Patching

Until now, true video-on-demand can only be achieved using a dedicated data flow for each sen-ice request. This brute- force approach is prohibitively expensive. Using multicast can significantly reduce the system cost. This solution, however, must delay services in order to serve many requests as a batch. In this paper, we consider a third alternative called Patching. In our technique, an existing multicast can expand dynamically to serve new clients. Allowing new clients to join an existing multicast improves the efficiency of the multicast. Furthermore, since all requests can be served im-mediately, the clients experience no service delay and true video-on-demand can be achieved. A significant contribution of this work, is making multicast work for true video- on-demand services. In feet, we are able to eliminate the service latency and improve the efficiency of multicast at the same time. To assess the benefit of this scheme, we perform simulations to compare its performance with that of standard multicast. Our simulation results indicate convincingly that- Patching offers substantially better performance. © 1998 ACM.