Multicast delivery is one of the solutions to reduce the cost in a large video-on-demand (VoD) system. However, multicast transmission makes it more difficult to implement interactive functions for an individual user. In this paper, we first try to explore and evaluate the performance of different multicast VoD systems. A new scheme called single-rate multicast double-rate unicast (SRMDRU) is then developed to minimize the system resources for supporting full VCR functionality in a multicast VoD system. The proposed SRMDRU multicast system tries to double the transmission rate in unicast streams and then merge customers into multicast channels so that it can reduce the number of unicast streams. Computer simulations show that the multicast system using the SRMDRU scheme performs much better than other multicast systems in terms of system blocking probabilities. In addition, this scheme allows a multicast system to support true VoD services so customers can be served as soon as the system receives the requests.
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