Constant Data Length Retrieval for Video Servers with Variable Bit Rate Streams

Video servers store digitized, compressed continuous media information on high-capacity secondary or tertiary storage [6]. The secondary storage devices allow random accessible and provide short seek times compared to tertiary storage. Video server design differs significantly from that of traditional data storage servers due to the large size of the objects stored and the real-time requirements for their retrieval. The critical resources in a video server are disk bandwidth, storage volume, and main memory. Given a fixed amount of these resources, a video server can only deliver a limited number of video streams simultaneously. Before admitting a new client, a video server must use an admission control algorithm to check if there are enough resources for serving the additional client. We identify and formalize schemes for the retrieval of variable bit rate video data from magnetic disks. Traditional methods, such as the cyclic retrieval of variable size data segments or the retrieval at the stream’s mean bit rate, either cannot profit from smoothing media traffic over larger intervals, or suffer from excessive buffer demand and latency. We derive a novel technique that covers existing methods as special cases. While offering a deterministic service, the novel scheme can drastically decrease the buffer requirement and server latency in an interactive multimedia service. 2. Deterministic Retrieval Schemes in Video Servers