Abstract-One approach to supporting continuous media traffic is via resource reservation at connection establishment time. The shortcomings of this approach are the lack of flexibility in re-negotiating bandwidth parameters after connection establishment and the inability to react to changing server load conditions. In this paper we propose a "selected access scheme" for re-negotiating continuous media delivery from a video-on-demand server. We consider the overall system perspective on resource availability rather than a per-connection resource management scheme. The selected access scheme is combined with data placement strategies for the server to dynamically access desired video frames from a shared storage device. This approach is especially suitable for video data compressed and stored using an inter-frame encoding scheme such as specified by the MPEG standard. Simulation results show that the proposed model can utilize server bandwidth, improve the reliability of playback, reduce the buffering needed, and support VCR-like functions without blocking user access to the storage device.

Concurrent retrieval of continuous media from a physical storage device can be achieved by interleaving data and providing a suitable scheduling algorithm. Scheduling approaches that exploit gains from statistical multiplexing are susceptible to a non-zero probability of frame loss due to the variable-bit-rate characteristic of compressed video. With interframe encoding schemes (such as specified by the MPEG standard), the losses propagate, resulting in a net loss of frames that exceeds the fraction of missing data. In this paper we describe a mechanism for the storage and retrieval of MPEG-encoded video from a single disk storage system. The scheme balances the need for the reliable delivery of MPEG frames with the desire to support the largest number of sessions. Our approach reorganizes the MPEG-encoded video stream based on the relative importance of the frames and maps them to the storage device geometry. The reorganization reduces the impact of frames lost due to missed deadlines and distributes the frame losses over time and among sessions. Simulation results show that the new approach improves performance when compared to conventional storage and scheduling schemes.