Patching is an attractive technique for building efficient video-on-demand systems. However, since Patching assumes the existence of IP Multicast, implementing Patching on the current Internet is a challenging task because the Internet is based on IP Unicast only. In this paper, we propose an overlay technique called Vcast for enabling multicast services on the application layer, as a way to support the implementation of Patching. Unlike earlier overlay multicast schemes, Vcast does not introduce any global topology for the overlay and therefore avoids control overhead to maintain it. Vcast can configure itself adaptively to the changing network traffic, and is tolerant to failures prone to happen frequently in dynamic environments such as the Internet. In addition, Vcast provides load balancing among network nodes by employing the Round-robin approach in selecting delivery paths for clients.
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