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Quality of Service in the Internet

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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 sensitiveloss 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 videoStreaming live audio and videoReal-time interactive audio and videoStreaming Stored Audio and VideoPrerecorded media stored on servers, media transmitted to client on demandExamples: audio of a lecture, archives of radio broadcasts, movies, MTV clipsStreaming: client playout begins before all data has arrivedbuffer needed at clientDelay constraint: data must be received in time for playout at the clientInteractivity: client can pause, rewind, fast-forward1-2 sec until command effect OKStreaming Live Audio and VideoExamples: Internet radio talk show, live sporting eventStreamingplayback buffer at clientplayback can lag tens of seconds after requestdelay constraint: data must be received in time for playout at the clientInteractivityNot stored  fast forward impossiblerewind, 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 timeInternet phone, video conferencingEnd-end delay requirements:audio: < 150 msec good, < 400 msec OK, higher delays impair interactivityVideo: a few hundred msec acceptableRigid constraint on delay jitterdelay 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 InternetIP: best-effort serviceno guarantees on delay, lossBut 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 bandwidthRequires new, complex software in hosts & routersLaissez-faire approachno major changes in InternetISPs add more bandwidth when neededcontent distribution networks, multicast overlay networksDifferentiated services philosophy:Make relatively small changes to Internet infrastructureIntroduce a small number of traffic classes with different levels of


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