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P2VoD: Providing Fault Tolerant Video-on-Demand Streaming in Peer-to-Peer Environment

P2VoD: Providing Fault Tolerant Video-on-Demand Streaming in Peer-to-Peer Environment. Tai T.Do, Kien A. Hua, Mounir A. Tantaoui Proc. of the IEEE Int. Conf. on Communications (ICC 2004). Outline. Introduction Related Work Architecture of P2VoD Performance Evaluation Conclusion.

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P2VoD: Providing Fault Tolerant Video-on-Demand Streaming in Peer-to-Peer Environment

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  1. P2VoD: Providing Fault Tolerant Video-on-Demand Streaming in Peer-to-Peer Environment Tai T.Do, Kien A. Hua, Mounir A. Tantaoui Proc. of the IEEE Int. Conf. on Communications (ICC 2004)

  2. Outline • Introduction • Related Work • Architecture of P2VoD • Performance Evaluation • Conclusion

  3. Introduction • P2P approach can potentially solve many serious problems posed in existing streaming systems • Infeasibility of IP Multicast • Network bottleneck at the video server • Several projects on “live streaming” • Not trivial to apply these techniques into VoD systems

  4. Introduction (cont.) • Live streaming • Shorter end-to-end delay, more lively the stream • Short tree rooted at the video server • User simply joins an on-going live streaming session • User may not quit if QoS degrades • VoD streaming • Liveness is irrelevant, video is pre-recorded • Whole video must be delivered • User will stop watching if QoS degrades

  5. Introduction (cont.) • Proposed techniques not based on any existing live streaming systems • Problems to be solved for a P2P VoD streaming system • Fast and localized failure recovery without jitter • Quick join • Effective handling of clients’ asynchronous requests • Small control overhead • P2VoD (Peer-to-Peer approach for VoD streaming)

  6. Related Work: P2Cast • Architecture uses a P2P approach to stream video using patching • Build application level multicast tree • Server streams the entire video over base tree • P2Cast clients provide two functions • Base stream forwarding • Patch serving • Base tree construction & patch server selection algorithm • Best Fit (BF): find the “fattest pipes” to requesting clients • BF-delay: also use network delay information • BF-delay-approx: not using actual available bandwidth, (1 or 0 represents enough bandwidth or not)

  7. Architecture of P2VoD • A streaming connection is assumed to constant bit-rate • equals to the playback rate of the video • Retrieval block (R-block) as a data unit of the video • equivalent to one unit of playback time • Each client has a buffer, whose maximum size is worth of MB units of playback time (i.e. MB R-block)

  8. Architecture of P2VoD (cont.) • abX : actual amount of buffer storage used by a client X • 1 ≤ abX ≤ MB • By using the cache, early arriving client can serve late coming clients by forwarding the stream • tjX : the joining time of a client X • X can serve clients whose joining time • [tjX, tjX+ abX]

  9. P2VoD system • abC1 = MB = 5, abC4 = 3 < MB • When C6 arrives to the system at time 3, the first R-block of the video is still in the buffer of C1 • C1 can serve the video stream to C6

  10. Architecture of P2VoD (cont.) • “Generation” • Group of clients having the same smallest numbered R-block in their caches • Generations are also numbered • G1 as the oldest generation to Gn as the youngest generation • Clients in these generations, excluding the server, form a video session • A video session is closed • none of the clients has the first R-block of the video

  11. P2VoD system • C1, C2 , C3 , C4 , and C5 all have the same smallest number R-block

  12. Data Caching and Generation (cont.) • Rules to build generations • Generations are indexed by numbers starting from 1 • Members of a lower indexed generation arrive to the system no latter than any member of other higher indexed generations • A peer in generation i-th (i > 1) receives the video stream from a peer in generation (i – 1)-th • Peers at the first generation receive the video stream directly from the server • When joining a video session of the system, a new peer • belongs to the current highest numbered generation, OR • be the first member of a newly created generation of that video session

  13. E.g. abC2 = abC1 – (tjC2 – tjC1) = 5 – (1 - 0) = 4 Data Caching and Generation (cont.) • Caching scheme with the generation concept • X and Y join the same generation at time tjXand tjY • Caching Rule: The difference of actual cache sizes used by two peers in the same generation must offset the difference in their arrival times • abX – abY = tjY – tjX

  14. Data Caching and Generation (cont.) • Assume that at time 36, peer C3 fails. • C1, C2, C4, C5 available to C8 • allow a quick and localized recovery for C8

  15. X sends control information < addX, G(X), > to server when joining the system • : expiration time when the first R-block of the video is no longer in the cache of X Control Protocol • Control Protocol is required to maintain the system connectivity • Neighbors of peer X • Siblings (peer in same G): need to keep a list of their IP addresses • Periodically update the list • Update the list on-demand (joining/leaving) • Child: agree to forward the video stream, X needs to send the IP addresses of X and its siblings to its child • Parent: first join the system, X sends the IP address to its parent

  16. Join Algorithm • Server S has the list of peers at the youngest generation for each video session, denoted as Gy • Expiration time is the same for every member of the youngest generation • Initially, when the system is empty • is set to minus infinity • Set of youngest generation peers contains only S

  17. Join Algorithm (cont.) • Case 1 • If all of the existing video sessions are closed, X will be admitted if server S still has enough outbound-bandwidth • Otherwise, X will be rejected • Case 2 • For the case where there is at least one existing video session still open, X will try to join that video session

  18. Join Algorithm (cont.) • Case 2 proceeds as follows. • Step1 • X contacts a random member of the Gy set • acquires the list of peers at the super generation of Gy. • Step2: • If texp at the super generation > tjX, then go to Step3 • Otherwise go to Step4 • Step3: (generation not expired) • X selects a parent from the super generation • If such a candidate exists, X becomes a member of Gy • X starts receiving the video stream from its selected parent • X sets its actual cache size abX to conform to the caching rule • Otherwise go to Step4

  19. Join Algorithm (cont.) • Case 2 proceeds as follows. • Step4: (generation expired) • A new generation is formed below Gy • X becomes the first member of that generation • Actual cache size abX is set to equal to MB • X selects a peer from Gy as its parent • If no such peer exists, X tries other open video sessions or contacts the server

  20. Parent Selection Criteria • Round Robin Selection • promote the fairness among peers • the requesting peer should select a peer, who hasn’t served any client for the longest period of time • Smallest Delay Selection • minimize the joining time of the requesting peer • the requesting peer picks the first peer in the candidate group, who has enough out-bound bandwidth • Smallest Distance Selection • reduce the number of links involved in the underlying network • the requesting peer chooses a peer, who has enough out-bound bandwidth and closest to it

  21. Failure Recovery • P2VoD uses a two-phase failure recovery protocol • 1) Detecting failure • Grateful failures: When a peer leaves the system, it forwards the LEAVE_MESSAGE to its children • Unexpected failures: it happens unexpectedly without any explicit warning, peers in P2VoD are required to monitor their incoming traffic

  22. Failure Recovery (cont.) • 2) Recovering from failures • Failure at a peer X, the whole sub-tree under X is affected • The rest of the sub-tree are informed to wait through the WAIT msg • A disrupted peer X finds a new parent • X contacts the siblings of its parent • If no such parent exists, X contacts the server • Otherwise, X is rejected • X succeeds, the sub-tree is recovered • X fails, the immediate children of X will invoke the recovery process

  23. Performance Evaluation • Examine the effects of two parameters in P2VoD: • max number of clients allowed in the first generation of each video session, K • max buffer size each client can use, MB • Compare P2VoD with P2Cast • Network topology using GT-ITM • Clients arriving to system follow the Poisson distribution • one Transit network (with 4 nodes) • 12 stub domains (with 96 nodes) • backbone link support 25 streams • edge link support 7 concurrent streams

  24. Performance Evaluation (cont.) • Rejection probability • probability that a client tries to join the system but can not get the service • Server stress • amount of bandwidth used at the server, or the number of streams established at the server • Number of contacts during the recovery • number of nodes a client has to contact during the recovery process

  25. Rejection probability for various maximum buffer sizes (K = 3) • MB is varied from 0.1 to 0.4 of the length of the video • When doubling size of MB, the rejection probability is reduced by half

  26. Server stress with various values of K (MB = 0.1) • In light workload, almost every clients get the video stream directly from the server • In heavy workload, most clients get the video stream from some other client, not the server • With small K, a failure at the first generation will likely cause disruption the whole video session • With large K, such failure only cause a portion of the video session to be in recovery mode

  27. P2VoD vs. P2Cast: Client rejection probability • P2VoD use K =6 & MB = 0.2 • The threshold for P2Cast is set at 0.2. • P2VoD outperforms BF because P2Cast requires each client to obtain two streams

  28. P2VoD vs. P2Cast: Server stress • In P2VoD, a video session is open as long as clients in the Gy still have the first block of the video buffer • In P2Cast, a video session is open for a short period of time starting when the first client join the video session and last for the length of the threshold

  29. P2VoD vs. P2Cast: Failure overhead • Clients arrive to the system at a rate of 0.4 per second during a period of 2 hours (3516 clients) • When the failure probability increases, the number of clients contacted during a recovery decreases • more clients leave the system, network bandwidth is also released • easier for an affected client to find a new parent

  30. Conclusion • P2VoD, a new system for Video-On-Demand streaming in a Peer-to-Peer environment • the concept of generation and caching scheme to deal effectively with failures • An efficient control protocol help P2VoD to allow clients join the system fast, as well as to recover failures in a quick and localized manner • Simulation-based performance study shows that P2VoD is superior than P2Cast

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