On the efficient retrieval of VBR video in a multimedia server

Abstract

Considers the retrieval of variable bit-rate (VBR) video data from a storage server subject to the constraint that the server's buffer between its disk and network subsystem neither empties nor overflows. Our approach is based on the realization that there are two separate decisions to be made: firstly, to determine which data to access by what deadline, and secondly, how to schedule the data access. These decisions are the responsibilities of the data access and data scheduling policies. In the context of data access policies, we examine both the constant time length (CTL) and constant data length (CDL) policies. We find that increasing either the round length (for CTL access) or the fixed data size (for CDL access) allows data retrieval to be "smoothed out" over time. We then examine round-based and deadline-based data scheduling in conjunction with CTL and CDL data access policies. We find that two deadline-based scheduling policies that we propose ("lazy EDF" and "workahead CTL-round") allow a significant additional amount of smoothing to be achieved over traditional round-based data scheduling.