1. A Peer-to-Peer On-Demand Streaming Service and Its Performance Evaluation Yang Guo, Kyoungwon Suh, Jim Kurose, Don Towsley University of Massachusetts, Amherst, ICME 2003

2. Outline Introduction DirectStream Peer-to-Peer Overlay Node Join and Departure QoS Parent Selection Algorithm Performance Evaluation Average Server Stress Non-cooperative Clients Simulation Result

3. Introduction A VOD system can be classified as: Unicast – traditional client-server model cons: system load, client resource waste IP Multicast – under-layer multicast Change protocol and add function to routers. cons: complication, deployment, maintenance Application-layer Multicast issues: delay, trade-off between system load and client quality

4. DirectStream Peer-to-Peer Overlay DirectStream: A directory-based peer-to-peer video streaming system. Components: Content server Client with data cache buffer Directory server Maintain information about: - content server: IP address - client i: (a i, t i, τ i, b i ) = (addr, arrival time, pos, buffer length)

5. Node Join and Departure Server Directory Server {C 1, C 2, …}

6. QoS Parent Selection Algorithm Each new request gets a candidates list {c 1, c 2, …, c n } from the directory server. Select policy: 1) Low delay Number of hops between, denote n i, to be small. 2) Probability of bandwidth supplier Available bandwidth x i to be large.

7. Performance Evaluation (Workload) Average Server Stress λ: arrival rate (requests/unit time) b: buffer size (buffer time) L: video length (playback time) ρ: effective buffer size, ρ=b/L (percentage) W: normalized workload, W=λL (requests) S: server stress, the avg. workload placed at the content server

8. Performance Evaluation (cont.) Assume request arrival process is Poisson: Average server stress: E[S]=We -ρW, reach a maximum of (ep) -1 when W=1/ρ.

9. Non-cooperative Clients Freeloader A client that receives the stream and refuses to serve other clients. Greedy client A client connects directly to the server whenever possible. With freeloader probability p: Average server stress: E[S]=We (1-p)ρW, reach a maximum of 1/(eρ(1-p)) when W=1/(1-p)ρ. ex: p=0.5  maximum twice

10. Simulation Settings Network topology generated by GT-ITM: 100 nodes, each node represent a local network Core link: can support up to 10 streams Edge link: can support up to 3 streams L=100 min., one video Request arrival process: Poisson QoS parent selection parameter: r=0.5, i.e.

11. Client Rejection Probability

12. Effect of Freeloaders

13. Effect of Greedy Clients

14. Thank You!