On the efficient retrieval of VBR video in a multimedia server

In this paper, we consider the retrieval of variable bit rate (VBR) video data from the 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, namely, first to determine which data to access by what deadline and second, 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.