Scheduling Issues in Video-on-Demand Systems

The advance of high bandwidth communication technologies has created opportunites for various multimedia applications, such as video-on-demand (VOD). We consider in this chapter four types of scheduling which are required for VOD systems: viewer scheduling, stream scheduling, disk copy scheduling and disk arm scheduling. Viewer scheduling focuses on how to maximize the sharing of video streams among viewers requesting the same video. Stream scheduling involves maximizing system throughput while supporting VCR functions such as pause and resume. Disk copy scheduling determines which disks (or disk arrays) to select for videos replicated on multiple disks, minimizing disk load imbalances. Disk arm scheduling optimizes the way that disk arms are scheduled to serve multiple requests to a disk, thus maximizing the number of isochronous video streams supportable by a disk. We examine the various issues encountered in these four types of scheduling, and consider the solutions available.