A Client-Controlled Adaptation Framework for Multimedia Database Systems

Multimedia applications require continuous delivery of time-dependent data. In best-effort systems where no resource reservation is possible, adaptation strategies are necessary in case of high system load. We propose an adaptation framework for a client-pull architecture where continuous data are requested and buffered by the presenting client. The current client buffer utilization is used as an indicator for performance bottlenecks and determines which adaptation strategy the client invokes. The aim of the invoked adaptation is to reduce the data volume which has to be transferred to the client in a controlled manner leading to a graceful degradation of presentation quality. Frequent switches between different qualities are avoided by using a hysteresis and by specifying smooth transitions between different degrees of data dropping. As we consider adaptation control only at the client side we believe that our approach can easily be used for achieving intra-media synchronized presentations in most open and heterogeneous environments.