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, 01609 USA
{flashine,claypool,rek}@cs.wpi.edu
Outline
Introduction
Protocol
Repair
Related Knowledge
Analytical Model
Analytical Experiments
Simulation Experiments
Summary
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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
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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.
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Outline
Introduction
Related Knowledge
MPEG
Forward Error Correction
TCP-Friendly
Analytical Model
Analytical Experiments
Simulation Experiments
Summary
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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)
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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
N  N

 
i
N i
q( N , K , p)    (1  p)  p 
(2)
i  K  i 

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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.
s
(1)
T
2p
3p
t RTT
 t RTO (3
) p(1  32 p 2 )
3
8
[PFTK98]
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Outline
Introduction
Related Knowledge
Analytical Model
Successful Frame Transmission Probability
GOP Rate
Playable Frame Rate
Analytical Experiments
Simulation Experiments
Summary
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Successful Frame Transmission Probability
 N 

i
N i
q( N , K , p)    (1  p)  p 
i  K  i 

N
 qI  q( S I  S IF , S I , p)

qP  q( S P  S PF , S P , p)
q  q( S  S , S , p)
B
BF
B
 B
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GOP Rate
TCP Friendly Rate
s
T
t RTT
2p
3p
 t RTO (3
) p(1  32 p 2 )
3
8
GOP Rate (GOP per second)
T /s
G
( S I  S IF )  N P ( S P  S PF )  N B ( S B  S BF )
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Playable Frame Rate Model (1 of 2)
Playable Frame Rate
of I, P and B frames
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 RI  G  qI

i
 RPi  RI  q P
R  R  q
Pi 1
B
 Bij
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Playable Frame Rate Model (2 of 2)
R  RI   RPi   RBij
i
i, j
q P  q PN P 1
 G  q I  (1 
1  qP
N P 1
P
qP  q
 N BP  q B  (
1  qP
 qI  q
NP
P
))
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.
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(5)
Outline
Introduction
Related Knowledge
Analytical Model
Analytical Experiments
Methodology
Improvement on Playable Frame Rate
The Behaviors of FEC
Simulation Experiments
Summary
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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.
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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
GOP: IBBPBBPBBPBBPBB
[KSH95]
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Adjusted FEC pattern
10
SI F
SPF
SBF
8
6
4
2
0
1
2
3
4
5
6
7
8
9 10
Y-axis: Number of packets, X-axis: Loss percentage
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AFEC’s Advantage
a. Non-FEC
b. Adjusting FEC
Successful frame transmission Probability
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Fixed FECs vs. Adjusted FEC
Fixed FECs vs. Adjusted FEC
• Small: (1,1,0); Medium: (4,2,0); Large FEC: (8,4,1)
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Outline
Introduction
Related Knowledge
Analytical Model
Analytical Experiments
Simulation Experiments
Simulation of Dependent Packet Loss
Simulation of Variable Round Trip Time
Summary
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Simulation of Dependent Packet Loss
Losses are often dependent
Dependent loss reduce the effect of FEC
Cause a lower playable frame rate
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Simulation of Variable Round Trip Time
a. Distribution of RTT [CCZ03]
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b. Effect of Variable RTT
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Outline
Introduction
Related Knowledge
Analytical Model
Analytical Experiments
Simulation Experiments
Summary
Contribution
Ongoing Work
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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.
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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
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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, 01609 USA
{flashine,claypool,rek}@cs.wpi.edu
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
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