Scheduling Algorithms for Application-Level QoS Support of Continuous Media Streams

The Quality of Service (QoS) of real time applications is affected in a rather direct manner by the timely delivery of Application-level Data Units (ADUs) which are typically mapped into several Network-level Data Units (NDUs). As a consequence, it would be reasonable to associate a common deadline with all the NDUs in one ADU and develop a scheduling policy that aims to maximise the number of ADUs that are delivered by their respective deadlines. In the first part of the paper, an ADU-based Earliest Due First (EDF) scheduling policy is investigated under periodic ADU arrival processes which are typical of continuous media streams. The proposed policy can be implemented in terms of a simple First ADU In - First ADU Out (FAI-FAO) policy and it is shown to improve on the ADU dropping rate induced by FIFO policies of comparable complexity. In the second part of the paper, the more complex and effective Size-Deadline Sensitive(SDS) scheduling policy is proposed and investigated under gener..