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Video Streaming Over Wireless: Where TCP is Not Enough

Video Streaming Over Wireless: Where TCP is Not Enough. Xiaoqing Zhu, Jatinder Pal Singh and Bernd Girod. Information Systems Laboratory Stanford University. Wireless Home Networking. 6 Mbps. 24 Mbps. 54 Mbps. 12 Mbps. Outline. TCP throughput over wireless

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Video Streaming Over Wireless: Where TCP is Not Enough

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  1. Video Streaming Over Wireless: Where TCP is Not Enough Xiaoqing Zhu, Jatinder Pal Singh and Bernd Girod Information Systems Laboratory Stanford University

  2. Wireless Home Networking 6 Mbps 24 Mbps 54 Mbps 12 Mbps

  3. Outline • TCP throughput over wireless • Demo: video streaming vs. file transfer • Comparison with ideal solution • What’s missing in TCP?

  4. Heterogeneity in Wireless Link Speeds CN C1 Cl … Channel Time

  5. Stream 1 ) ) ) ) ) 54Mbps 6 ~ 54 Mbps ) ) ) ) ) Stream 2 UDP Throughput over Wireless Simulation in NS2, for 802.11a network 30 Stream 1, alone 25 Stream 2, alone 20 Stream 1, shared Throughput (Mbps) 15 10 Stream 2, shared 5 0 10 20 30 40 50 Nominal Speed of Second Link (Mbps)

  6. Stream 1 ) ) ) ) ) 54Mbps 6 ~ 54 Mbps ) ) ) ) ) Stream 2 TCP Throughput over Wireless Simulation in NS2, for 802.11a network 20 Stream 1, alone 15 Stream 2, alone Throughput (Mbps) Stream 1, shared 10 Stream 2, shared 5 0 10 20 30 40 50 Nominal Speed of Second Link (Mbps)

  7. Overhead of TCP ACK

  8. Scenario A Demo: Two Nodes Video Source @ 2Mbps Link Speed: 11 Mbps Throughput : 4.4 Mbps Shared : 1.0 Mbps (~ 20 % channel time) Shared : 1.0 Mbps (~ 70% channel time) File Transfer Source: 3.7MB Link Speed: 2 Mbps Throughput : 1.4 Mbps

  9. TCP Performance Video Streaming @ 2 Mbps … ~ 30 s Rate File Transfer @ 1.0 Mbps Time

  10. What Could Have Happened … Video Streaming @ 2 Mbps … Rate File Transfer @ 0.7 Mbps ~ 42 s Time

  11. Scenario B Link Speed: 2 Mbps File Transfer Source: 3.7MB Throughput : 1.4 Mbps Shared : 1.2 Mbps (~ 85% Channel Time) Shared : 1.2 Mbps (~ 6% Channel Time) Link Speed: 54 Mbps Throughput : 20 Mbps Video Source @ 3 Mbps

  12. TCP Performance Video Streaming @ 3 Mbps … Rate ~ 25 s File Transfer @ 1.2 Mbps Time

  13. What Could Have Happened … Video Streaming @ 3 Mbps … Rate ~ 27 s File Transfer @ 1.2 Mbps Time

  14. What’s Missing in TCP? • Awareness of application’s utility function • For file transfer, aggregate rate matters • For video streaming, instantaneous rate matters • Video streams differ in their rate-quality tradeoffs • Utility function only needed at the source • Knowledge of wireless link heterogeneity • Channel time shared among competing links • Congestion due to neighboring transmissions • High rate over a fast link vs. low rate over a slow link • End-to-end measurement no longer suffices • Notion of fairness should be revisited

  15. Clean Slate Design or Evolution?

  16. TCP Throughput over Wireless • Per-packet fairness at the MAC layer • Similar end-to-end observations of p, and RTT for competing wireless links • Approximately equal rate, regardless of link speed packet size data rate [Heusse et al. 2003] packet loss rate round trip time [Mahdavi, Floyd 1997] [Floyd et al. 2000]

  17. Stream 1 Stream 2 TCP Throughput over Wireless Simulation in NS2, for 802.11a network ) ) ) ) ) 54Mbps 6 ~ 54 Mbps ) ) ) ) )

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