Doug Shepherd

The Design of a Storage Server for Continuous Media

The increasing use of multimeda in computing is demanding more powerful computer hardware and system software. In particular, the stringent demands placed on multimedia file servers are unable to be satisfied by current magnetic disk technology or by current file systems techniques. This paper describes the design and implementation of a file server which has been specially optimized for continuous media. The critical performance issues which this paper addresses are the use of disk striping to provide high bandwidth, optimized disk layouts, hard real-time disk scheduling to ensure stream storage and retrieval guarantees are met, and a user interface to support high level multimedia abstractions

Filters: QoS support mechanisms for multipeer communications

The nature of distributed multimedia applications is such that they require multipeer communication support mechanisms. The multimedia traffic needs to be delivered to end-systems, networks, and end-users in a form that they can handle while satisfying the constraints imposed by the multimedia application. Quality-of-service (QoS) mechanisms that can ensure full quality media playout at high-performance workstations, while at the same time providing appropriately filtered lower quality media for playout at other end-systems, are required. Existing multicast support mechanisms are deficient for this purpose, in a heterogeneous environment, because they work on a common denominator premise where the quality delivered depends on the least capable link or node involved in the multicast session. This paper begins by discussing video compression; it proposes and analyzes the use of filtering mechanisms as means of supporting disparate receiver capabilities and QoS requirements. The paper describes the implementation of a number of filtering mechanisms and highlights the communications architecture within which these mechanisms are built. This architecture constitutes a specific network topology and a new protocol family developed within a UNIX-like operating system.

Extending OSI to support synchronization required by multimedia applications

Abstract OSI is rapidly gaining acceptance as the international standard for the internetworking of different computer systems. However, since its conception over a decade ago there have been significant advances in network technologies resulting in higher speeds and greater reliability. With the emergence of new network standards such as B-ISDN, speeds of up to 140 Mbit/s are now realizable. One of the challenges that OSI must meet is to show that it can be extended or adapted to support the wide range of traffic that will be run across these new networks and in particular to support multimedia applications. This paper discusses the problems that must be solved to support multimedia and proposes how OSI could be extended to handle the synchronization requirements of multimedia applications.

The design of a QoS-controlled ATM-based communications system in Chorus

We describe the design of an application platform able to run distributed real-time and multimedia applications alongside conventional UNIX programs. The platform is embedded in a microkernel/PC environment and supported by an ATM-based, QoS-driven communications stack. In particular, we focus on resource-management aspects of the design and deal with CPU scheduling, network resource-management and memory-management issues. An architecture is presented that guarantees QoS levels of both communications and processing with varying degrees of commitment as specified by user-level QoS parameters. The architecture uses admission tests to determine whether or not new activities can be accepted and includes modules to translate user-level QoS parameters into representations usable by the scheduling, network, and memory-management subsystems. >

Protocol support for distributed multimedia applications

In this paper we describe ongoing work in protocol support for distributed multimedia applications. This work concerns the provision of suitable transport mechanisms to convey multimedia information (text, and digital voice and video) between multimedia workstations in a distributed system. There are two parts to the Lancaster multimedia work. First, we have developed an abstract model for multimedia communications that is based on the use of streams; and second, we have built an experimental system on which to test the implementation of protocols based on this model. This paper reports on both aspects of the Lancaster work, describing the results so far and identifying areas to be investigated further.

The Design and Implementation of a Continuous Media Storage Server

This paper describes the design and implementation of a file server specially optimised for the storage and retrieval of continuous media. The issues which this paper addresses are disk striping, optimised disk layouts, real-time algorithms, and disk head scheduling.

Extending the Chorus Micro-Kernel to Support Continuous Media Applications

Currently, popular operating systems are unable to support the end-to-end real-time requirements of distributed continuous media. Furthermore, the integration of continuous media communications software into such systems poses significant challenges. This paper describes a design for distributed multimedia support in the Chorus micro-kernel operating system environment which provides the necessary soft real-time support while simultaneously running conventional applications. Our approach is to extend existing Chorus abstractions to include QoS configurability, connection oriented communications and real-time threads. The design uses the following key concepts: the notion of a flow to represent QoS controlled communication between two application threads, a close integration of communications and thread scheduling and the use of a split level scheduling architecture with kernel and user level threads. The paper shows how our design qualitatively improves performance over existing micro-kernel facilities by reducing the number of protection domain crossings and context switches incurred.

A network interface unit to support continuous media

The combination of high-speed multiservice networks and multimedia workstations offers considerable potential for the development of distributed multimedia applications. A key problem is how to integrate continuous-media types such as audio and video into a distributed workstation environment. An experimental system architecture based on a specialized multimedia network interface that attempts to provide this integration is described. The design and implementation of this system are discussed in depth in terms of workstation enhancement and distributed system support. A new approach to the problem of media synchronization is introduced, and the importance of quality of service in the architecture is highlighted. Experiences encountered during this work are described, comparison with other approaches is made, and likely future developments in multimedia network interfacing are discussed. >

LARA: A Prototype System for Supporting High Performance Active Networking

There are a number of alternative directions in which active networking is progressing, each of which have their own advantages and disadvantages. This paper presents the Lancaster Active Router Architecture (LARA), as a means to integrate these distinct active network environments in a single system, to allow increased flexibility in network programming. There are a number of issues involved in accomplishing this, including scalability, resource management, performance and security. The remainder of this paper describes our prototype composite hardware/software solution, which takes the first steps towards tackling these issues.

A knowledge-based operating system

The recent developments in ‘fifth generation’ computing, for example in the areas of programming environments and man-machine interfaces, have shown up inadequacies in the current generation of operating systems. In addition, most operating systems are designed to run on a single computer (uniprocessor or multiprocessor) and to provide a multi-programming environment. Consequently, they cannot realise the full potential offered by a new class of computer systems consisting of computers interconnected by a high-speed local area network. In this paper we present a proposal for an operating system kernel to meet these new demands. We concentrate on one particular aspect of the design – its knowledge base. It is suggested that a knowledge base can provide support for more intelligent systems. It is further suggested that this knowledge base should be at the heart of the operating system design. Some examples are presented to illustrate the use of a knowledge base to support more intelligent applications and to provide a better environment for the user.