An empirical study of admission control strategies in video servers

A video server guarantees the I/O bandwidth required for the smooth playback of a video access request once it has been admitted into the system. To ensure that new video access requests will not jeopardize the bandwidth guarantees promised to existing streams, an admission control module that decides whether a new request should be granted based on the resource usage is essential in the design of video servers. This paper presents a general framework in which video server admission control algorithms can be described in terms of how I/O delays are estimated. Then five specific admission control algorithms are studied in detail. The performances of these algorithms care analyzed in the context of an operational disk-array-based video server called SBVS. Detailed measurements from actual implementations of these admission control algorithms are used to compare their performances in terms of the maximum numbers of streams that can be admitted without causing overloads. One surprising result from this work is that the performance gap between the statistical and deterministic algorithms is between 10% to 40%, which is much smaller than were reported in earlier work