Dimensioning the capacity of true video-on-demand servers

The need to reduce the huge bandwidth demand of video-on-demand (VoD) services has led to the conception of both multicast and broadcast based techniques for the deployment of such services on a large scale. Interactivity, a desirable feature for video services, includes the capacity to perform VCR operations. However, whenever a viewer requests the performance of a VCR operation, his/her video stream becomes unsynchronized with that of his/her multicast group, and a new channel must be allocated for the performance of this operation. The present paper introduces a novel approach for determining the number of video channels needed to support such interactivity. Moreover, it investigates the performance of interactive systems with a pool of channels reserved for the support of VCR operations. Systems with both batching and piggybacking are analyzed. Results indicate that for a medium to high number of users performing VCR operations the number of channels required to achieve target levels of quality-of-service is lower for systems with no pool of reserved channels than it is for systems with such a pool.