1. Project proposal Multi-stream and multi-path audio transmission
Feb. 1, 2001

2. Outline Multi-stream audio transmission Multi-stream vs. FEC
Rate and error control
Multi-stream using path diversity
Multi-path to improve QoS
Proposed work

3. Multi-stream audio transmission
The incentives
Best-effort services vs. strict QoS requirements of real-time speech communication, e.g. latency, loss, rate variation etc.
Low bandwidth of the voice stream
The scheme s1 1 2 3 4 5 s2
# of consecutive lost packet 1 2 3 … n
Loss length after recovery (packet) .5
n/2-.5

4. QoS improvement with multi-stream (1) – loss recovery2 3 4 5 6 7 8 9 10
0.5
1.5
2.5
3.5
4.5
# of consec. lost packet
Loss length of audio (packets)
Loss recovery with multi-stream
m=2
m=3
m=4
Loss recovery
With m streams, when having n consecutive lost packet, the loss after recovery is: max(n/m+1/m-1,0)
Stronger protection at the cost of higher data rate
Lower loss rate indicates delay reduction
loss
delay

5. QoS improvement with multi-stream (2) – delay reduction
Reduction of delay and playout rate variation

6. Multi-stream vs. FEC (1) s1 Multi-stream s2 FEC protected3 4 5
Multi-stream s2
Delay=0
FEC protected
single-stream
[Bolot, 96’] 1 1 2 3 2 3 4
Packet Loss 1 1 2 3 3 4
Reconstructed 1 2 3 4
Two copies of payload
data
Delay=1 packet
# of consecutive lost packet 1 2 3 … n
Loss length after recovery (packet)
n-1

7. Multi-stream vs. FEC (2) Both add redundancy for data protection
Pros of multi-stream:
Introduces lower delay for loss recovery
Provides stronger protection
Cons of multi-stream:
Overhead from packet header is higher
Smaller transmission interval

8. Joint rate and error-protection control for multi-stream
What if network congestion?
Decreasing audio stream rate does not necessarily alleviate the problem
Add stronger protection against loss and delay variation without increasing the total rate
Solution: use more streams with different speech codec
One more issue: header compression

9. Multi-stream with path diversity
Packets from source to destination sent explicitly over different links to use path diversity
Previous work on path diversity:
Internet path selection [Savage, 99’]
One paper on reliable video comm. using MSE [Apostolopoulos, VCIP 01’]
Network behavior averaged
Burst loss converted to isolated loss
Outage probability decreased

10. Multi-stream audio transmission using path diversity
Path diversity for real-time speech communication: reduced variation of network delay by selecting path
Can reduce playout delay and speech rate variation 1
Relay
Relay 2
Internet
traffic
Internet
traffic S
The bottleneck

11. Path diversity to improve QoS
Loss recovery: stronger protection than single path multi-stream
Reduction of delay and playout rate variation

12. Delay reduction (2)
Adaptive playout scheduling and speech scaling makes seamless switching between streams possible

13. Proposed work (1) For single path multi-stream
Compare the performance of multi-stream and single-stream FEC at the same rate. Find the the packet loss/delay jitter behavior by ns simulation.
- Has to use ns simulator – must compare the two schemes under the same traffic statistics. Experiments must be repeatable.
Study on the optimal rate and error control.

14. Proposed work (2) For multi-path transmission
ns simulation based on reasonable network topology and traffic model.
- Network measurement in the real world is difficult. Relay server network, opt. path selection not available at present.
Design of the adaptive playout scheduling algorithm suitable for multi-stream.
Study the QoS improvement by using path diversity.