Adjusting Forward Error Correction for TCP- Friendly Streaming MPEG

1
Adjusting Forward Error Correction for TCP-
Friendly Streaming MPEG

• Huahui Wu, Mark Claypool Robert Kinicki
• Computer Science Department
• Worcester Polytechnic Institute
• Worcester, MA, 01609 USA
• flashine,claypool,rek_at_cs.wpi.edu

2
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 flows bandwidth is no more than
  a conformant TCP flow running under comparable
  network conditions.

PFTK98
3
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

4
MPEG with FEC

• Prior Approaches
• were ad-hoc and did not consider
  TCP-Friendliness.
• Our Approach Adjusting FEC and GOP
• Forces TCP-Friendly bandwidth constraint.
• Develops an analytic model to compute playable
  frame rate for given FEC and GOP pattern.
• Exhaustively searches for FEC and GOP pattern
  that optimizes playable frame rate.

5
Playable Frame Rate Model (1 of 2)

• GOP rate (Group of Pictures per second)

• Playable Frame Rate of I, P and B frames

6
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.

7
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
8
Adjusted GOP and FEC pattern
Adjusted GOP pattern Y-axis Number of
frames X-axis Loss percentage
Adjusted FEC pattern Y-axis Number of
packets X-axis Loss percentage
9
Contribution Summary

• Contribution
• Built a model to estimate the playable frame rate
  with GOP and FEC pattern for MPEG.
• Used the model to study adjusting FEC and GOP
• Adjusting FEC provides large benefit.
• Adjusting GOP contributes little improvement.
• Ongoing Work
• Model verification with realistic network
• Adjustable FEC combined with Media Scaling.