Scalable video distribution techniques

1. PLANETE project presentation: Scalable video distribution techniques Laurentiu Barza Sophia Antipolis 12 October 2000

2. Motivation • User behaviour: • skewed access: Zipf Rule 20/80 • desire rapid access • may be willing to sacrifice access time and some interactivity for lower cost service • Goal: scalable service that provides almost « true VoD » at a much lower cost

3. Outline Basic schemes: • Server-Push Broadcast - Baseline - DeBey - Pyramid & Skyscraper - Tailor-Made • Client-Pull with Multicast - Batching

4. Baseline Broadcast Scheme • Continuos multicast of hot videos • M videos • K channels • assign K/M channels to each video • schedule video start times • « pay-per-view » model

5. Baseline Broadcast Length of Movie 3 channels/movie

6. DeBey Broadcast • Split a video into N equal sized segments • Segment “m” is transmitted ONCE every “m” time • reduce the mean transmission rate • peak transmission rate very high

7. De Bey Broadcast Channels 1 1 1 1 1 1 1 1 1 ... 2 2 2 2 2 ... 3 3 3 ... Time t0 t1 t2 t3 t4

8. Pyramid broadcasting • Split video into N segments of lengths L1,L2,…,Ln • L = L1+L2+…+Ln • Segment size: Li =  * Li+1 • lower max access time than baseline scheme • the client has to listen 2 channels simultaneous • significant receiver buffering: up to 70% of video length

9. Pyramid Segmentation Skyscraper segmentation

10. Skyscraper Broadcasting • use relative segment size progression: 1, 2, 2, 5, 5, 12, 12, 25, 25, 52, 52… • requires less buffering than pyramid scheme • requires strict synchronization among the multicast channels

11. Tailor-Made approach • Cover all possible design dimensions • server transmission rate • start-up latency • peak client recording rate • peak client storage requirements • Is a modification of de Bey: • all the segments have the same length but are transmitted continuously

12. Taylor-Made Approach Channels 1 1 1 1 1 1 1 1 1 ... 2 2 2 2 2 ... ... 3 3 3 ... 4 4 Time t0 t1 t2 t3 t4

13. Taylor-Made Approach Channels Client joins 1 1 1 1 1 1 1 1 1 ... 2 2 2 2 2 ... ... 3 3 3 ... 4 4 Time t0 t1 t2 t3 t4

14. Partial conclusion Proposed schemes characteristics: • are server-push approach • are designed for hot video • vary the way they segment a video • trade-off server transmission rate, client IO bandwidth and client storage and recording requirements • have all non-zero start-up latency

15. Client-pull: Batching • delay request for a video until a certain number of requests for that video arrive before the video is delivered • batching is only effective for popular videos • reduce server and network resource requirements • start-up latency can be very high • popularity of required video • no. Of requests required to schedule a video

16. Controlled multicast • Controlled Multicast = Batching + Optimal Patching • define a patch threshold that trades off the size of the patches and the frequency in which new multicast channels are initiated

17. Catching • Server broadcast video via dedicated multicast channels • Client • immediately joins the appropriate multicast channel • requests to the server the missing first part of the video • Server sends the first part to the client via a dedicated unicast channel

18. Multicast with caching (Mcache) • Server multicasts body of a video using • object channels: multicast the body of the video • patch channels: multicast parts of the video right after the prefix • Client initiates two parallel requests • the prefix from the cache • video body from the server • Server:calculates schedule and inform client which channel and when to join

19. Conclusion Various schemes for scalable video distribution • Concern only hot and popular video • Emulate the native Video on Demand service while requiring much less ressources at the server • Server Push vs. Client Pull models • Zero latency vs. Non-zero latency schemes

21. patched Prefix(cached) Body(server)