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Large scale video-on-demand systems require that the servers offering the video retrieval and playback services are arranged as a distributed system in order to support a large number of concurrent streams. If such a system is hierarchical, an end-node server handles the requests from a particular area, the next server in the hierarchy takes the request over for several end-node servers if those can not answer the request and so on. This architecture provides for cost efficiency, reliability and scalability of servers. The end-node servers store only a limited set of the overall available information which changes over time due to user interests. If a video is requested which is not available, this server contacts the next server in the hierarchy.
Griwodz et al. (Wed,) studied this question.