1. Dual-Plan Bandwidth Smoothing for Layered-Encoded Video Tong Gan, Kai-Kuang Ma, and Liren Zhang IEEE Trans. Multimedia, Apr. 2005

2. Outline Bandwidth smoothing Dual-plan bandwidth smoothing (DBS) scheme Trunk plan Branch plan Simulation results

3. System architecture

4. Example of BS

5. Dual-plan bandwidth smoothing scheme Based on the renegotiated constant bit rate (RCBR) service. The reserved bandwidth limits the peak rate of the schedule. Renegotiation may fail (the reservation request for a higher bandwidth may be rejected by the network) Upon a renegotiation failure, the server has no choice but to pause the transmission. Use layered video coding to guarantee continuous video playback. L layers: one base layer and (L-1) enhancement layers. Trunk plan A L (t): deliver all L layers Branch plan A m (t): the branch plan for the m th renegotiation instance r m,j : the renegotiation instances (the j th renegotiation after the m th rate change)

6. Example: DBS scheme b1b1 b2b2 b3b3 b4b4 b5b5 Trunk plan A L (t) r 1,0 r 0,0 r 1,1 r 1,2 r 2,0 r 2,1 r 3,0 r 3,1 r 4,0 r 4,1 r 5,0 Time, t Cumulative data size, s Branch plan A 1 (t) Branch plan A 3 (t)Branch plan A 4 (t) b i = c i

7. Example: switch plan b1b1 b2b2 b3b3 Trunk plan A L (t) r 1,0 r 0,0 r 1,1 r 1,2 r 2,0 r 2,1 r 3,0 Time, t Cumulative data size, s b2b2 b3b3 Branch plan A 1 (t)

8. Procedure Compute the trunk plan Adjust renegotiation instances of the trunk plan Match frame boundaries Compute the branch plans Frame boundaries Number of layers being transmitted

9. Trunk plans Minimum Polyline Smoothing (MPS) algorithm Renegotiation instances Switching procedure only occurs at frame boundaries. If the server intends to switch to a branch plan, it must completely send out all L layers of the k th frame and then follows the branch plan to transmit the (k+1) th frame.

10. Adjust renegotiation instance (1/2) A L (t) cmcm C m+1 vmvm kmΔkmΔ V L (t) renegotiate before the rate increases

11. Adjust renegotiation instance (2/2) A L (t) cmcm C m+1 vmvm kmΔkmΔ V L (t) renegotiate after the rate decreases

12. Possible cases of A L (t)

13. Branch plans For each bandwidth increasing instance, an associated branch plan should be established. Renegotiation instances The server should switch back to the trunk plan as early as possible. However, more renegotiations imply more overhead. Use T r to control renegotiation frequency. Renegotiations should only occur at frame boundary. The branch plan continues until the end of the video, renegotiate successfully, or (the bandwidth requirement of the video) < (the current reserved bandwidth).

14. Example: computing the branch plan A m (t) r m,0 r m,1 r m,2 V L (t) A L (t) Vm(t)Vm(t) U L (t) Um(t)Um(t) Am(t)Am(t)

15. Scheme (branch plan) The server transmits an equal number of l (l ≦ L) layers of each frame. The goal: maximize l Procedure: For a given l, the corresponding constraint region is constructed. Apply MPS algorithm to compute a temporary transmission plan. If the plan satisfies the bandwidth constraint, it is saved as the branch plan; otherwise, l will be decremented and the procedure is repeated.

16. Exploit the MPS algorithm to compute A l (t) Vm(t)Vm(t) Am(t)Am(t) V l (t) Um(t)Um(t) U l (t) r_rightr_left(p-1)Δ(q-1)Δ Transmit the p th frame to the (q-1) th frame during r_left ≦ t < r_right. A l (t) Finish line Starting point G

17. Simulation C: link capacity b min, b avg, b max : the minimum, average, and maximum transmission rate of the trunk plan. K min = C / b max : the number of clients admitted when the peak-rate reservation is employed. K avg = C / b avg : the number of clients accepted when each one can transmit at the average rate. K max = C / b min : the maximum number of concurrent connections admitted. (base layer only)

18. Configurations Playback buffer B = 1 MB Minimum time gap of renegotiation interval T r = 10 sec.

19. Measurements Network utilization Enhancement layer discarding ratio Video quality degradation interval

20. Different T r (1/3) In heavy load, renegotiation failures occur frequently, limiting the number of enhancement layers to be delivered. L = 2

21. Different T r (2/3) L = 2

22. Different T r (3/3) L = 2

23. Different enhancement-layer granularities (1/3) T r = 10

24. Different enhancement-layer granularities (2/3) T r = 10

25. Different enhancement-layer granularities (3/3) Two cases are the same! T r = 10

26. Playback buffer B = 5 MB (1/3) ? better than the case B = 1MB (L=2, 65%)

27. Playback buffer B = 5 MB (2/3) better than the case B = 1MB (L=2, 60%)

28. Playback buffer B = 5 MB (3/3) better than the case B = 1MB (K max, 2000 s)

29. Summary The performance of DBS can be improved by reducing the minimum time gap of renegotiation interval T r ; employing multilayer video encoding with fine granularity; and/or increasing the playback buffer size B.