1 / 34

Flow control for multimedia streaming using TEAR (TCP emulation at receivers) work in progress.

Flow control for multimedia streaming using TEAR (TCP emulation at receivers) work in progress. Injong Rhee Department of Computer Science North Carolina State University. Multimedia streaming over the Internet. Internet. Video and audio streaming over the Internet becomes popular.

timberly-richardson
Download Presentation

Flow control for multimedia streaming using TEAR (TCP emulation at receivers) work in progress.

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Flow control for multimedia streaming using TEAR (TCP emulation at receivers)work in progress. Injong Rhee Department of Computer Science North Carolina State University

  2. Multimedia streaming over the Internet Internet • Video and audio streaming over the Internet becomes popular. • As last mile network bandwidth increases (ADSL, Cable modems, Satellite), multimedia traffic will constitute a large portion of Internet traffic. • The VoD market will grow accordingly (e.g., AOL + TW).

  3. Congestion and flow ControlThe adaptive, best-effort, congestion control problem • End-to-end congestion control. • How can we make the best use of the (time varying) bandwidth that is available to our streams? • How can we determine what this bandwidth is? • How can we track how it changes over time? Switch Fabric Switch Fabric

  4. TCP • Constitutes more than 70%-90% of the Internet traffic. • Employs AIMD (additive increase and multiplicative decrease) for fairness • Congestion indications (packet losses) trigger multiplicative reduction in its transmission rate.

  5. TCPbackground - AIMD • Maintains cwnd (congestion window) at the sender by receiving acknowledgment from the receiver; • Transmits a cwnd number of packets per round (or per RTT). Packet loss Packet loss Packet loss TIMEOUT ssThresh Congestion Window Fast recovery (cwnd is halved) Rounds (reception of cwnd packets) Congestion avoidance Slow start

  6. TCP and TCP-friendliness • Non-responsive flows can lock out TCP flows completely;congestion collapse will result. • TCP-friendliness: a TCP friendly flow uses the same bandwidth as a competing TCP flow on the same end-to-end path.

  7. Multimedia applications • Unfortunately, few multimedia streaming commercial applications today employ TCP-friendly flow control.

  8. TCP+multimedia applications?Is TCP a good choice for multimedia applications? • Not a good marriage. • TCP transmission is too bursty • ack compression especially under high RTT. • TCP’s rate is highly fluctuating • A single packet loss can swing the rate to half the current rate or to almost zero under timeout.

  9. Poor performance under asymmetric networks (ADSL,Satellite) Per-packet feedback causes congestion on the reverse path. Feedback loss in the reverse path can cause rate reduction in the forward path. Scalability limitations in multicast environments. Per-packet feedback can cause feedback implosion. TCP+multimedia applications?Is TCP a good choice for multimedia applications?

  10. Existing approachesSAD(sender-driven AIMD) • Jacobs’97, Cen’98, Rejaie’99, etc. • Performs AIMD at the sender • Provably stable and fair • Contains the same limitations as TCP. • Per-packet feedback: its performance limitation under asymmetric networks or multicast environments. CWND Time

  11. Existing approachesMFC (Model-based flow control) or equation-based flow control. • Use a stochastic TCP model • Mahdavi&Floyd’97,Floyd’99, Padhey’99,etc. • Gives a simple analytical formula for TCP throughputin a function of packet loss rate and RTT. • Receiver can estimate TCP throughput using the formula. The sender sets its xmission rate to R Compute TCP Throughput using the formula. Report rate R. Sender Receiver

  12. Existing approachesMFC – fundamental problems. Probability of loss event within a window Loss Rate = Number of packets in a window • [Ramesh&Rhee’99] analytically shows that under certain circumstances, MFC does not converge to the fair bandwidth. • Due to inherent error in estimating loss rates and in the formula. E.g., • Under a high transmission rate, the loss rate can be underestimated, and under a low transmission rate, the loss rate can be overestimated. • Assumptions made by the model are not universally true. • E.g., loss rates or RTTs are not correlated to the transmission rate of the MFC flows.

  13. TEAR: TCP Emulation At Receivers our approach – overview I • Shift most of flow control functions to receivers. • Instead of reporting congestion signals, process them immediately at receivers. • Receivers emulate the TCP window adjustment protocol. • Increase: congestion avoidance and slow start. • Decrease: fast recovery and timeout. CWND The sender sets its xmission rate to R Emulate TCP window adjustment Report rate R. Sender Receiver

  14. TEAR: TCP Emulation At Receivers our approach – overview II Emulate TCP window adjustment Report rate R. Receiver • Instead of reporting an instantaneous (oscillating) rate, the receiver can find the equilibrium operating point (more smoothed averaged rate) Perform smoothing using Weighted averaging Equilibrium operating point

  15. TEAR in action10MB droptail, 8 TCPs, 8 TEARs

  16. TEARBasic window emulation functions - round A round contains roughly an arrival of cwnd packets. CWND one TCP round CWND one TEAR round Round in TEAR Round in TCP

  17. TEARBasic window emulation functions – window increase • Slow start: cwnd is doubled per round. • Congestion avoidance: cwnd is increased by one per round. cwnd 1 2 4 8 9 10 Slow start Congestion avoidance

  18. TEARFast Recovery Triple duplicate acknowledgments cwnd:5 TCP TCP sender detects fast recovery here. TEAR receiver detects fast recovery here cwnd:5 TEAR Ignore packet losses in next RTT period

  19. TEARTimeout - I • In TCP, after an initial packet loss in a window, at least cwnd packets are sent (including the lost packet) – this is true no matter which packet is lost in that window. • If TCP sender does not detect FR by the timethat these packets wound be acknowledged (some of them would be lost), timeout will occur. Only two TDs received cwnd:5 Timeout TCP

  20. TCPTimeout - II • If TEAR receiver does not detect FR before the reception ofa packet with x+cwnd-1 or higher after the initial loss (including the lost packet), then TEAR enters timeout. • Or, Ttimeout (= Tinterarrival * cwnd * 2DEV) has expired after the initial packet loss. TEAR receiver detects timeout cwnd:5 X+4 X TEAR Ignore packet losses in next RTT period

  21. Performance evaluation • Simulation (NS) • Internet experiments 20Mb/s, 10ms 20Mb/s, 10ms xx MB/s, 10ms n0 n1 n2 n3 10Mbs (somewhere in Korea) RTT 205 ms 40Mb/s – 186Mb/s RTT 60 – 100 ms UCSD Korea NCSU NCSU

  22. SimulationFairness and TCP-friendliness - I • 10Mbs, 8 TEARs (or TFRCs), 8 TCPs, Droptail TEAR TFRC

  23. SimulationFairness and TCP-friendliness - II • 2.5Mbs, 8 TEARs (or TFRCs), 8 TCPs, Droptail TFRC TEAR

  24. Simulation Fairness and TCP-friendliness - III • Equivalence factor of two flows A, B : Min (A/B, B/A). Min (TEAR/TCP, TCP/TEAR). Min (TFRC/TCP, TCP/TFRC).

  25. Internet experiments (Korea, UCSD)Fairness and TCP-friendliness - III • Measured every hour in the 3rd week of March. UCSD Korea

  26. SimulationRate fluctuations - I

  27. Internet experimentsRate fluctuations (coefficients of variance) - II • Coefficients of variable: ratio of one stand. Dev to average. TEAR TCP

  28. SimulationFeedback latency sensitivity - TEAR

  29. SimulationFeedback latency sensitivity - TFRC

  30. Summary and Future work • TEAR shifts most of functions to receivers. • By emulating TCP functions at receivers, receivers find TCP-friendly rates. • We report work-in-progress; needs more work. • what is the time scale of response? • What is the tradeoffs between different filtering functions at receivers for rate smoothing? • Run experiments with real multimedia data. • ….

  31. Future workmulticast - Layered multicast • Receiver-driven layered multicast • Receivers can estimate their receiving rates using TEAR and join and leave multicast groups based on the estimate rates. E 1Mbs A B D 5Mbs 10Mbs 5Mbs C

  32. Future workmulticast - Sender-based single rate multicast • SSRM - sender picks the minimum rate reported by receivers. • Feedback implosion • Filtering for drop-to-zero problem. • …. Sender Feedback/filtering mechanism

  33. Future workMiddleware support Application Interface Group membership, Delivery semantics (Convenient, but application malleable) Flow and Congestion Control (no dependency on particular recovery mechanisms) Loss Recovery reliable, best effort, or application specific

  34. TEARRate independence – basic assumption • Rate independence: the probability of having at least a loss in a window of size x in TEAR is the same as that in TCP competing on the same end-to-end path. Sampling instances TCP TEAR

More Related