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

Abstract

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, highdefinition 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.Keywords: Scheduling video applications, distributed VoD systems, MPEG-4, H.263, VCR-like operations. IntroductionTelecommunication networks have lately extended to support a variety of services to the users such as tele-education, teleconference, remote working, videotelephony, high-definition TV, web video streaming, etc. These applications dictate the need for high-speed networks, and also necessitate the appropriate software and hardware for the efficient integration of a diverse class of applications with different characteristics. These demanding requirements led to the concept of broadband integrated digital networks (B-ISDN), which are systems of high capabilities that enable the transmission of several different applications.Several research areas have been developed in order to increase the efficiency of the network and keep the Quality of Services (QoS) at a satisfactory level. One significant area that affects the quality provided by the network is the scheduling process. Since several applications should be concurrently serviced, the role of the scheduling process is to select each time the application that should be served next.The applications that telecommunication networks support are generally classified into two categories based on the delay that they can undergo during connection: the real time and the nonreal time applications. Real time applications involve a kind of interactivity and consequently can tolerate no delay. The characteristic of these applications is that the network's resources which provide the services need to be reserved for the duration of the connection. This necessitates ample bandwi...