PowerPoint PresentationMultimedia ApplicationsClasses of Multimedia ApplicationsStreaming Stored Audio and VideoStreaming Live Audio and VideoReal-Time Interactive Audio and VideoDelay JitterMultimedia Over Today’s InternetHow Should the Internet Evolve to Better Support Multimedia?Quality of Service in the InternetThe slides of part 1-3 are adapted from the slides of chapter 7 published at the companion website of the book: Computer Networking : A Top-Down Approach Featuring the Internet, James F. Kurose, Keith W. Ross, Addison-Wesley, 3rd edition, 2004.Multimedia Applications Multimedia applications: transmit and receive audio and video over the Internet (e.g. streaming video, IP telephony, Internet radio, teleconferencing)Fundamental characteristics:delay sensitiveloss tolerant: infrequent losses cause minor glitches Different from elastic applications (e.g., file transfer, Web, email, telnet), which are loss intolerant and delay tolerantClasses of Multimedia Applications Streaming stored audio and videoStreaming live audio and videoReal-time interactive audio and videoStreaming Stored Audio and VideoPrerecorded media stored on servers, media transmitted to client on demandExamples: audio of a lecture, archives of radio broadcasts, movies, MTV clipsStreaming: client playout begins before all data has arrivedbuffer needed at clientDelay constraint: data must be received in time for playout at the clientInteractivity: client can pause, rewind, fast-forward1-2 sec until command effect OKStreaming Live Audio and VideoExamples: Internet radio talk show, live sporting eventStreamingplayback buffer at clientplayback can lag tens of seconds after requestdelay constraint: data must be received in time for playout at the clientInteractivityNot stored fast forward impossiblerewind, pause possible with local storage of received dataReal-Time Interactive Audio and Video Allow people to use audio/video to communicate with each other in real timeInternet phone, video conferencingEnd-end delay requirements:audio: < 150 msec good, < 400 msec OK, higher delays impair interactivityVideo: a few hundred msec acceptableRigid constraint on delay jitterdelay jitter: the variability of packet delays within the same packet streamconstant bit ratetransmissionCumulative datatimevariablenetworkdelay(jitter)clientreception constant bit rate playout at clientclient playoutdelaybuffereddataDelay JitterMultimedia Over Today’s InternetIP: best-effort serviceno guarantees on delay, lossBut multimedia apps require QoS to be effective!QoS: network provides application with level of performance needed for application to function.Today’s Internet multimedia applications use application-level techniques to mitigate(as best possible) effects of delay, lossHow Should the Internet Evolve to Better Support Multimedia?Integrated services philosophy: Fundamental changes in Internet so that apps can reserve end-to-end bandwidthRequires new, complex software in hosts & routersLaissez-faire approachno major changes in InternetISPs add more bandwidth when neededcontent distribution networks, multicast overlay networksDifferentiated services philosophy:Make relatively small changes to Internet infrastructureIntroduce a small number of traffic classes with different levels of
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