Multimedia data have specific temporal presentation requirements. For example in video conferencing applications voice and images of participants must be delivered and presented synchronously. These requirements can be achieved by scheduling or managing system resources. We present a technique called limited a priori scheduling (LAP) to manage the delivery channel from source to destination for digital multimedia data. By using delay estimation a LAP scheduler can retrieve stored digital media spanning arbitrary networks with unspecified delays. The use of delay estimation also facilitates selective degradation of service in bandwidth and buffer limited situations. Such degradation enables the continuous real-time playout and synchronization of various media arriving from different sources. The performance of the LAP scheduler is described based on implementation and experimentation using Ethernet.
In this paper we describe the Virtual Video Browser (VVB) software application designed to allow the interactive browsing and content-based query of a video database and to facilitate the subsequent playout of selected titles. The VVB is a manifestation of our mechanisms for the location, identification, and delivery of digital audio and video in a distributed system which can be extended to several application domains including multimedia-based home entertainment, catalog shopping, and distance learning. The VVB employs a two phase retrieval process to serve its users. In the query phase, user queries are sent to a metadata server for processing. In the subsequent playout phase, a connection is established between the client workstation and a video server for the delivery of video data. The VVB incorporates a simple query interface that lets users specify their preferences to the system and retrieve the appropriate video. The application is designed to work in a distributed environment where video sequences are stored in different databases interconnected via a network. It has been shown to be a viable target application useful for investigating research problems related to building interactive multimedia systems.
Abstract-A coherent computer-based multimedia presentation requires the use of real-time scheduling theory applied to system resources including storage devices, the bus, and network. In this paper we present a scheduling technique which is essentially static in nature during periods of network quiescence, but becomes dynamic in response to detection of network load changes or user interaction.This mechanism, called the limited a priori (LAP) scheduler, is an extension of earlier work on scheduling which assumed guaranteed system loading characteristics. The LAP scheduler determines network load changes and estimates packet delay using a dynamic filtering algorithm. We show the bounds of accuracy for this technique and describe its suitability with respect to multimedia traffic across an FDDI network.
High-speed networks ard high-performance workstations are necessary but not sufficient to support distributed multimedia applications. A real-time scheduling system designed for multimedia data types is also required to orchestrate communications channels, disk storage units, output devices, and the CPU. These subsystems are coordinated to accommodate the special requirements of multimedia data: timely retrieval, transmission, and delivery with permissible levels of data loss and corruption.In this paper we present our framework for the use of real-time scheduling disciplines to support time-dependent multimedia data in a distributed-data environment. Within this framework we propose the application of a statistical resource reservation mechanism and a real-time session scheduler. Furthermore, we relate scheduling and quality of service in a summary of the objectives of multimedia service provision and negotiation.
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