A QUASI-STATIC RETRIEVAL SCHEME FOR INTERACTIVE VOD SERVERS

Video-on-demand (VOD) servers need to be efficiently designed in order to support a large number of users viewing the same or different vide os at different rates. In this paper, we propose a simple quasi-static retrieval scheme that may be used for this purpose when interactive d isk-array based video servers are used. We assume presence of no buffe r at the server and hence, all retrieved segments are immediately tran smitted to the appropriate users. Such a retrieval scheme employs a ma cro-slot assigner and a disk scheduler. Macro-slots define a duration of time in a service round within which one video segment needs to be retrieved for a user. Having assigned macro-slots to users, the disk s cheduler uses the non-preemptive earliest deadline first (N-EDF) algor ithm to determine a valid schedule for segment retrieval. In order to increase the number of users that can be served by the system, the num ber of disk seeks in a service round needs to be decreased. This is do ne in the Scan-N-EDF algorithm by appropriately grouping retrievals an d using the scan algorithm within each group. For a given video segmen t size, the amount of buffer required at each user's set-top box is re duced to two video segments. Guarantees are provided for the avoidance of video starvation as well as buffer overflow at each user's set-top box. (C) 1997 Elsevier Science B.V.