Performance Evaluation of the Deadline Credit Scheduling Algorithm for Soft-Real-Time Applications in Distributed Video-on-Demand Systems

摘要

Video-on-Demand (VoD) systems are expected to support a variety of multimedia services to the users, such as tele-education, teleconference, remote working, videotelephony, high-definition TV, etc. These applications necessitate abundant bandwidth and buffer space as well as appropriate software and hardware for the efficient manipulation of the network's resources. In this work we investigate a promising scheduling algorithm referred to as the Deadline Credit (DC) algorithm, which exploits the available bandwidth and buffer space to serve a diverse class of prerecorded video applications. We provide simulation results when the DC algorithm is applied to a hierarchical architecture distributed VoD network, which fits the existing tree topology used in today's cable TV systems. The issues investigated via the simulations are: the system utilization, the influence of the buffer space on the delivered Quality of Service, and the fairness of the scheduling mechanism. We examine cases with homogenous as well as diverse video streams, and extend our system to support interactive VCR-like functions. We also contribute a modification to the DC algorithm so that in cases when the video applications have different displaying periods, the video streams obtain a fair share of the network's resources. Finally, we validate our results by simulating actual videos encoded in MPEG-4 and H.263 formats.