1. A P2P On-Demand Video Streaming System with Multiple Description Coding Yanming Shen, Xiaofeng Xu, Shivendra Panwar, Keith Ross, Yao Wang Polytechnic University

2. Introduction  Media content forms a significant fraction of Internet traffic. -Problem: live streaming to a large audience in the wide- area Internet -Standard solution: Infrastructure-based 1. Bandwidth costs from a central source can be costly 2. Single source may not be able to provide full bandwidth  P2P streaming is attractive -Self scaling -Easy to deploy, low cost  Problem: Unreliable peers  Resilience to peer failures, departures - multiple description coding

3. System Overview  Videos are encoded into multiple descriptions.  Place each description on a different server.  When a client wants to see a video, multiple peers act as servers, each sending a different description of the video to the client.  When a server peer disconnects in the middle of a streaming session, the system searches for a replacement peer that is storing the same video description and has sufficient uplink bandwidth.

4. System Overview  Consider a star network architecture.  Initially, node 4 receives descriptions from nodes 2 and 3.  Node 5 receives from nodes 1 and 4.  Then node 2 disconnects,  And the system recovers by assigning node 6 as a replacement. While locating and establishing a replacement, visual quality at node 4 is degraded. We use a fat pipe to indicate the downlink of each node, and a thin pipe to illustrate the uplink of each node.  Generally, a node can function as a client only (e.g., node 5);  A server only (e.g., node 1);  Or simultaneously as a server and a client (e.g., node 4). Server & Client Client Server

5. Benefits of Multiple Descriptions  When a server peer disconnects, client only loses a single description  Each description has a low bit-rate.  A natural fit to current Internet access architecture: Asymmetric upstream (low) and downstream (high) bandwidths, ample bandwidth in the core Internet  Spread the load over the serving peers  Multiplexing gains in the core Internet  Prevent illegal access to the video

6. System Overview  Five interacting components of system design: 1.Video Coding; 2.Description Placement; 3.Admission Control; 4.Server Selection; 5.Description Delivery.

7. Design Criterion  Performance measures 1.Acceptance probability: the likelihood the system will locate the necessary descriptions and establish a session. 2.Video quality: the visual quality of the session, from start to finish.

8. MD-FEC Video Coding (R M -R M-1 )/M 12 R1R1 R2R2 RmRm RMRM R1R1 (R 2 -R 1 )/2 … … … … (R m -R m-1 )/m (R M -R M-1 )/M FEC(R 2 -R 1 )/2 …… (R m -R m-1 )/m FEC … … … R0R0 R1R1 R2R2 RmRm RMRM …… Distortion D0D0 D1D1 D2D2 DmDm DMDM  Divide the stream into Group Of Frames (GOF).  Each GOF is partitioned into M layers.  kth layer is further divided into k equal- length groups.  Reed-Solomon (RS) code is applied to k groups to yield M groups. … mM

9. MD-FEC Video Coding  P m denotes the probability of receiving m out of M descriptions.  D m (R 1, …,R M ) denotes the distortion when m descriptions are received for layer partition (R 1, …,R M ).  Expected distortion  The MD-FEC optimization problem can be formulated for a given M, r, and P as follows: determine the optimal layer partition (R 1, …,R M ) for

10. Simulation Setting  Video data -Video coded into scalable bit stream using the MPEG-4 FGS codec -Generate M descriptions using the MD-FEC method, M from 4 to 32. -total rate: 512 kbps or 576 kbps.  Network setting -Fixed uplink bandwidth (250 kbps) and storage (230 MBytes) -Each node alternates between “connect” and “disconnect” status.  Video placement -each node stores at most one description for a particular video.  Admission control -Parameter Q max : If the total number of sessions in the network is greater than Q max, then the new requests are blocked.

11. Simulation Results  System performance generally improves as the number of descriptions (M) for the videos increases.

12. Simulation Results  Video quality decreases as Q max increases.  A lower total rate might give a better video quality.

13. Conclusion  Peer-to-peer networking with multiple description video coding is a promising technique for an on- demand video streaming service.  Video quality can be maintained in the face of peer departures.  Increasing the number of descriptions can improve the system performance.  Future work: layered coding