Analysis of Using Broadcast and Proxy for Streaming Layered Encoded Videos Wilson, Wing-Fai Poon and Kwok-Tung Lo

Contents  Introduction  System Architecture  Analytical Model of the system  Results  Conclusions

Introduction (1)  Video-on-Demand system has not been commercial success  Two directions to provide a cost-effective VoD services: r Multicast/broadcast techniques to share the system resources r Proxy servers to minimize the network transmission cost  Multicast/broadcast r Near VoD: Skyscraper, Fast Data, Poly-harmonic r True (zero-delay) VoD: Patching, Stream Tapping

Introduction (2)  Proxy r If the proxy is congested or the requested video is not stored in it, the customer will be served by the central server r Proxy pre-caches a portion/whole of a video to serve the local customers r There is a trade-off between the limited backbone bandwidth and the cost of the local storage

Heterogeneous Environment  Improve the system performance under the homogeneous environment  Heterogeneous environment r Use the layered video streams r Flexibly provide different quality of videos by transmitting different number of layers according to the available bandwidth between the server and customers

Objective  Build a large-scale VoD system in heterogeneous network environment  Explore hierarchical network architecture to provide VoD services  Evaluate the system performance if the network has multicast/broadcast capability  Videos are layered encoded r store in the proxy server r broadcast to the customers

System Architecture Central Repository Wide Area Network Proxy Server Local Area 56 kbps Clients Video data Local Area 1.5Mbps Clients 3 Mbps Clients low quality videos high quality videos Local Area

 r j is the probability of customers requesting the j th quality of the videos  The lower quality layers must be first stored before caching the enhancement layer r q mj as the fraction of customers requesting the j th layer of video m Proxy Server  b mj as the proxy map to describe the subsets of video layers in proxy  set to 1 if layer j of video m is in proxy; otherwise, set to 0

Proxy Server Maximize: Subject to where

System Model  Requests go up to the central server can be found  Average bandwidth requirement for a video request is equal to where

System Model  Model as M/M/N/N queuing system  If B is the available bandwidth between the server and the proxy, the number of channels is  The service rate of the system is where T is the mean service time  P I : percentage of new requests blocked from the central server where

System Model  Proxy server can support some of these customers with lower quality of video streams  P II : proportion of new requests completely blocked from the system

Multicast/Broadcast  The proxy is not be able to serve the video requests  Layers of the videos can be broadcast over the backbone channels r For example, a customer may receive the base layer of a video from the broadcast channel and the enhancement layers from the dedicated channels r The customer thus at least receives the basic quality of the video even if the network is very congested

Multicast/Broadcast Layer 4 Layer 3 Layer 1 Layer 2 client1client2 Proxy server Central server Network Broadcasting channels

Multicast/Broadcast  D x as the number of channels required for the broadcasting protocol x  g m as the highest layer of video m using the broadcasting scheme r j th layer of video m, where, is either broadcast to the customers or stored in the proxy  Bandwidth requirement for broadcasting  g m can be calculated such that

System Model  The arrival rate for the dedicated channels can be reduced because some video layers are being broadcast  The average streaming rate of the dedicated channels is equal to  M/M/N * /N * queue can be applied to calculate the blocking probability of the system

System Model where

Simulation  Simulation Model r client requests are modeled as the Poisson arrival process r video popularity is followed by Zipf’s distribution  Three scenarios of requesting quality pattern r Scenario A (S-A): r 5 = 1, r 1 = r 3 = r 4 = r 2 = 0 r Scenario B (S-B): r 2 = r 5 = 0.5, r 1 = r 3 = r 4 = 0 r Scenario C (S-C): r 1 = r 2 = r 3 = r 4 = r 5 = 0.2

Results (1) Number of videos: 200 Video Length: 90 min Proxy Size: 10 videos Bandwidth: 100Mbps

Results (2) Number of videos: 200 Video Length: 90 min Arrival Rate: 0.3/s Bandwidth: 100Mbps

Results (3) Number of videos: 200 Video Length: 90 min Proxy Size: 10 videos Bandwidth: 100Mbps Broadcast: 10 channels

Results (4) Number of videos: 200 Video Length: 90 min Arrival Rate: 0.5 or 1.0/s Proxy Size: 5 or 10 videos

Results (5) Number of videos: 200 Video Length: 90 min Proxy Size: 5 videos Broadcast: 10 channels

Result (6) Number of videos: 200 Video Length: 90 min Arrival Rate: 0.5 or 1.0/s Proxy Size: 5 or 10 videos Broadcast: 10 channels

Conclusion  One of the challenges to provide VoD service is how the video streams can be delivered in the heterogeneous environment  Scalability r hierarchical architecture r efficient broadcasting protocols  Heterogeneous r Layered encoded videos  Bandwidth reserved for broadcasting?  Caching policy if proxies can communicate with each other?