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  • Now present example system, where we have used the idea of resource allocation for maximum total utility. Problem: distribution of Internet video over a home network. Many countries: phone outlet is in the hallway, and DSL box. How to get video to the living room, den, or whereever else without running wires? WLAN, 802.11 Problem: different link-rates Problem: interference, for example from microwave ovens and chordless phones
  • Could have sustained video streaming with 10% increase in file transfer time
  • Prsentation Slides

    1. 1. Video Streaming Over Wireless: Where TCP is Not Enough Xiaoqing Zhu, Jatinder Pal Singh and Bernd Girod Information Systems Laboratory Stanford University
    2. 2. Wireless Home Networking 54 Mbps 6 Mbps 24 Mbps 12 Mbps
    3. 3. <ul><li>TCP throughput over wireless </li></ul><ul><li>Demo: video streaming vs. file transfer </li></ul><ul><li>Comparison with ideal solution </li></ul><ul><li>What’s missing in TCP? </li></ul>Outline
    4. 4. Heterogeneity in Wireless Link Speeds C 1 C l C N Channel Time …
    5. 5. UDP Throughput over Wireless 10 20 30 40 50 0 5 10 15 20 25 30 Nominal Speed of Second Link (Mbps) Throughput (Mbps) Simulation in NS2, for 802.11a network Stream 1, alone Stream 2, alone Stream 1, shared Stream 2, shared 54Mbps ) ) ) ) ) ) ) ) ) ) Stream 2 Stream 1 6 ~ 54 Mbps
    6. 6. TCP Throughput over Wireless 10 20 30 40 50 0 5 10 15 20 Nominal Speed of Second Link (Mbps) Throughput (Mbps) Simulation in NS2, for 802.11a network Stream 1, alone Stream 2, alone Stream 1, shared Stream 2, shared 54Mbps ) ) ) ) ) ) ) ) ) ) Stream 2 Stream 1 6 ~ 54 Mbps
    7. 7. Overhead of TCP ACK
    8. 8. Demo: Two Nodes Link Speed: 11 Mbps Throughput : 4.4 Mbps Shared : 1.0 Mbps (~ 20 % channel time) Link Speed: 2 Mbps Throughput : 1.4 Mbps Shared : 1.0 Mbps (~ 70% channel time) Video Source @ 2Mbps File Transfer Source: 3.7MB Scenario A
    9. 9. TCP Performance Video Streaming @ 2 Mbps Time Rate … File Transfer @ 1.0 Mbps ~ 30 s
    10. 10. What Could Have Happened … Rate Time … Video Streaming @ 2 Mbps File Transfer @ 0.7 Mbps ~ 42 s
    11. 11. Scenario B Link Speed: 54 Mbps Throughput : 20 Mbps Shared : 1.2 Mbps (~ 6% Channel Time) Link Speed: 2 Mbps Throughput : 1.4 Mbps Shared : 1.2 Mbps (~ 85% Channel Time) Video Source @ 3 Mbps File Transfer Source: 3.7MB
    12. 12. TCP Performance Time Video Streaming @ 3 Mbps File Transfer @ 1.2 Mbps ~ 25 s Rate …
    13. 13. What Could Have Happened … Rate Time Video Streaming @ 3 Mbps File Transfer @ 1.2 Mbps … ~ 27 s
    14. 14. What’s Missing in TCP? <ul><li>Awareness of application’s utility function </li></ul><ul><ul><li>For file transfer, aggregate rate matters </li></ul></ul><ul><ul><li>For video streaming, instantaneous rate matters </li></ul></ul><ul><ul><li>Video streams differ in their rate-quality tradeoffs </li></ul></ul><ul><ul><li>Utility function only needed at the source </li></ul></ul><ul><li>Knowledge of wireless link heterogeneity </li></ul><ul><ul><li>Channel time shared among competing links </li></ul></ul><ul><ul><li>Congestion due to neighboring transmissions </li></ul></ul><ul><ul><li>High rate over a fast link vs. low rate over a slow link </li></ul></ul><ul><ul><li>End-to-end measurement no longer suffices </li></ul></ul><ul><ul><li>Notion of fairness should be revisited </li></ul></ul>
    15. 15. Clean Slate Design or Evolution?
    16. 16. TCP Throughput over Wireless <ul><li>Per-packet fairness at the MAC layer </li></ul><ul><li>Similar end-to-end observations of p , and RTT for competing wireless links </li></ul><ul><li>Approximately equal rate, regardless of link speed </li></ul>packet size round trip time packet loss rate data rate [Mahdavi, Floyd 1997] [Floyd et al. 2000] [Heusse et al. 2003]
    17. 17. TCP Throughput over Wireless 54Mbps ) ) ) ) ) ) ) ) ) ) 6 ~ 54 Mbps Simulation in NS2, for 802.11a network Stream 2 Stream 1

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