A reliable statistical admission control strategy for interactive video-on-demand servers with interval caching

An admission control algorithm is a key component of a video server that supports quality of service (QoS). Such an algorithm determines whether or not a new request can be admitted to the server without compromising the required performance of the in-service users. All prior admission control policies for video servers have focussed on improving the underlying storage system utilization such that a VOD server can accept more requests while satisfying the QoS requirements. In this paper, we examine admission control for an interactive video server that uses a resource sharing mechanism, called interval caching. The primary motivation of this work is to develop an efficient admission policy to optimize the server throughput with acceptable QoS. We analyze four admission control algorithms, called deterministic, predictive, statistical average, and reliable statistical admission control (RSAC), for an interactive video server and find that the proposed RSAC scheme is quite efficient compared to the other three schemes in terms of throughput and jitter. The RSAC policy attempts to optimize the disk and cache utilization while reserving a certain amount of disk bandwidth for streams that are evicted from the cache, and are likely to cause jitter due to unavailable disk space. We estimate this reserved disk bandwidth as a function of the average number of cached steams, which in turn indicates improvement in server capacity with interval caching. The average number of cached streams and the subsequent reserved bandwidth are computed wing a simple, yet accurate mathematical model. Extensive performance evaluation indicates that the RSAC is an attractive scheme for an interactive or non-interactive video server and can be implemented with other performance enhancement techniques