Cost-optimal Dimensioning of a Large Scale Video on Demand System

We introduce a video distribution architecture where the prefix of the video is delivered on demand by a prefix server while the body of the video is broken in equal length segments and each segment is periodically transmitted by a central server. The combination of open-loop distribution for the video body and closed-loop multicast transmission for the video prefix makes the overall system highly scalable and very cost-efficient. Given that video distribution architecture, we develop a detailed analytical model for the cost of delivering a video as a function of the popularity of that video. In difference to previous studies, our model includes the cost for server storage and server I/O and represents the video distribution network as an m-ary multicast tree, which allows us to precisely capture the cost for multicast transmission. Our analytical model allows to compute the cost-optimal prefix length as well as the optimal location of prefix servers in the video distribution system. Our results show how the length of the prefix and the placement of the prefix servers depend on the video request rate. In particular, placing the prefix servers close to the clients, as was suggested in previous studies, is often not cost-optimal.