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Video on demand (VOD) is expected to be the first of many Video Dial Tone (VDT) services that will bring broadband connections to residential customers. Significant research is being undertaken to identify cost effective broadband access technologies. However, much less effort has been expended on video servers and backbone architectures. In this publication we highlight what we believe are the issues relevant to obtaining a critical understanding of the VDT architecture. These issues are shared between the video server and its storage elements, and the placement of key architectural elements (transport, storage and switching) within the network. In particular, it will be argued that establishing a balance between centralized and distributed storage of movies plays a key role in optimizing the backbone network. It also places new requirements on server architecture. Intuitively, storing copies of popular movies close to the users (e.g. in the central office) reduces demand on the network, while hauling movies from a central storage location (e.g. the VIP site) potentially increases utilization of storage resources and hence the number of movies in the system and the resulting cost of storage.
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