Recursive Patching by Wong Ying Wai

Agenda Introduction Review on patching  Patching  Transition patching Recursive patching Stream assignment Performance optimization Summary

Introduction Video-on-Demand (VoD)  A system by which viewers can watch video programs on their own television sets or similar devices at the time they choose. TVoD  Each client is served by one video stream  Full control over video playback  Required network resources grows linearly with the number of clients NVoD  Clients are served by periodically multicasting video streams  Required network resources is independent of the number of clients  Non-zero access latency guaranteed

Introduction Some techniques involved  Batching [1] Serves several clients with one multicast stream  Patching [2] Provides immediate service to clients with low server bandwidth requirement Client’s ability to receive data from two streams simultaneously is a must  Transition patching [3] Designed based on patching Further reduces amount of server bandwidth requirement [1]A. Dan, D. Sitaram, and P. Shahabuddin, “Dynamic batching policies for an on-demand video server,” Multimedia Systems, vol. 4, no. 3, June 1996, pp [2]K. A. Hua, Y. Cai, and S. Sheu, "Patching: A multicast technique for true video-on-demand services," in Proc. 6th International Conference on Multimedia, Sep. 1998, pp [3]Y. Cai and K. A. Hua, “An efficient bandwidth-sharing technique for true video on demand systems,” in Proc. 7th ACM international conference on Multimedia, Orlando, Florida, United States, 1999.

0tbtb SaSa SbSb ScSc tctc D4D4 D5D5 D1D1 D2D2 D3D3 D6D6 D7D7 D1D1 D1D1 D2D2 D3D3 D4D4 D5D5 D1D1 D2D2 D3D3 D6D6 D7D7 D4D4 D5D5 D4D4 D5D5 D1D1 D2D2 D3D3 D6D6 D7D7 D7D7 D4D4 D5D5 D6D6 D7D7 D1D1 D2D2 D3D3 D1D1 D2D2 D3D3 D6D6 D7D7 D4D4 D5D5 D4D4 D5D5 D1D1 D2D2 D3D3 D6D6 D7D7 D4D4 D5D5 D6D6 D7D7 D1D1 D2D2 D3D3 rara rbrb rcrc Client data reception Multicasting schedule rara rbrb rcrc Client playback t c - t b 2t c - t b Phase 1Phase 2Phase 3 Illustration of patching and transition patching Patching Schemes

Resource Savings Additional server bandwidth for supporting client r c by  A new video multicast stream: LR (L:movie length, R: movie rate)  Simple patching : t c R  Transition patching: 3(t c -t b )R Example: L = 7200, t a = 0, t b = 200, t c = 250, costs by  A new video multicast stream: 7200R  Simple patching : 250R  Transition patching: 150R

Recursive Patching Basic principle of patching  Aim: To reduce the total server bandwidth requirement  By: Catching up a nearby video stream first instead of the multicast video stream  Result: The length of missing portion (the duration of the new patching stream) is reduced Applied recursively  Recursive patching (RP)

0tbtb SaSa SbSb ScSc tctc C4C4 C1C1 C2C2 C6C6 C1C1 C1C1 C2C2 C3C3 rdrd Client data reception Multicasting schedule Client playback tdtd SdSd C1C1 C2C2 C3C3 C3C3 C4C4 C5C5 C1C1 C2C2 C3C3 C4C4 C5C5 C6C6 C1C1 C2C2 C3C3 C4C4 C5C5 C6C6 rdrd C5C5 2t d - t b 2t d - t c - t b t d - t c Phase 2Phase 3Phase 4 Phase 1 Recursive Patching Illustration of recursive patching

Recursive Patching k-phase recursive patching (kP-RP)  The patching process involving totally k video streams, and consisting of k stages  2P-RP  Simple patching  3P-RP  Transition patching

Resource Savings Additional server bandwidth for supporting client r d by  A new video multicast stream: LR  Simple patching : t d R  Transition patching with S b : (3t d -2t c -t b ) R  4P-RP: 5(t d -t c ) R Example: t d = 260, costs by  A new video multicast stream: 7200R  Simple patching : 260R  Transition patching: 80R  4P-RP: 50R

r1r1 R r2r2 P r3r3 P rkrk T1T1 r k+1 P r m-1 P rprp R …… … … ω0ω0 ω1ω1 stream type r k-1 P rmrm T2T2 ω2ω2 L 0 patching group L 1 patching group ω1ω1 rqrq T1T1 ω2ω2 rnrn T2T2 r m+1 P r n-1 P … r n+1 P L 2 patching group … Stream Assignment Stream type assignment scheme

Stream Assignment Patching sequences for clients assigned  R-stream: the assigned stream  T k -stream: (k+1)P-RP  P-stream: (k+2)P-RP, where k is determined by the latest T-stream

Performance Optimization Values of ω k approximate the mean separation of T k -streams: ω k + 1/λ (λ: arrival rate) Too long  Cost of subsequent P-streams grows too high Too short  Crowded of T k -streams

Summary Recursive patching discussion Description of stream assignment scheme Briefing of performance optimization