Virtual Batching: A New Scheduling Technique for Video-on-Demand Servers

In a video-on-demand (VOD) environment, batch-ing of requests is often applied to reduce the I/O demand and increase the availability of VOD services. This scheme, however, unfairly forces rst comers to wait for subscribers arriving late at the batch. Some of these victims may become impatient and decide to renege. To address this issue, we introduce a chaining technique which allows a client station being served to forward its video data to other client stations, which requested the same video, at a slightly later time. The forwarding of data is done using the same store-and-forward mechanism of the multicast facility used in batching. With this new feature, requests arriving at a chain can be served immediately; yet they are allowed to share a single video stream. Thus, chaining enjoys the beneet of batching without its side eeect of causing long access latencies. By combining batching and chaining , we also design a scheme called Virtual Batch-ing. It extends the standard chaining mechanism to allow a client station on a chain to multicast video data to other client stations which are admitted as a batch. Our simulation results indicate that this hybrid approach ooers signiicant performance improvement.