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

2. X. Zhu et al: Video Streaming over Wireless April 1, 20082 Wireless Home Networking 54 Mbps 6 Mbps 24 Mbps 12 Mbps

3. X. Zhu et al: Video Streaming over Wireless April 1, 20083 TCP throughput over wireless Demo: video streaming vs. file transfer Comparison with ideal solution What’s missing in TCP? Outline

4. X. Zhu et al: Video Streaming over Wireless April 1, 20084 Heterogeneity in Wireless Link Speeds C1C1 ClCl CNCN Channel Time …

5. X. Zhu et al: Video Streaming over Wireless April 1, 20085 UDP Throughput over Wireless 1020304050 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. X. Zhu et al: Video Streaming over Wireless April 1, 20086 TCP Throughput over Wireless 1020304050 0 5 10 15 20 Nominal Speed of Second Link (Mbps) Throughput (Mbps) 54Mbps ) ) ) ) ) Stream 2 Stream 1 6 ~ 54 Mbps Simulation in NS2, for 802.11a network Stream 1, alone Stream 2, alone Stream 1, shared Stream 2, shared

7. X. Zhu et al: Video Streaming over Wireless April 1, 20087 Overhead of TCP ACK

8. X. Zhu et al: Video Streaming over Wireless April 1, 20088 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. X. Zhu et al: Video Streaming over Wireless April 1, 20089 TCP Performance Video Streaming @ 2 Mbps Time Rate … File Transfer @ 1.0 Mbps ~ 30 s

10. X. Zhu et al: Video Streaming over Wireless April 1, 200810 What Could Have Happened … Rate Time … Video Streaming @ 2 Mbps File Transfer @ 0.7 Mbps ~ 42 s

11. X. Zhu et al: Video Streaming over Wireless April 1, 200811 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. X. Zhu et al: Video Streaming over Wireless April 1, 200812 TCP Performance Time Video Streaming @ 3 Mbps File Transfer @ 1.2 Mbps ~ 25 s Rate …

13. X. Zhu et al: Video Streaming over Wireless April 1, 200813 What Could Have Happened … Rate Time Video Streaming @ 3 Mbps File Transfer @ 1.2 Mbps … ~ 27 s

14. X. Zhu et al: Video Streaming over Wireless April 1, 200814 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. X. Zhu et al: Video Streaming over Wireless April 1, 200816 TCP Throughput over Wireless packet size round trip time packet loss rate data rate [Mahdavi, Floyd 1997] [Floyd et al. 2000] 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 [Heusse et al. 2003]

17. X. Zhu et al: Video Streaming over Wireless April 1, 200817 TCP Throughput over Wireless 54Mbps ) ) ) ) ) Stream 2 Stream 1 6 ~ 54 Mbps Simulation in NS2, for 802.11a network