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  • Streaming audio and video Has gone from novel technology in the 1990s into mainstream in Internet today By some estimates (RealNetworks G2 paper) there are hundreds of thousands of hours of media streamed each week on the Internet Traditional studies of Internet performance are not sufficient to characterize performance of video Bandwidth alone is not enough since a smooth delivery is needed also Response time is not enough since the stream is continuous Packet loss rate is not enough since streaming media often uses repair techniques to repair streams damaged by packet loss Our goal measure RealVideo performance on the Internet to Better understand the impact of video on the Internet Better understand the impact of the Internet on streaming video
  • Server-Player protocol RTSP for control UDP or TCP for data Progressive Networks Architecture (PNA) for backward compatibility HTTP if going through a firewall Buffering (also called preroll) for smoothness in the face of bandwidth changes SureStream different bandwidth encodings of the same clip can switch on fly Scalable video technology Data and frame rate controlled by client speed Audio data gets priority. If bwdith left, then video. Repair Forward Error Correction Interleaving (at least for audio)
  • On average, about 10% of the time a clip was selected it was unavailable. Not all clips on the server Not the same clips Future work to figure out why
  • Triangles represent RealServers Circles represent uses in our study Large circles represent clusters of users in our study
  • Playlist contained 98 clips Since playing the entire playlist took over 2 hours and users sometimes had trouble with their connection or RealPlayer, users often did not play the entire playlist Median user played about 50 clips 30% of users played 15 clips or fewer 30% of users played 80 clips or more
  • RealTracer

    1. 1. An Empirical Study of RealVideo Performance Across the Internet Yubing Wang, Mark Claypool and Zheng Zuo
    2. 2. Introduction <ul><li>Streaming Audio and Video is growing </li></ul><ul><li>Traditional Internet studies, but …. video is different </li></ul><ul><ul><li>Bandwidth and response time not enough </li></ul></ul><ul><ul><ul><li>Care about smooth rate </li></ul></ul></ul><ul><ul><li>Packet loss rate alone is not enough </li></ul></ul><ul><ul><ul><li>Often use repair techniques </li></ul></ul></ul><ul><li>RealVideo is big [Jup01] </li></ul><ul><ul><li>RealPlayer, MediaPlayer, QuickTime </li></ul></ul> Measure RealVideo on Internet
    3. 3. Outline <ul><li>Introduction </li></ul><ul><li>RealVideo  </li></ul><ul><li>Methodology </li></ul><ul><li>Results </li></ul><ul><li>Analysis </li></ul><ul><li>Conclusions </li></ul>
    4. 4. RealVideo Network Characteristics <ul><li>Buffering </li></ul><ul><li>SureStream </li></ul><ul><li>Scalable Video Technology </li></ul><ul><li>Repair </li></ul>Server RTSP Data: TCP or UDP
    5. 5. Outline <ul><li>Introduction </li></ul><ul><li>RealVideo </li></ul><ul><li>Methodology  </li></ul><ul><li>Results </li></ul><ul><li>Analysis </li></ul><ul><li>Conclusions </li></ul>
    6. 6. Methodology <ul><li>Build customized RealVideo player ( RealTracer ) </li></ul><ul><ul><li>Uses RealPlayer core </li></ul></ul><ul><ul><li>Software Development Kit (SDK) </li></ul></ul><ul><ul><li>Records performance stats: frame rate, jitter …. </li></ul></ul><ul><li>Select diverse set of RealVideo servers and videos </li></ul><ul><li>Solicit volunteers to run RealTracer </li></ul><ul><ul><li>Many users to Many servers </li></ul></ul><ul><ul><li>Friends, colleagues outside of Mass., U.S. </li></ul></ul><ul><ul><li> newsgroup and end2end mailing list </li></ul></ul><ul><ul><li>2 weeks in June 2001 </li></ul></ul><ul><li>Analyze results </li></ul>
    7. 7. Outline <ul><li>Introduction </li></ul><ul><li>RealVideo </li></ul><ul><li>Methodology </li></ul><ul><li>Results  </li></ul><ul><li>Analysis </li></ul><ul><li>Conclusions </li></ul>
    8. 8. Results <ul><li>11 servers in 8 countries </li></ul><ul><li>63 users in 12 countries </li></ul><ul><li>2855 video clips played </li></ul><ul><li>388 video clips watched and rated </li></ul><ul><li>10% chance clip unavailable </li></ul>
    9. 9. Geographic Location of Servers and Clients
    10. 10. Clips Played per User
    11. 11. Outline <ul><li>Introduction </li></ul><ul><li>RealVideo </li></ul><ul><li>Methodology </li></ul><ul><li>Results </li></ul><ul><li>Analysis </li></ul><ul><ul><li>Frame Rate  </li></ul></ul><ul><ul><li>Jitter </li></ul></ul><ul><ul><li>Perceived Quality </li></ul></ul><ul><li>Conclusions </li></ul>
    12. 12. Frame Rate <ul><li>Basic video performance unit </li></ul><ul><ul><li>frames per second (fps) </li></ul></ul><ul><li>Guidelines [Rea00a]: </li></ul><ul><ul><li>24-30 fps: full-motion video </li></ul></ul><ul><ul><li>15 fps: full-motion video approximation </li></ul></ul><ul><ul><li>7 fps: choppy </li></ul></ul><ul><ul><li>3 fps: very choppy </li></ul></ul><ul><ul><li>Less than 3 fps: slide show </li></ul></ul>
    13. 13. Overall Frame Rate
    14. 14. Frame Rate vs. Network Configuration Modem: 19% (550) DSL/Cable: 30% (874) T1/LAN: 51% (1468)
    15. 15. Bandwidth vs. Network Configuration
    16. 16. Outline <ul><li>Introduction </li></ul><ul><li>RealVideo </li></ul><ul><li>Methodology </li></ul><ul><li>Results </li></ul><ul><li>Analysis </li></ul><ul><ul><li>Frame Rate </li></ul></ul><ul><ul><li>Jitter  </li></ul></ul><ul><ul><li>Perceived Quality </li></ul></ul><ul><li>Conclusions </li></ul>
    17. 17. Jitter <ul><li>Frame rate alone not enough </li></ul><ul><ul><li>Also need smooth playout </li></ul></ul><ul><ul><li>High frame rate but choppy playout can be as bad as frame loss [CT99] </li></ul></ul><ul><li>Variation in frame playout interval called jitter </li></ul><ul><ul><li>Standard deviation </li></ul></ul><ul><li>Buffering can reduce jitter [RKTS94, SJ95 ] </li></ul><ul><ul><li>But can still have residual jitter </li></ul></ul><ul><li>Quantitative impact of residual jitter on perceived quality scarce </li></ul><ul><ul><li>50 ms imperceptible, 300 ms very rough </li></ul></ul>
    18. 18. Overall Jitter
    19. 19. Jitter vs. Network Configuration
    20. 20. Outline <ul><li>Introduction </li></ul><ul><li>RealVideo </li></ul><ul><li>Methodology </li></ul><ul><li>Results </li></ul><ul><li>Analysis </li></ul><ul><ul><li>Frame Rate </li></ul></ul><ul><ul><li>Jitter </li></ul></ul><ul><ul><li>Perceived Quality  </li></ul></ul><ul><li>Conclusions </li></ul>
    21. 21. Perceived Quality <ul><li>Frame Rate and Jitter not enough </li></ul><ul><ul><li>Best frame rate depends upon content [TC01] </li></ul></ul><ul><ul><ul><li>RealServer varies </li></ul></ul></ul><ul><ul><li>Effects of jitter depend upon content [CT99] </li></ul></ul><ul><li>Perceptual Quality </li></ul><ul><ul><li>Numeric rating, 0-10 </li></ul></ul>
    22. 22. Clips Rated per User (388 video clips rated)
    23. 23. Quality vs. Network Configuration
    24. 24. Conclusions <ul><li>Average RealVideo clip has good quality </li></ul><ul><ul><li>10 frames per second </li></ul></ul><ul><ul><li>Nearly imperceptible jitter </li></ul></ul><ul><li>Network configuration </li></ul><ul><ul><li>Modems are a bottleneck </li></ul></ul><ul><ul><li>DSL/Cable modems pushing bottleneck towards server </li></ul></ul>
    25. 25. Future Work <ul><li>RealVideo over UDP </li></ul><ul><ul><li> TCP-Compatible? </li></ul></ul><ul><li>Perceptual quality of streaming video </li></ul><ul><li>Other streaming players and protocols </li></ul><ul><ul><li>MediaPlayer, QuickTime </li></ul></ul><ul><li>Effects of caching, CDNs </li></ul><ul><li>Release of customizable RealTracer </li></ul><ul><li>Download IP addresses, Playlist, RealTracer </li></ul><ul><ul><li>From Web page </li></ul></ul>
    26. 26. An Empirical Study of RealVideo Performance Across the Internet Yubing Wang, Mark Claypool and Zheng Zuo