Abstruct-Recent advances in networking, storage, and computer technologies are stimulating the development of multimedia on-demand services providing services similar to those of a neighborhood videotape rental store over metropolitan area networks. In this paper, we develop intermedia synchronization techniques for multimedia on-demand retrieval over integrated networks in the absence of global clocks. In these techniques, multimedia servers use lightweight messages calledfeedback units transmitted by media display sites (such as audiophones and videophones, generically referred to as mediaphones) to detect asynchronies among those sites. We present strategies by which the multimedia server can adaptively control the feedback transmission rate from that mediaphone, so as to minimize the associated overheads without permitting the asynchrony to exceed tolerable l i m i t s . We compare the performance of various resynchronization policies such as conservative, aggressive, and probabilistic. Performance evaluation of the feedback techniques indicates that their overheads are negligible; for a typical audidvideo playback environment, the feedback frequency was about one in hundred. The media-specific synchronization techniques described in this paper possess an important advantage as compared to those based on clock synchronization: skipping and pausing of media units at the time of resynchronization can be based on the semantic content of the media units, thereby minimizing perceptible degradations in quality of media playback.
In this paper, we define and formulate various policies for load management in distributed video servers. We propose a predictive placement policy that determines the degree of replication necessary for popular videos using a cost-based optimization procedure based on a priori predictions of expected subscriber requests. For scheduling requests, we propose an adaptive scheduling policy that compares the relative utilization of resources in a video server to determine an assignment of requests to replicas. To optimize storage utilization, we also devise methods for dereplication of videos based on changes in their popularities and in server usage patterns. Performance evaluations indicate that a load management procedure which uses a judicious combination of the diflerent policies performs best for most server configurations.Advances in storage technologies are making highperformance video servers a reality. These video servers are being deployed over emerging broadband networks to deliver a variety of interactive, digital video services to thousands of residential subscribers. To meet the scalability requirements in such large deployments, distributed video server architectures are being considered [3]. In this paper, we propose various methods for load management that are targeted at improving the cost-effectiveness of distributed video servers. The paper is organized as follows: Section 1 motivates the need for load management and discusses its implications on a video server's cost-performance.Section 2 presents the different policies for load management while Section 3 discusses more optimizations for load management. Section 4 presents a comparative analysis of the different policies. We conclude in Section 5 and outline areas for future research.
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