A quasi-static retrieval scheme for interactive VOD servers

Video-on-demand (VOD) servers need to be eeciently designed in order to support a large number of users viewing the same or diierent videos at diierent rates. In this paper , we propose a simple quasi-static retrieval scheme that may be used for this purpose when interactive disk-array based video servers are used. We assume presence of no buuer at the server and hence, all retrieved segments are immediately transmitted to the appropriate users. Such a retrieval scheme employs a macro-slot assigner and a disk scheduler. Macro-slots deene 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 scheduler uses the Non-preemptive Earliest Deadline First (N-EDF) algorithm to determine a valid schedule for segment retrieval. In order to increase the number of users that can be served by the system, the number of disk seeks in a service round needs to be decreased. This is done in the Scan-N-EDF algorithm by appropriately grouping retrievals and using the scan algorithm within each group. For a given video segment size, the amount of buuer required at each user's set-top box is reduced to two video segments. Guarantees are provided for the avoidance of video starvation as well as buuer overrow at each user's set-top box.