Project proposal Multi-stream and multi-path audio transmission

1. Project proposalMulti-stream and multi-path audio transmission

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 1 2 2 3 3 4 4 5 5 6

4. Loss recovery with multi-stream 4.5 4 3.5 m=2 3 2.5 m=3 Loss length of audio (packets) 2 1.5 m=4 1 0.5 0 1 2 3 4 5 6 7 8 9 10 # of consec. lost packet QoS improvement with multi-stream (1) – loss recovery • 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 1 2 3 4 5 Multi-stream s2 1 2 2 3 3 4 4 5 5 6 Delay=0 FEC protected single-stream [Bolot, 96’] 1 1 2 3 2 3 4 Packet Loss 1 2 1 3 4 3 Reconstructed 1 2 3 4 Two copies of payload data Delay=1 packet

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 R • 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.