A Model for MPEG with Forward Error Correction (FEC) and TCP-Friendly Bandwidth Huahui Wu, Mark Claypool & Robert Kinicki Computer Science Department Worcester Polytechnic Institute Worcester, MA, USA

6/3/2003 NOSSDAV 2003 Monterey, California #2 Outline Introduction Protocol Repair Related Knowledge Analytical Model Analytical Experiments Simulation Experiments Summary

6/3/2003 NOSSDAV 2003 Monterey, California #3 Transmission Protocol TCP uses retransmission No good for interactive application UDP have no retransmission It doesn ’ t respond to congestion TCP-Friendly [FHPW00] [RHE99] Well behavior protocol Loss is still an important issue

6/3/2003 NOSSDAV 2003 Monterey, California #4 Repair and Forward Error Correction Packet loss degrades the quality FEC adds redundancy and fixes loss Increase congestion to video stream Prior Approaches Ad-hoc Not TCP-Friendly Our Approach: Adjusting FEC with TCP-Friendly bandwidth constraint.

6/3/2003 NOSSDAV 2003 Monterey, California #5 Outline Introduction Related Knowledge MPEG Forward Error Correction TCP-Friendly Analytical Model Analytical Experiments Simulation Experiments Summary

6/3/2003 NOSSDAV 2003 Monterey, California #6 MPEG Three types of frames I (Intra-coded): Coded independently P (Predictive-coded): obtain prediction from preceding I or P frame B (Bidirectional predictive-coded): obtain prediction from the preceding and succeeding I or P frames Group of Picture (GOP)

6/3/2003 NOSSDAV 2003 Monterey, California #7 Forward Error Correction (FEC) Packet loss degrades video quality. FEC adds redundancy to recover from losses. With an MPEG frame made up of K ordinary packets, FEC adds N-K redundant packets to frame. If K or more of the N packets are received, the original frame can be successfully reconstructed. The successful frame transmission probability is (2)

6/3/2003 NOSSDAV 2003 Monterey, California #8 TCP-Friendly Flows Unresponsive flows get unfair share of network bandwidth and AQM techniques will punish them. Streaming flows need to be TCP-Friendly. A TCP-Friendly flow ’ s bandwidth is no more than a conformant TCP flow running under comparable network conditions. [PFTK98] (1)

6/3/2003 NOSSDAV 2003 Monterey, California #9 Outline Introduction Related Knowledge Analytical Model Successful Frame Transmission Probability GOP Rate Playable Frame Rate Analytical Experiments Simulation Experiments Summary

6/3/2003 NOSSDAV 2003 Monterey, California #10 Successful Frame Transmission Probability (3)

6/3/2003 NOSSDAV 2003 Monterey, California #11 GOP Rate TCP Friendly Rate GOP Rate (GOP per second)

6/3/2003 NOSSDAV 2003 Monterey, California #12 Playable Frame Rate Model (1 of 2) Playable Frame Rate of I, P and B frames (4)

6/3/2003 NOSSDAV 2003 Monterey, California #13 Playable Frame Rate Model (2 of 2) Given values of loss rate and frame size, the total playable frame rate can be estimated with the FEC and GOP pattern. The best playable frame rate can be obtained by searching the FEC and GOP space. (5)

6/3/2003 NOSSDAV 2003 Monterey, California #14 Outline Introduction Related Knowledge Analytical Model Analytical Experiments Methodology Improvement on Playable Frame Rate The Behaviors of FEC Simulation Experiments Summary

6/3/2003 NOSSDAV 2003 Monterey, California #15 Methodology Given a p, compute TCP-Friendly rate T. With a specific GOP and FEC pattern, the playable frame rate R can be computed. Search for the maximum rate Rm with all possible GOP and FEC pattern. Investigate the improvement from adjusting FEC, and the FEC behavior.

6/3/2003 NOSSDAV 2003 Monterey, California #16 Improvement of Playable Frame Rate RTT: 50ms s: 1KB p(%):0.5, 1, 2, 3, 4, … 10 SI: 25 packets SP: 8 packets SB: 3 packets [KSH95] GOP: IBBPBBPBBPBBPBB

6/3/2003 NOSSDAV 2003 Monterey, California #17 Adjusted FEC pattern Y-axis: Number of packets, X-axis: Loss percentage

6/3/2003 NOSSDAV 2003 Monterey, California #18 AFEC’s Advantage Successful frame transmission Probability a. Non-FEC b. Adjusting FEC

6/3/2003 NOSSDAV 2003 Monterey, California #19 Fixed FECs vs. Adjusted FEC Small: (1,1,0); Medium: (4,2,0); Large FEC: (8,4,1)

6/3/2003 NOSSDAV 2003 Monterey, California #20 Outline Introduction Related Knowledge Analytical Model Analytical Experiments Simulation Experiments Simulation of Dependent Packet Loss Simulation of Variable Round Trip Time Summary

6/3/2003 NOSSDAV 2003 Monterey, California #21 Simulation of Dependent Packet Loss Losses are often dependent Dependent loss reduce the effect of FEC Cause a lower playable frame rate

6/3/2003 NOSSDAV 2003 Monterey, California #22 Simulation of Variable Round Trip Time a. Distribution of RTT [CCZ03] b. Effect of Variable RTT

6/3/2003 NOSSDAV 2003 Monterey, California #23 Outline Introduction Related Knowledge Analytical Model Analytical Experiments Simulation Experiments Summary Contribution Ongoing Work

6/3/2003 NOSSDAV 2003 Monterey, California #24 Contribution Built a model to estimate the playable frame rate for TCP-Friendly MPEG Streaming. Used the model to study adjusting FEC and GOP behavior Adjusting FEC provides large benefit. 10 to 50 times improvement in playable frame rate with moderate to high loss probability. Adjusting GOP provides little benefit. More details are in the paper.

6/3/2003 NOSSDAV 2003 Monterey, California #25 Ongoing Work Model verification with realistic network TCP-Friendly Video Streaming with other repair techniques. Adjusting FEC combined with Media Scaling Build into NS-2 Simulator Implement it in real network

A Model for MPEG with Forward Error Correction (FEC) and TCP-Friendly Bandwidth Huahui Wu, Mark Claypool & Robert Kinicki Computer Science Department Worcester Polytechnic Institute Worcester, MA, USA

6/3/2003 NOSSDAV 2003 Monterey, California #27 Benefits from Adjusting FEC and/or GOP RTT: 50ms s: 1KB p(%):0.5, 1, 2, 3, 4, … 10 SI: 25 packets SP: 8 packets SB: 3 packets