Research On Proxy Caching And Stream-Scheduling Technology In Video-on-Demand System

The emergence of the Internet as a pervasive communication medium, and a mature digital video technology have made video-on-demand (VOD) services a reality. However, due to the high bandwidth requirements and the long-lived nature of digital video, server and network bandwidths are proving to be bottleneck in the widespread usage of video streaming over the Internet. This is the reason that the quality of service for clients could not be guaranteed. Therefore, it is highly important that server and network bandwidths are utilized efficiently in VOD. In this paper, we try to use less bandwidth resources to provide servicing for more access users with excellent multimedia technology strategy.The main contributions of this dissertation are organized as follows.(1) The World Wide Web system in the Internet has fully confirmed that caching technology is an important way of efficient utilization of bandwidth resources, and so has the VOD system. In particular, only video-prefix caching strategy has been confirmed being efficient and saving storage space, because digital video is huge. The analysis of media file popularity distribution reveals that it can be approximated by Zipf-like distribution. A few of media files called popular are accessed by the vast majority of users. The existing caching strategies can not separate the popular from non-popular files. How to cache all of the files was researched in order to save bandwidth resources efficiently in the case of limited storage space in this paper. An efficient proxy-caching algorithm was presented to minimize network bandwidth utilization of proxy-based distributed VOD system. A global trial technique was developed to seek optimal proxy-caching allocation for various popular videos. Combining the proxy-caching algorithm with traditional video-scheduling schemes the effects of the choice policy of cache allocation and proxy cache size on the totaltransmission cost were explored quantitatively. The caching algorithm was thus proved to be effective and practical for server design to provide on-line video allocations.In addition, video-scheduling mechanisms are also an important way of efficient utilization of bandwidth resources. An optimal non-reactive scheduling mechanism, a video-integrated scheduling mechanism and an adaptive scheduling named CMP (client multicast patching) were proposed.(2) For a few of popular videos and non-popular videos, non-reactive and reactive scheduling schemes are used, respectively. In non-reactive schemes, the server divides a video object into a number of segments and continuously broadcasts the segments on a set of transmission channels. Using a constant number of channels, the non-reactive scheme can deliver the video to an arbitrary number of clients. However, the length of the first segment determines the worst case of startup delay for any client, and in order to reduce the delay more channels would be needed. In order to improve the non-reactive scheme, a Patching-combine Segment Broadcast scheme (PSB) was proposed. The theoretic analysis of optimal channel allocation vector for videos and service delay was given with Lagrange multiplier method and G/G/M queuing model. Performance analysis shows that PSB scheme can achieve up to 50% bandwidth resource reduction under general tolerable delay. On the other hand, the delay is decreased and quality of service is improved under a bandwidth usage.(3) The research on video-scheduling started from the server-based VOD system. After proxy caching technology is developed, video-scheduling in proxy-based system is proved to be a heavy question of discussion. In the same way of server-based system, there are two existing scheduling schemes including non-reactive and reactive ones in a proxy-based VOD system. In order to utilize bandwidth resources more efficiently, a clear distinction between popular and non-popular videos was made, taking the visual consumption of system's bandwidth resources as a performance index. An integrated video-scheduling scheme was proposed to configure non-reactive scheduling and reactive scheduling schemes for popular and non-popular videos, respectively. In addition, the integrated video-scheduling scheme was combined with the previous optimal proxy caching algorithm, thus resulting in great alleviation of the bandwidth bottleneck.(4) A representative caching strategy is caching an initial prefix of the video. In...