DESIGNING A MULTIUSER HDTV STORAGE SERVER

Future advances in networking coupled with the rapid advances in stora ge technologies will make it feasible to build a HDTV-on-demand server (that provides services similar to those of a neighborhood videotape rental store) on a metropolitan area network. In this paper, we presen t a quantitative study of designing a multiuser HDTV server, and prese nt efficient techniques for storing multiple HDTV videos on disk and s ervicing multiple subscriber requests simultaneously, both under the c onstraint of guaranteeing HDTV playback rates. We develop a model that relates disk and device characteristics to the HDTV playback rate, an d derive a storage pattern for HDTV video streams that guarantees thei r real-time retrieval. Given multiple HDTV streams, we develop mechani sms for merging their individual storage patterns together. We propose an off-line merging algorithm that can be applied a priori and an on- line algorithm suitable for merging a new HDTV stream into a set of al ready stored HDTV streams, both of which yield a large improvement in space utilization over storing each or the streams independently. We s tudy various policies such as round robin and quality proportional for servicing multiple subscribers simultaneously. The quality proportion al algorithm retrieves video frames at a rate proportional (on average ) to the HDTV playback rates of subscribers, but uses a staggered togg ling technique in which successive numbers of retrieved frames are fin e tuned individually to achieve the servicing of an optimal number of subscribers simultaneously. The algorithm is powerful enough to accomm odate bounded availability of HDTV display buffers, and permits dynami c additions and deletions of subscriber requests in a transparent mann er (i.e., without causing discontinuity in the retrieval of any of the existing subscribers). In summary, our studies provide a quantitative demonstration of the technological feasibility and economic viability of HDTV-on-demand servers on metropolitan area networks.