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Provision of VCR-like Functions in Multicast VoD

Provision of VCR-like Functions in Multicast VoD. Presentation Map. Introduction Problem identification Review on solutions Issues in algorithm design Q & A. Introduction. Targets Based on multicast network architecture, implement VCR-like functions

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Provision of VCR-like Functions in Multicast VoD

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  1. Provision of VCR-like Functions in Multicast VoD

  2. Presentation Map • Introduction • Problem identification • Review on solutions • Issues in algorithm design • Q & A

  3. Introduction • Targets • Based on multicast network architecture, implement VCR-like functions • Minimize additional system resources for the resultant system

  4. Unicast network Problem Identification • TVoD (True Video-on-Demand) • NVoD (Near Video-on-Demand) • Comparisons: server bandwidth, response time, play-out point control • One channel is dedicated to one client • Waiting time depends on system load • Clients have total control once they are admitted L • Adjacent multicast channels stream video data with time lag of Tr • Clients have to wait for the start of movie broadcast, max wait = Tr, mean = Tr / 2 staggered multicast channels Tr Multicast network

  5. Problem Identification • Challenge: • How to achieve both: • Bounded access latency in NVoD • Total control in TVoD with a given set of system restrictions (e.g. server bandwidth, access bandwidth) • Current solutions: • Periodic broadcasting protocols

  6. Problem Identification • What are VCR-like operations? • Pause, stop • Fast forward / backward • Slow motion • Jump forward / backward • Result change of client play-out point relative to the movie

  7. t staggered multicast channels time bp1 bp2 bp3 bp4 movie pp pp’ Problem Identification • VCR-like functions resumption • Client play-out point and server broadcasting point are out of phase • Client has to either • Be served by unicast contingency channels  bandwidth save due to multicast is lost, or • Wait for next broadcast of play-out point  the waiting time is unacceptable under normal system configurations (e.g. staggered broadcasting of 2hr movie with 25 channels, mean wait = 144s) bp server broadcasting point pp  client play-out point

  8. Solutions for Providing VCR-like Functions • Some proposed solutions • Channel merging • Pre-fetching / Buffering • Staggered broadcasting • Quality degradation • Precision reduction • Movie preview

  9. Channel Merging • Goal: to enjoy server bandwidth save by multicast by merging streams together bp client buffer pp forward VCR operation bp client buffer pp’ channel merging bp’ client buffer pp’’ Examples: patching, piggybacking etc.

  10. Patching bp tL movie pp bp client buffer pp multicast channel transient period (T = tL) contingency channel time bp’ client buffer pp’ K. A. Hua, Y. Cai and S. Sheu, "Patching: A Multicast Technique for True Video-on-Demand Services," Proc. 6th International Conference on Multimedia , Sept 1998 Page(s): 191-200.

  11. Patching • Gain: • Further reduction of response time • Multicast efficiency improvement • Simulation results: • No. of server channels: 95 vs 100 for general multicast systems (arrival rate 0.1 / s) • Blocking probability: 8% vs 13% for general multicast systems (arrival rate 0.1 / s) • Trade-off: • Access bandwidth = 2X movie rate • Client buffer (max size = Tr of movie data, for staggered broadcasting) Ho Kyun Park, Hwang Bin Ryou, “Multicast Delivery for Interactive Video-on-Demand Service,” Proc. 12th International Conference on Information Networking, 1998 Page(s): 46 -50.

  12. Patching • Variant: • Playback rate of contingency channel: SRMDRU* (Single Rate Multicast Double Rate Unicast) Bu = 2 • Transient duration halved (T = tL/2) • Requires access bandwidth of 3X movie rate • Desirable application: • Small phase offset (tL) between client play-out point and multicasting point  short patching duration Poon, W.F., Lo, K.T., Feng, J., “Design and analysis of multicast delivery to provide VCR functionality in video-on-demand systems,” 2nd International Conference on ATM, 1999, Page(s): 132 -139.7

  13. Piggybacking • Algorithm: • To merge two streams by altering display rate • Gain: • Enables stream merging without the use of contingency channels and client buffer • Trade-off: • Long merging duration (T = 10tL for r = 5%) • Requires sophisticated hardware or pre-coding to supply movie of different playback rate • Desirable application: • Small time lag (tL) between streams to be merged tL pp1 stream 1 at (1-r*) movie rate transient period (T = tL / 2r) stream 2 at (1+r) movie rate pp2 pp1 merged and share muticast r  display rate alternation ratio pp2 L. Golubchik, J. C. S. Lui, and R. R. Muntz, "Adaptive Piggybacking: A Novel Technique for Data Sharing in Video-on-Demand Storage Servers," ACM Multimedia Systems, vol.4(30), 1996 Page(s): 14-55.

  14. t bp1 bp2 bp3 bp4 buffer staggered multicast channels pp time Pre-fetching / Buffering • Algorithm: • Always keeps the pp in the middle of buffered video bp1 bp2 bp3 bp4 bp1 bp2 bp3 bp4 pp’ pp’’ Zongming Fei; Kamel, I.; Mukherjee, S.; Ammar, M.H., “Providing Interactive Functions for Staggered Multicast Near Video-on-Demand Systems,”IEEE International Conference on Multimedia Computing and Systems, Volume: 2 , 1999, Page(s): 949 -953.

  15. Pre-fetching / Buffering • Gain: • Higher probability of buffer hit  VCR operation completion • Simulation result: • 92% vs 63% for conventional buffer schemes • Trade-off: • Extra client access bandwidth requirement (max. 3X) • Large client side buffer size (3 Tr of movie data : Tr = L / Ns) • Desirable application: • Used together with periodic broadcasting

  16. L staggered multicast channels time Tr Staggered Broadcasting • Algorithm: • Gain: • An upper bound on buffer size for merging (Tr) • An upper bound on resumption waiting time (Tr, mean = Tr / 2) • Trade-off: • Wastage of server bandwidth in case of batch size = 0 (no req. arrival in a whole time slot) • Desirable application: • Medium to high arrival rate (arrival rate > 1/Tr)

  17. Quality Degradation • Algorithm: • Quality of movie playback, such as frame rate or resolution is lowered during transient period • Gain: • Lower client access bandwidth / server bandwidth requirement • Trade-off: • Lower movie quality • Sophisticated hardware or pre-coding may be required for production of the altered video stream • Desirable application: • Efficient transcoding techniques available

  18. t staggered multicast channels time Precision Reduction • Algorithm: • Restricts play-out point jumps to video broadcasting points • Gain: • No additional contingency requirement • Zero buffer requirement • Trade-off: • Resumption points after VCR-like operations are in the increment of t (e.g. 5 mins.) • Desirable application: • Little phase offset (t) between consecutive movie broadcasts  high precision bp1 bp2 bp3 bp4 bp1 bp2 bp3 bp4 movie pp pp’ pp’’ Almeroth, K.C.; Ammar, M.H., “On the Performance of a Multicast Delivery Video-on-Demand Service with Discontinuous VCR Actions, “ IEEE International Conference on Communications, Seattle, 'Gateway to Globalization', Volume: 3 , 1995, Page(s): 1631 -1635.

  19. Previewing Movie • Algorithm: • Shows preview during admission / VCR resumption downloading / waiting period • Gain: • Creates an illusion which shortens clients’ perceived waiting time • Let clients confirm the right movie selection / seek point • Trade-off: • Zero or even slightly negative bandwidth save, depending on reusability of the preview data • Desirable application: • Client is content with movie preview Wallapak Tavanapong , Kien A. Hua, James Z. Wang, “A Framework for Supporting Previewing and VCR Operations in a Low Bandwidth Environment, “, Proceedings of the fifth ACM international conference on Multimedia, November 1997

  20. Algorithm Design • Main VoD system design considerations • Quality of service • Access latency • VCR-like function resumption destination shift • Movie playback quality • FF / FB speed-up factor • STB design • Client access bandwidth • Client buffer size • Channel retrieval policy • Server design • Channel scheduling complexity • Server bandwidth

  21. Algorithm Design • Trade-offs of different techniques • Compared to an on-demand batching multicast VoD system.

  22. Algorithm Design • Different approaches work well under different system parameters • Staggered broadcasting is suitable for moderate to high request arrival rate • Real-time video transcoding necessary for ‘Quality Degradation’ approach is possible only on high-end servers

  23. Algorithm Design • We consider an adaptive & hybrid approach: • Adaptive  different combinations of algorithms utilized reacting to change in admission / VCR resumption request arrival pattern • Hybrid  different combinations of algorithms utilized depending on the initial system parameter restrictions

  24. Current Work • Current proposed system • Based on SS-VoD, uses a combination of 3 approaches • Staggered broadcasting • Batched patching • Precision reduction C.H. Lee, Y. B. Lee, “Design, Performance Analysis and Implementation of a Super-Scalar Video-on-Demand System”

  25. L static multicast channels time Tr Current Work – Staggered Broadcasting • SS-VoD architecture • Staggered broadcasting by static multicast channels • Dynamic multicast channels for admission patching and VCR-like functions resumptions • Problem: • Even a small (0.7 time per client) Prob(VCR-op) saturates the whole system (1 movie, L = 9500, 25/25 channel allocation, arrival rate: 0.1 /s) (admission wait 6.58  143.01) dynamic multicast channels

  26. Current Work – Batched Patching • Motivation: • Attempt to minimize server loading due to VCR resumptions by multicasting • Algorithm: • Admission / merging requests of the same target point are served by one single dynamic multicast channel • Result: • Able to reduce channel requirement for dynamic admission • Problem: • VCR resumption request target points are sparsely distributed in time domain, and it is impossible to form a batch merging request 1 batched merging request 1 merging request 2

  27. Current Work – Precision Reduction • Motivation: • Try to maximize VCR resumption batch size by reduction of seeking accuracy • Algorithm #1: • All VCR resumption requests fall within a window of pp +/- tw are served as a batch pp1 tw tw tw tw batching pp2 pp1’ pp2’

  28. Current Work – Precision Reduction • Algorithm #2: • Restrict clients to seek to predefined points only (chapter-based seeking) • Result: • Further reduce bandwidth requirement by batching pre-defined chapter seek points movie L

  29. Future Work • Method to further increase batch size • Investigation of applicability of transition patching (recursive patching) on current system Ying Cai , Kien A. Hua, “An efficient bandwidth-sharing technique for true video on demand systems,” Proceedings of the seventh ACM international conference on Multimedia, 1999 , Orlando, Florida, United States

  30. Q & A • Thank you

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