Video-on-demand (VoD) is a service that has received much attention recently and the concept has become popular with computer and communication companies. Basically, VoD consists of a video server, interconnection network and user display equipment (UDE). It provides a similar service to the neighbourhood rental store. Videos or movies are distributed from the video server to users upon request through the network and users can view interactively using their UDE along with VCR-like functions (e.g. forward, rewind, pause and resume). VoD offers a convenient service since users do not have to leave their homes, which also leads to shorter response times than with today's video stores. One important aspect of any VoD is the storage scheme used, which affects the amount and type of storage required, the maximum number of concurrent video streams and the average waiting time experienced by users of the service from the moment they choose a video to the moment video playback starts. The paper reviews some well-known storage schemes, such as the phase-based method and the phase-based-with-replication method, and then proposes two new schemes that further increase the number of concurrent streams and reduce the waiting time, while reducing the total storage space required. These new schemes rely on two concepts called immediate playback RAM and sustainable playback storage. Using a case study, the new schemes are briefly compared with an existing scheme and their strengths and shortcomings are highlighted. Using some typical values, analyses are carried out that quantify the performance gain resulting from the new storage schemes.
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