachunkaudiochunk+RTPheaderformRTPpacket,whichisencapsulatedinUDPsegmentRTPheaderindicatestypeofaudioencodingineachpacketsendercanchangeencodingduringconferenceRTPheaderalsocontainssequencenumbers,timestamps9-36MultimediaNetworkingRTPexampleexample:sending64RTPandQoSRTPdoesnotprovideanymechanismtoensuretimelydatadeliveryorotherQoSguaranteesRTPencapsulationonlyseenatendsystems(not

byintermediaterouters)routersprovidebest-effortservice,makingnospecialefforttoensurethatRTPpacketsarriveatdestinationintimelymatter9-37MultimediaNetworkingRTPandQoSRTPdoesnotprovidRTPheaderpayloadtype(7bits):indicatestypeofencodingcurrentlybeing

used.Ifsenderchangesencodingduringcall,senderinformsreceiverviapayloadtypefieldPayloadtype0:PCMmu-law,64kbpsPayloadtype3:GSM,13kbpsPayloadtype7:LPC,2.4kbpsPayloadtype26:MotionJPEGPayloadtype31:H.261Payloadtype33:MPEG2videosequence#(16bits):incrementbyoneforeachRTPpacketsentdetectpacketloss,restorepacketsequencepayloadtypesequencenumbertypetimestampSynchronizationSourceIDMiscellaneousfields9-38MultimediaNetworkingRTPheaderpayloadtype(7bitstimestampfield(32bitslong):

samplinginstantoffirstbyteinthisRTPdatapacketforaudio,timestampclockincrementsbyoneforeachsamplingperiod(e.g.,each125usecsfor8KHzsamplingclock)ifapplicationgenerateschunksof160encodedsamples,timestampincreasesby160foreachRTPpacketwhensourceisactive.Timestampclockcontinuestoincreaseatconstantratewhensourceisinactive.

SSRCfield(32bitslong):

identifiessourceof

RTPstream.EachstreaminRTPsessionhasdistinctSSRCRTPheaderpayloadtypesequencenumbertypetimestampSynchronizationSourceIDMiscellaneousfields9-39MultimediaNetworkingtimestampfield(32bitslong)RTSP/RTPprogrammingassignmentbuildaserverthatencapsulatesstoredvideoframesintoRTPpacketsgrabvideoframe,addRTPheaders,createUDPsegments,sendsegmentstoUDPsocketincludeseqnumbersandtimestampsclientRTPprovidedforyoualsowriteclientsideofRTSPissueplay/pausecommandsserverRTSPprovidedforyou9-40MultimediaNetworkingRTSP/RTPprogrammingassignmenReal-TimeControlProtocol(RTCP)worksinconjunctionwithRTPeachparticipantinRTPsessionperiodicallysendsRTCPcontrolpacketstoallotherparticipantseachRTCPpacketcontainssenderand/orreceiverreportsreportstatisticsusefultoapplication:#packetssent,#packetslost,interarrivaljitterfeedbackusedtocontrolperformancesendermaymodifyitstransmissionsbasedonfeedback9-41MultimediaNetworkingReal-TimeControlProtocol(RTRTCP:multiplemulticastsenderseachRTPsession:typicallyasinglemulticastaddress;allRTP/RTCPpacketsbelongingtosessionusemulticastaddressRTP,RTCPpacketsdistinguishedfromeachotherviadistinctportnumberstolimittraffic,eachparticipantreducesRTCPtrafficasnumberofconferenceparticipantsincreasesRTCPRTPRTCPRTCPsenderreceivers9-42MultimediaNetworkingRTCP:multiplemulticastsendeRTCP:packettypesreceiverreportpackets:fractionofpacketslost,lastsequencenumber,averageinterarrivaljittersenderreportpackets:SSRCofRTPstream,currenttime,numberofpacketssent,numberofbytessentsourcedescriptionpackets:e-mailaddressofsender,sender'sname,SSRCofassociatedRTPstreamprovidemappingbetweentheSSRCandtheuser/hostname9-43MultimediaNetworkingRTCP:packettypesreceiverrepRTCP:streamsynchronizationRTCPcansynchronizedifferentmediastreamswithinaRTPsessione.g.,videoconferencingapp:eachsendergeneratesoneRTPstreamforvideo,oneforaudio.timestampsinRTPpacketstiedtothevideo,audiosamplingclocksnottiedtowall-clocktimeeachRTCPsender-reportpacketcontains(formostrecentlygeneratedpacketinassociatedRTPstream):timestampofRTPpacketwall-clocktimeforwhenpacketwascreatedreceiversusesassociationtosynchronizeplayoutofaudio,video9-44MultimediaNetworkingRTCP:streamsynchronizationRTRTCP:bandwidthscalingRTCPattemptstolimititstrafficto5%ofsessionbandwidthexample:onesender,sendingvideoat2MbpsRTCPattemptstolimitRTCPtrafficto100KbpsRTCPgives75%ofratetoreceivers;remaining25%tosender75kbpsisequallysharedamongreceivers:withRreceivers,eachreceivergetstosendRTCPtrafficat75/Rkbps.sendergetstosendRTCPtrafficat25kbps.

participantdeterminesRTCPpackettransmissionperiodbycalculatingavgRTCPpacketsize(acrossentiresession)anddividingbyallocatedrate

9-45MultimediaNetworkingRTCP:bandwidthscalingRTCPatSIP:SessionInitiationProtocol

[RFC3261]long-termvision:alltelephonecalls,videoconferencecallstakeplaceoverInternetpeopleidentifiedbynamesore-mailaddresses,ratherthanbyphonenumberscanreachcallee(ifcalleesodesires),nomatterwherecalleeroams,nomatterwhatIPdevicecalleeiscurrentlyusing9-46MultimediaNetworkingSIP:SessionInitiationProtocSIPservicesSIPprovidesmechanismsforcallsetup:forcallertoletcalleeknowshewantstoestablishacallsocaller,calleecanagreeonmediatype,encodingtoendcalldeterminecurrentIPaddressofcallee:mapsmnemonicidentifiertocurrentIPaddresscallmanagement:addnewmediastreamsduringcallchangeencodingduringcallinviteotherstransfer,holdcalls9-47MultimediaNetworkingSIPservicesSIPprovidesmechaExample:settingupcalltoknownIPaddressAlice’sSIPinvitemessageindicatesherportnumber,IPaddress,encodingshepreferstoreceive(PCMmlaw)Bob’s200OKmessageindicateshisportnumber,IPaddress,preferredencoding(GSM)SIPmessagescanbesentoverTCPorUDP;heresentoverRTP/UDPdefaultSIPportnumberis50609-48MultimediaNetworkingExample:settingupcalltoknSettingupacall(more)codecnegotiation:supposeBobdoesn’thavePCMmlawencoderBobwillinsteadreplywith606NotAcceptableReply,listinghisencoders.AlicecanthensendnewINVITEmessage,advertisingdifferentencoderrejectingacallBobcanrejectwithreplies“busy,”

“gone,”

“paymentrequired,”

“forbidden”mediacanbesentoverRTPorsomeotherprotocol9-49MultimediaNetworkingSettingupacall(more)codecExampleofSIPmessageINVITEsip:bob@SIP/2.0Via:SIP/2.0/UDP4From:sip:alice@To:sip:bob@Call-ID:a2e3a@Content-Type:application/sdpContent-Length:885c=INIP44m=audio38060RTP/AVP0Notes:HTTPmessagesyntaxsdp=sessiondescriptionprotocolCall-IDisuniqueforeverycallHerewedon’tknowBob’sIPaddressintermediateSIP

serversneededAlicesends,receivesSIPmessagesusingSIPdefaultport506AlicespecifiesinheaderthatSIPclientsends,receivesSIPmessagesoverUDP9-50MultimediaNetworkingExampleofSIPmessageINVITEsNametranslation,userlocationcallerwantstocallcallee,butonlyhascallee’snameore-mailaddress.needtogetIPaddressofcallee’scurrenthost:usermovesaroundDHCPprotocoluserhasdifferentIPdevices(PC,smartphone,cardevice)resultcanbebasedon:timeofday(work,home)caller(don’twantbosstocallyouathome)statusofcallee(callssenttovoicemailwhencalleeisalreadytalkingtosomeone)9-51MultimediaNetworkingNametranslation,userlocatioSIPregistrarREGISTERsip:SIP/2.0Via:SIP/2.0/UDP9From:sip:bob@To:sip:bob@Expires:3600onefunctionofSIPserver:registrarwhenBobstartsSIPclient,clientsendsSIPREGISTERmessagetoBob’sregistrarserverregistermessage:9-52MultimediaNetworkingSIPregistrarREGISTERsip:domaSIPproxyanotherfunctionofSIPserver:proxyAlicesendsinvitemessagetoherproxyservercontainsaddresssip:bob@proxyresponsibleforroutingSIPmessagestocallee,possiblythroughmultipleproxiesBobsendsresponsebackthroughsamesetofSIPproxiesproxyreturnsBob’sSIPresponsemessagetoAlicecontainsBob’sIPaddressSIPproxyanalogoustolocalDNSserverplusTCPsetup9-53MultimediaNetworkingSIPproxyanotherfunctionofSSIPexample:jim@callskeith@11.JimsendsINVITE

messagetoUMassSIPproxy.2.UMassproxyforwardsrequesttoPolyregistrarserver23.Polyserverreturnsredirectresponse,

indicatingthatitshouldtrykeith@eurecom.fr35.eurecomregistrarforwardsINVITEto1,whichisrunningkeith’sSIPclient544.UmassproxyforwardsrequesttoEurecomregistrarserver8676-8.SIPresponsereturnedtoJim99.DataflowsbetweenclientsUMassSIPproxyPolySIPregistrarEurecomSIPregistrar1869-54MultimediaNetworkingSIPexample:jim@calComparisonwithH.323H.323:anothersignalingprotocolforreal-time,interactivemultimediaH.323:complete,verticallyintegratedsuiteofprotocolsformultimediaconferencing:signaling,registration,admissioncontrol,transport,codecsSIP:singlecomponent.WorkswithRTP,butdoesnotmandateit.Canbecombinedwithotherprotocols,servicesH.323comesfromtheITU(telephony)SIPcomesfromIETF:borrowsmuchofitsconceptsfromHTTPSIPhasWebflavor;H.323hastelephonyflavorSIPusesKISSprinciple:KeepItSimpleStupid9-55MultimediaNetworkingComparisonwithH.323H.323:anMultimedianetworking:outline9.1

multimedianetworkingapplications9.2streamingstoredvideo9.3

voice-over-IP9.4protocolsforreal-timeconversational

applications9.5networksupportformultimedia9-56MultimediaNetworkingMultimedianetworking:outlineNetworksupportformultimedia9-57MultimediaNetworkingNetworksupportformultimediaDimensioningbesteffortnetworksapproach:deployenoughlinkcapacitysothatcongestiondoesn’toccur,multimediatrafficflowswithoutdelayorlosslowcomplexityofnetworkmechanisms(usecurrent“besteffort”network)highbandwidthcostschallenges:networkdimensioning:howmuchbandwidthis“enough?”estimatingnetworktrafficdemand:neededtodeterminehowmuchbandwidthis“enough”(forthatmuchtraffic)9-58MultimediaNetworkingDimensioningbesteffortnetwoProvidingmultipleclassesofservicethusfar:makingthebestofbesteffortserviceone-sizefitsallservicemodelalternative:multipleclassesofservicepartitiontrafficintoclassesnetworktreatsdifferentclassesoftrafficdifferently(analogy:VIPserviceversusregularservice)0111granularity:differentialserviceamongmultipleclasses,notamongindividualconnectionshistory:ToSbits9-59MultimediaNetworkingProvidingmultipleclassesofMultipleclassesofservice:scenarioR1R2H1H2H3H41.5MbpslinkR1outputinterfacequeue9-60MultimediaNetworkingMultipleclassesofservice:sScenario1:mixedHTTPand