Video-on-demand (VOD) servers need to be efficiently designed in order to support a large number of users viewing the same or different videos at different rates. While considering a disk-array based VOD server, use of a shared buffer at the server end may be more economical than the sole use of dedicated buffers at each user's end. In this paper we propose a simple buffer sharing architecture that may be used when disk-array based video servers are used. Our aim is to support the maximum number of users for a given number of video server disks while employing a simple scheme requiring less buffer space. The number of video segment retrievals that can occur within a certain time (the service round) is maximum when the scan disk scheduling algorithm is used. Consequently, we shall assume use of the scan algorithm for disk retrieval. The VOD server has a buffer manager that directs retrieved segments to appropriate buffer locations depending on their release and deadlines. The release and deadlines of segments are such that buffer requirement at the user's set-top box is minimized to two video segments while avoiding video starvation and buffer overflow at the user's end. We propose a novel scheme for the operation of the shared buffer that aims at increasing buffer utilization and decreasing cell loss due to buffer overflow. An ATM based broadband network is assumed and all segments are stored in buffers as fixed length ATM cells.
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