Receiver Capability Heterogeneity in the Internet

1. Receiver Capability Heterogeneity in the Internet

2. Agenda • Introduction • Some proposed approaches • Performance comparison • Summary • Discussion

3. Introduction • Evolution of VoD systems • Video rental  Video over Internet • Unicast  Multicast 4 data streams 1 data stream VS 3 data streams 1 data stream

4. Introduction • Problem created by receiver capability heterogeneity 1 Mbps 3 Mbps

5. Introduction • Trivial solutions, we either • 1. leave video stream rate at 3 Mbps  Unable to provide real-time streaming • 2. reduce video stream rate to 1 Mbps  Video quality degradation

6. Other Approaches • Replicated stream approach • Layering approaches • Cumulative layering approach • Non-cumulative layering approach

7. Replicated Stream Approach • Aggregate server bandwidth: 4 Mbps Group of clients (CA) – downlink: 1 Mbps Sender Group of clients (CB) – downlink: 3 Mbps Full quality stream (3 Mbps) Low quality stream (1 Mbps)

8. Layering Approaches • Cumulative layering • Base layer + enhancement layers • Cumulative decoding • E.g. MPEG-2 and H.263 standards • Spatial scalability, temporal scalability, data partitioning and SNR scalability • Non-cumulative layering • Independently decodable video layers • E.g. Multiple Description Coding (MDC)

9. Layering Approaches • Aggregate server bandwidth: 3 Mbps Group of clients (CA) – downlink: 1 Mbps Sender Group of clients (CB) – downlink: 3 Mbps Enhancement layer (2 Mbps) Base layer (1 Mbps)

10. Comparison between the Two Approaches • Common argument: • Stream replication wastes server bandwidth by stream duplication • However, no quantitative and systematic comparison has been given

11. Some Counterarguments • Kim and Ammar [1] take into account of • Layering overhead • Protocol complexity for fair comparison [1] T. Kim, M. H. Ammar , "A comparison of layering and stream replication video multicast schemes", Proc. NOSSDAV‘ 01, Port Jefferson, NY, June 25-26, 2001.

12. Layering Overhead • Information theory states: For the same source and same distortion, (1) layered encoding requires at least as much data rate as a non-layered encoding (2) equality requires a strict Markov condition to apply to the source

13. Layering Overhead • Protocol and packetization overhead • Source of overhead: start codes, GOP information, picture header, macroblock header etc. • More severe at low data rates • According to literature, overhead can be as much as 20% ~ 30%

14. Layering Overhead - Example • Aggregate server bandwidth: 3 Mbps • Take into account the overhead (e.g. 20%), data rate contributing to video data: • CA  0.83 Mbps • CB 2.5 Mbps Group of clients (CA) – downlink: 1 Mbps Sender Group of clients (CB) – downlink: 3 Mbps Enhancement layer (2 Mbps) Base layer (1 Mbps)

15. Video Quality Degradation • Layered (2 layers with different quantizer scales) vs non-layered

16. Protocol Complexity • In layering protocols, number of channel subscriptions >= 1, which incurs • More join / leave group messages • Better synchronization capability

17. Summary • Three basic approaches to Internet heterogeneity problem • Superiority not always goes to layered multicast protocol

18. Discussion • Possible applications in multicast VoD systems • Fast-forward (FF) VCR operations • Normal playback resumption after VCR operations

19. Q & A • Thank you