An Active Buffer Management Technique for Providing Interactive Functions in Broadcast Video-on-Demand Systems Zongming Fei, Member, IEEE, Mostafa H. Ammar, Fellow, IEEE, Ibrahim Kamel, Member, IEEE, and Sarit Mukherjee, Member, IEEE IEEE TRANSACTIONS ON MULTIMEDIA, VOL. 7, NO. 5, OCTOBER 2005

Outline Introduction Background and related work The idea of Active Buffer Management Providing VCR functions in partitioned video broadcast Simulation results Conclusion

Introduction(1/2) Multicast VoD service  On-demand batching  Continuous broadcast Goal:  Provide interactive functions in broadcast VoD system

Introduction(2/2) Problem:  Provide VCR functions  Discontinuity of playback Solution:  Selectively prefetch segments from broadcast channels  Feasible points to adjust client’s destination

Outline Introduction Background and related work The idea of Active Buffer Management Providing VCR functions in partitioned video broadcast Simulation results Conclusion

Partitioned video broadcast  Divide video into segments  Uses one channel to send each segment in cycles  More channel, less startup latency Let bandwidth=B Mbit/s Bandwidth of each channel=b Mbit/s Channel number K=

Weight function Divide video of length L into K segments Let channel i periodically broadcast segment i (1 ≤ i ≤ K) Each segment size is determined by weight function Size of segment i is

Weight function Goal : minimize startup latency  Make increase as fast as possible  Can’t be too fast : continuity problem ! Skyscraper broadcasting scheme:  Series generated by : 1,2,2,5,5,12,12,25,25…  Upper bound W : ser to W if > W Analyze the problems encountered while try to provide interactive functions in these schemes Design new broadcasting series more suitable

VCR Actions Jump Forward/Backward (JF/JB): Fast Forward/Backward (FF/FB): Slow Forward/Backward (SF/SB): Pause: Play/Play Backward:

Outline Introduction Background and related work The idea of Active Buffer Management Providing VCR functions in partitioned video broadcast Simulation results Conclusion

Effect of VCR actions

Conventional Client Buffer Scheme Problems  Lack of flexibility for providing interactive functions  Consecutive VCR actions in the same direction may made the play point ultimately move to boundary

Active buffer manager Keep the play point in the middle of the buffer  Lower probability that VCR actions will move the play point outside the buffer Buffer manager  Adjust the content of the buffer after VCR action  Selectively download segments from broadcast channel

Active buffer manager the client buffer hold 3 segments Case 1: No VCR actions K+3 K K+2 K+1 Play point download Downloa d finish discard

Active buffer manager Case 2: Fast forward K K+2 K+1 Play point K+3 download Downloa d finish K+4 discard

Destination Adjustment for VCR Actions Client can resume normal play after VCR actions There is always destination point ouside client buffer  Adjust the destination point to feasible point

Outline Introduction Background and related work The idea of Active Buffer Management Providing VCR functions in partitioned video broadcast Simulation results Conclusion

A VCR-Oriented Broadcasting Series Segment size =1,2,4,4,8,16,16,32,64,64, Let the series increase as fast as possble Set parameter to limit the maximum number of the series

VCR function implementation with active buffer management scheme Client required 3 buffers with the same size as the maximum segment 3 loaders download from 3 channels Two components to work with VCR functions  Player : accept user interaction commands  loader/buffer manager: decide which channel the client can download segments

player Accept VCR command  Check whether the content is in the buffer  Check whether the destination point is feasible Assume current play point in segment k  Pyramid phase K, k+1,k+2 should allocate loader  Equal segment phase K-1, k,k+1 should allocate loader

loader/buffer manager Allocate loader/buffers to channel Pyramid phase  Allocate loader to segments K+1,k+2,k+3 Equal segment phase  Play point in the early half Allocate loader to segments K-1,k,k+1  Play point in the later half Allocate loader to segments K,k+1,k+2 More loader/buffer is feasible Key problem: select a appropriate channel to download required segments

Feasible point Deal with discontinuity problem Definition:  : start postion of segment i  : end postion of segment i  : broadcasting point of channel i  : represent video between two y1, y2 The segment contains destination point d is called Target segment Consider some rule for feasible point

Feasible point: case 1 If is in the buffer, then is feasible.

case 2.1: If and are in the buffer, then d is feasible. case 2.2: If are in the buffer, then is feasible. Feasible point: case 2

Feasible point: case 3

Consider the case destination pointd is after the channel point Cj  designate next segment as target segment

Outline Introduction Background and related work The idea of Active Buffer Management Providing VCR functions in partitioned video broadcast Simulation results Conclusion

Experiment settings Video length :120 min Divide the video into 30 segments for 30 channels to broadcasting First 8 segments are unequal size,the others are in equal size First segment is 4.83sec,the largest segment is 5.15min Buffer size is 3 times the largest segment

User interaction model

Experiment Definition(1/2) Pi :probablity of issuing specific VCR actions Reduce parameters:Set p7=p8=p9=0 Let,and we have Let for 1≤ i ≤6 Define as duration ratio Experiment in two ways  Change probability : we let =0.5 and vary from 0.1 to 0.9.  Change duration ratio. : we change the duration ratio from 0.2 to 1.0.

Experiment Definition(2/2) Percentage of VCR actions:  The higher this percentage, the better interactive performance of the system Percentage of destination shift:  The smaller this percentage, the better performance of the system.

Numerical Results

Outline Introduction Background and related work The idea of Active Buffer Management Providing VCR functions in partitioned video broadcast Simulation results Conclusion

A VCR-Friendly broadcast series Active buffer management technique  Provide functionality of interactive services in broadcast VoD systems. The scheme can implement VCR actions through buffering with high interaction levels.