To achieve scalable and efficient on-demand media distribution, existing solutions mainly make use of multicast as underlying data delivery support. However, due to the intrinsic conflict between the synchronous multicast transmission and the asynchronous nature of on-demand media delivery, these solutions either suffer from large playback delay or require clients to be capable of receiving multiple streams simultaneously and buffering large amount of data. Moreover, the limited and slow deployment of IP multicast hinders their application on the Internet.
To address these problems, we propose asynchronous multicast, which is able to directly support on-demand data delivery. Asynchronous multicast is an application level solution. When it is deployed on a proxy network, stable and scalable media distribution can be achieved. In this paper, we focus on the problem of efficient media distribution. We first propose a temporal dependency model to formalize the temporal relations among asynchronous media requests. Based on this model, we propose the concept of Media Distribution Graph (MDG), which represents the dependencies among all asynchronous requests in the proxy network. Then we formulate the problem of efficient media distribution as finding Media Distribution Tree (MDT), which is the minimal spanning tree on MDG. Finally, we present our algorithm for MDT construction/maintenance. Through theoretical analysis and experimental study, we claim that our solution can meet the goals of scalability, efficiency and low access latency at the same time.