Quality of Service in the Internet The 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: r delay sensitive r loss tolerant: infrequent losses cause minor glitches r Different from elastic applications (e.g., file transfer, Web, , telnet), which are loss intolerant and delay tolerant

Classes of Multimedia Applications r Streaming stored audio and video r Streaming live audio and video r Real-time interactive audio and video

Streaming Stored Audio and Video r Prerecorded media stored on servers, media transmitted to client on demand m Examples: audio of a lecture, archives of radio broadcasts, movies, MTV clips r Streaming: client playout begins before all data has arrived m buffer needed at client r Delay constraint: data must be received in time for playout at the client r Interactivity: client can pause, rewind, fast- forward m 1-2 sec until command effect OK

Streaming Live Audio and Video r Examples: Internet radio talk show, live sporting event Streaming r playback buffer at client r playback can lag tens of seconds after request r delay constraint: data must be received in time for playout at the client Interactivity r Not stored  fast forward impossible r rewind, pause possible with local storage of received data

Real-Time Interactive Audio and Video r Allow people to use audio/video to communicate with each other in real time m Internet phone, video conferencing r End-end delay requirements: m audio: < 150 msec good, < 400 msec OK, higher delays impair interactivity m Video: a few hundred msec acceptable r Rigid constraint on delay jitter m delay jitter: the variability of packet delays within the same packet stream

constant bit rate transmission Cumulative data time variable network delay (jitter) client reception constant bit rate playout at client client playout delay buffered data Delay Jitter

Multimedia Over Today’s Internet r IP: best-effort service m no guarantees on delay, loss r But multimedia apps require QoS to be effective! m 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, loss

How Should the Internet Evolve to Better Support Multimedia? Integrated services philosophy: r Fundamental changes in Internet so that apps can reserve end- to-end bandwidth r Requires new, complex software in hosts & routers Laissez-faire approach r no major changes in Internet r ISPs add more bandwidth when needed r content distribution networks, multicast overlay networks Differentiated services philosophy: r Make relatively small changes to Internet infrastructure r Introduce a small number of traffic classes with different levels of service