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1、Adaptive,Best-EffortDeliveryofDigitalAudioand*VideoAcrossPacket-SwitchedNetworksK.Jeffay,D.L.Stone,T.Talley,F.D.SmithUniversityofNorthCarolinaatChapelHillDepartmentofComputerScienceChapelHill,NC27599-3175USA{jeffay,stone,talley,smithfd}@cs.unc.eduAbstract:Wepre
2、sentanoverviewofa“best-effort”transportprotocolthatsupportsconferencingwithdigitalaudioandvideoacrossinterconnectedpacketswitchednetworks.Theprotocoldeliversthehighestqualityconferenceservicepossiblegiventhecurrentloadinthenetwork.Qualityisdefinedintermsofsynch
3、ronizationbetweenaudioandvideo,thenumberofframesplayedoutoforder,andtheend-to-endlatencyintheconference.Highqualityconferencearerealizedthroughfourtransportanddisplaymechanismsandareal-timeimplementationofthesemechanismsthatintegratesoperatingsystemservices(e.g
4、.,schedulingandresourceallocation,anddevicemanagement)withnetworkcommunicationservices(e.g.,transportprotocols).Inconcertthesemechanismsdynamicallyadapttheconferenceframeratetothebandwidthavailableinthenetwork,minimizethelatencyinthedisplayedstreamswhileavoidin
5、gdiscontinuities,andprovidequasi-reliabledeliveryofaudioframes.1.IntroductionThefocusofthisworkisonthereal-timetransmissionoflivedigitalaudioandvideoacrossinterconnectedpacket-switchednetworks.Ourgoalistosupporthigh-fidelityaudio/videoconferences,e.g.,conferenc
6、eswithhighqualityaudioandfull-motioncolorvideo.Theapproachoneadoptsforthereal-timecommunicationofaudioandvideowilldependonnumerousfactorsincludingthearchitectureoftheaudio/videosubsystem,theencodingandcompressiontechnologiesemployedintheaudio/videosubsystem,the
7、availablenetworkbandwidth,andthedegreeofphysicallayersupportinthenetworkforreal-timecommunication.Asastartingpointweconsiderexistinglocalareanetworks(i.e.,ethernets,tokenrings,andFDDIrings)interconnectedbybridgesorrouters,andanaudio/videosystemthatacquiresandco
8、mpressesindividualframesofvideoatNTSCrates.Onetechnicalchallengeinthisenvironmentistomanageandaccommodatejitterintheaudio/videostreamsseenbytheprocessesresponsiblefordisplay
