Peer-To-Peer Multimedia Streaming Using BitTorrent

1. Peer-To-Peer Multimedia Streaming Using BitTorrent Purvi Shah, Jehan-François Pâris University of HoustonHouston, TX

2. Problem Definition One Server Transferring videos is a resource intensive task! ManyCustomers • Objectives • Customer satisfaction:Minimize customer waiting time • Cost effectiveness:Reduce operational costs (mostly hardware costs)

3. Transferring Videos • Video download: • Just like any other file • Simplest case: file downloaded using conventional protocol • Playback does not overlap with the transfer • Video streaming from a server: • Playback of video starts while video is downloaded • No need to wait until download is completed • New challenge: ensuring on-time delivery of data • Otherwise the client cannot keep playing the video

4. Why use P2P Architecture? • Infrastructure-based approach(e.g. Akamai) • Most commonly used • Client-server architecture • Expensive: Huge server farms • Best effort delivery • Client upload capacity completely unutilized • Not suitable for flash crowds

5. Why use P2P Architecture? • IP Multicast • Highly efficient bandwidth usage • Several drawbacks so far • Infrastructure level changes make most administrators reluctant to provide it • Security flaws • No effective & widely accepted transport protocol on IP multicast layer

6. P2P Architecture • Leverage power of P2P networks • Multiple solutions are possible • Tree based structured overlay networks • Leaf clients’ bandwidth unutilized • Less reliable • Complex overlay construction • Content bottlenecks • Fairness issues

7. Our Solution • Mesh based unstructured overlay • Based on widely-used BitTorrent content distribution protocol • A P2P protocol started ~ 2002 • Linux distributors such as Lindows offer software updates via BT • Blizzard uses BT to distribute game patches • Start to distribute films through BT this year

9. BitTorrent (I)

10. BitTorrent (II) • Has a central tracker • Keeps information on peers • Responds to requests for that information • Service subscription • Built-in incentives: Rechoking • Give preference to cooperative peers: Tit-for-tat exchange of content chunks • Random search: Optimistic un-choke • When all chunks are downloaded, peers can reconstruct the whole file • Not tailored to streaming applications

11. Evaluation Methodology • Simulation-based • Answers depend on many parameters • Hard to control in measurements or to model • Java based discrete-event simulator • Models queuing delay and transmission delay • Remains faithful to BT specifications

12. BT Limitations • BT does not account for thereal-time needs of streaming applications • Chunk selection • Peers do not download chunks in sequence • Neighbor selection • Incentive mechanism makes too many peers to wait for too long before joining the swarm

13. Chunk Selection Policy • Replace BT rarest first policy by a sliding window policy • Forward moving window is equal to viewing delay chunk not yet received Download window missed chunk received chunk playback start playback delay

14. Two Options • Sequential policy • Peers download first the chunks at the beginning of the window • Limit the opportunity to exchange chunks between the peers • Rarest-first policy • Peers download first the chunks within the window that are least replicated among its neighbors • Feasibility of swarming by diversifying available chunks among peers

15. Best Worst

17. Discussion • Switching to a sliding window policy greatly increases quality of service • Must use a rarest first inside window policy • Change does not suffice to achieve a satisfactory quality of service

18. Neighbor Selection Policy • BT tit-for-tat policy • Peers select other peers according to their observed behaviors • Significant number of peers suffer from slow start • Randomized tit-for-tat policy • At the beginning of every playback each peer selects neighbors at random • Rapid diffusion of new chunks among peers • Gives more free tries to a larger number of peers in the swarm to download chunks

21. Discussion • Should combine our neighbor selection policy with our sliding window chunk selection policy • Can then achieve an excellent QoS with playback delays as short as 30 s as long as video consumption rate does not exceed 60 % of network link bandwidth.

22. Comparison withClient-Server Solutions

23. Chunk size selection • Small chunks • Result in faster chunk downloads • Occasion more processing overhead • Larger chunks • Cause slow starts for every sliding window • Our simulations indicate that 256KB is a good compromise

25. Premature Departures • Peer departures before the end of the session • Can be voluntary or resulting from network failures • When a peer leaves the swarm, it tears down connections to its neighbors • Each of its neighbors to lose one of their active connections

26. Can tolerate the loss ofat least 60 % of the peers

27. Future Work • Current work • On-demand streaming • Robustness • Detect malicious and selfish peers • Incorporate a trust management system into the protocol • Performance evaluation • Conduct a comparison study

28. Thank You – Questions? Contact: purvi@cs.uh.edu paris@cs.uh.edu

29. Extra slides

30. nVoD • Dynamics of client participations, i.e. churn • Clients do no synchronize their viewing times • Serve many peers even if they arrive according to different patterns

31. Admission control policy (I) • Determine if a new peer request can be accepted without violating the QoS requirements of the existing customers • Based on server oriented staggered broadcast scheme • Combine P2P streaming and staggered broadcasting ensures high QoS • Beneficial for popular videos

32. Admission control policy (II) • Use tracker to batch clients arriving close in time form a session • Closeness is determined by threshold θ • Service latency, though server oriented, is independent of number of clients • Can handle flash crowds • Dedicate η channels for each video making worst service latency, w D/η

33. Results • We use the M/D/η queuing model to estimate the effect on the playback delay experienced by the peers