RANI NALAMARU DEPARTMENT OF COMPUTER SCIENCE BALL STATE UNIVERSITY

1. RANI NALAMARU DEPARTMENT OF COMPUTER SCIENCE BALL STATE UNIVERSITY Efficient Transmission of Stored Video for Improved Management of Network Bandwidth

2. Overview of presentation • Introduction • Background • Problem Statement • The New VP Algorithm • Evaluation of OBA, Optimal and VP Algorithms • Summary and Future work

3. Client Video Server Client Introduction Network video • Many emerging applications • Entertainment, Distance learning, Catalogue browsing etc. Storage Network Video packet

4. Introduction Networking challenges for video • Huge bandwidth requirement if no compression • With compression traffic is bursty • Bursty traffic complicates network management Goal: Efficient transmission of high quality stored streaming video

5. Introduction Video compression and burstiness • Burstiness can occur due to: • Type of frames used in encoding • Background changes or changes in scene content Frame sizes of a stored video

6. Server Client Read video frames from disk Decode and display of frames Implement the transmission plan Buffering of frames in client buffer Transmission of frames to network Receive frames from network Start End Bandwidth Background Transmission plan • Pre-calculated schedule to transmit a video file • Mechanism to smooth the bandwidth requirement Network

7. Background Work-ahead smoothing • Have all video frames in advance • Knowledge of frame sizes Given the parameters : • Frame sizes for n frames • Client buffer size b Constraints at the client buffer • Avoid buffer underflow • Avoid buffer overflow Goal: Find a transmission plans with minimum number of rate changes and minimized sum of rate variation

8. Background • Optimal Bandwidth Allocation (OBA) algorithm (1995) • Developed by Feng, Jahanian, and Sechrest (Univ. of Michigan) • Goal of OBA algorithm is to develop a transmission plan with • smallest peak bandwidth • largest minimum bandwidth • fewest possible changes in bandwidth (rate changes)

9. Background • Optimal algorithm (1996) • Developed by Salehi, Kurose, and Towsley (Univ. of Mass.) • Goal of Optimal algorithm was to develop a transmission plan with • smallest peak bandwidth • least variation between bandwidth changes (rate variation)

10. Problem Statement • Problems with existing algorithms • Buffer sizes in the range of 20-30Mbytes are required • Retains the VBR property of stored video • Time complexity is of the order of O(NlogN) and O(N 2) • N is the number of frames

11. Problem Statement • Possibility of improvement • When to change transmission rate ? We wish to use best of both

12. c b a Visibility Polygon (VP) Algorithm • Solution - VP algorithm • Develop an algorithm based on visibility concept • Developed by Subhash Suri ( John Hopkins, 1986) • What is visibility ? • Set of points that are visible from a given point in a region visible to a not visible to a

13. Visibility Polygon (VP) Algorithm Steps in VP algorithm 1) Given frame sizes and client buffer size b. We construct the feasible region P.

14. Visibility Polygon (VP) Algorithm Steps in VP algorithm 2) Triangulate the feasible region P, let T represent the triangulation of P.

15. Visibility Polygon (VP) Algorithm Steps in VP algorithm 3) Construct the dual graph G of triangulated polygon.

16. Visibility Polygon (VP) Algorithm Steps in VP algorithm 4) Identify the shortest path from first frame to last frame. 5) Compute the windows, from which transmission plan is obtained.

17. Visibility Polygon (VP) Algorithm • Complexity of VP algorithm • Triangulation ------------------------------------ O(N) • Dual Graph Construction ---------------------------- O(N) • Breadth First Search ------------------------------- O(N) • Visibility Polygon & Windows computation ------ • Hence VP algorithm takes linear time An improvement over the previous algorithms which are O(N logN) and O(N2)

18. Evaluation • Comparison of OBA, Optimal and VP Algorithms • Simulation model • Use trace files of representative videos • Parameters for evaluation • Peak-rate bandwidth • Number of rate changes • Variation between rate changes • Time complexity

19. Evaluation Peak-rate bandwidth Peak-rate bandwidth

20. Evaluation Rate changes and variation between rate change Intervals Variation

21. Evaluation • Time complexity • Measure the number of seconds for calculating transmission plan

22. Java Simulation Program Video frames retrieved from server storage Transmission plan Evaluation Experimental setup

23. Evaluation Validation of simulation model Conservative results

24. Evaluation • Inputs • Videos were selected to be representative with respect to length and subject material

25. 8 % OBA Optimal 3.7 % Evaluation Peak-rate bandwidth

26. 19 % OBA Optimal 8.3 % Evaluation Number of rate changes

27. 15.3 % OBA Optimal 9.6 % Evaluation Amount of variation

28. 73.6 % OBA 3.8 % Optimal Evaluation Time complexity

29. If other algorithms are used Video Server Clients Evaluation What does all this mean to end users ? If VP algorithms is used

30. Summary and future work • Summary • Problems with efficiently transmitting stored (compression) video • Reviewed OBA and Optimal algorithms • New VP algorithm proposed • Simulation results showed VP algorithm has better performance to its predecessors

31. Summary and future work • Future work • To implement VP algorithm on an actual video server • To study issues of multicast support of VP algorithm