Multimedia Streaming via TCP: An Analytic Performance Study

1. Multimedia Streaming via TCP: An Analytic Performance Study Bing Wang, Jim Kurose, Prashant Shenoy, Don Towsley

2. Introduction • Under what circumstances can TCP streaming provide satisfactory performance? • Live video streaming is constrained streaming • Stored video streaming is unconstrained streaming

3. Outline • Analytic model • Simulation • Experiments • Effect of parameters on performance

4. Contribution of Paper • develop discrete-time Markov models for live and stored video streaming • explore how parameters (i.e. loss rate, round trip time, timeout value & playback rate) affect TCP streaming performance

5. Assumption • Average TCP throughput is no less than the video bitrate • Startup delay on the order of seconds • Videos are of constant bit rate (CBR)

6. Performance metrics • Fraction of late packets • no known metric directly for viewing quality

7. Notations

8. Model for TCP • time unit is round (length of a round = a round trip time) • Xi is the state of model in the ith round • Xi = (Wi, Ci, Li, Ei, Ri) • Wi = window size • Ci = delayed ACK behavior • Li = # packets lost in (i-1)th round • Ei = backoff exponent if in timeout state • Ri = 0 for new packet; =1 for retransmission

9. Model for streaming

10. Model for constrained streaming • Yi is the state of the model in the ith round • Yi = (Xi, Ni) • Xi = state of TCP (mentioned before) • Ni = # early packets

11. Model for unconstrained streaming • As length go to infinity, # early packets go to infinity and fraction of late packets go to zero • use transient analysis • Yi is the state of the model in the ith round • Yi = Xi

12. Model for unconstrained streaming • use impulse reward to obtain transient distribution of Ni • impulse reward = difference % # packets received and played back in transition • Ni’= accumulation of the impulse reward up to ith round

13. Model for unconstrained streaming

14. Simulation

15. Simulation

16. Simulation

17. Simulation

18. Simulation

19. Simulation

20. Simulation

21. Simulation

22. Experiments

23. Experiment

24. Experiment

25. Exploring parameter space

26. Effect of video length

27. Effect of T/μ

28. Sensitivity to parameters

29. Conditions for satisfactory performance

30. Summary of results • fraction of late packets increases with length in live streaming, but decreases with length in stored streaming • performance increases with T/μ; beyond a certain point yields diminishing gain • performance is not solely determined by T/μ but also sensitive to parameters like R, p, T0 • For large R, p and T0, either long startup delay or T/μ greater than 2 is needed for low fraction of late packets

31. Implication • large fraction of streaming video clips are encoded at 300Kbps • most DSL and cable modem connection support 750Kbps – 1.5Mbps • TCP streaming is adequate for broadband users

32. Conclusion • Discrete-time Markov models for live and stored video streaming • Simulation and experiments show models are accurate • Study effect of various parameters on performance with the models