1. Server-Based Smoothing of Variable Bit-Rate Streams Stergios V. Anastasiadis, Kenneth C. Sevcik, and Michael Stumm ACM Multimedia 2001

2. Basics Variable-bit-rate (VBR) Higher quality. Combine video, audio, and text sources in a stream. Smoothing Reduce network requirements without degradation in video quality.

3. Overview Server Client Buffer Server Decoder Unsmoothed Smoothed

4. Transmission schedules

5. Majorize X=[x 1, …, x n ] and Y=[y 1, …, y n ] Let x [1], …, x [n] and y [1], …, y [n] denote the nonincreasing orders of X and Y. X is said to be majorized (more smooth) by Y if Ex: [4 4 2] is majorized by [8 1 1]

6. Design of the algorithm Piecewise-CBR transmission schedule Policies Consider CBR transmission segments which are as long as possible. Change the rate as early as possible. the rate change is as small as possible.

7. Algorithm B(t) D(t)

8. Server-based smoothing (1/2) Smooth disk transfers of VBR streams. Address disk bandwidth and not network utilization. The server buffer can be shared by each request.

9. Server-based smoothing (2/2) Server Client Original Disk Client Buffer Smoothed

10. System architecture Server push model Data transfers occur in rounds of fixed duration T round. The amount of stream data is determined by the decoding frame rate the resource management policy Stride-based disk space allocation Lager than the maximum stream request size per disk during a round. At most two partial stride accesses will be required to serve the request of a round on each disk.

11. Scheduling procedure Smoothing out disk bandwidth peaks by prefetching stream data into server buffers. Prefetch blocks in round i to previous round j when The disk bandwidth requirement in round j does not exceed the original disk bandwidth requirement of round i. (smooth) Server buffer required in round j up to i-1 after prefetching does not exceed the disk bandwidth required in round i. (heuristic, control free buffer)

12. Example (1/2) t013ii-1 In this algorithm, prefetching the last block to the first round is possible. But is it reasonable?

13. Example (2/2) t013ii-1 I think this approach is more reasonable!! …

14. Video streams

15. Buffer space (used)

16. Number of streams

17. Number of streams (different contents)

18. Disk time requirements

19. Server buffer requirement 64 MB is enough!!