We believe that the 'killer application' of active networking will be the provision of services which are not known to either the hardware manufacturer or the vendor at the time of network deployment. This would enable the rapid deployment of new services by third parties, and an unprecedented level of customisation by network administrators and end users. This vision, however, requires a degree of flexibility not yet seen in any of the currently proposed active router architectures. The lack of flexibility found in current active router designs has inspired us to develop a novel component-based active router architecture enabling extensible network programmability based on a progressive service composition framework. This document presents this architecture, LARA++, discusses its rudimentary concepts, and illustrates by example how its component architecture can benefit network programmability.

This document introduces a novel access control architecture for publicly accessible wireless overlay networks. The architecture is designed to address the problems of ubiquitous Internet service provisioning within the city of Lancaster. The proposed access control mechanism is based on the concepts of secure user authentication, packet marking, and network-level packet filtering. The novelty of the architecture lies in its use of microcellular layer three networks to acquire fine grained access control in a link independent manner. The paper describes the concepts behind the access control architecture and demonstrates to what extent it addresses the security, performance and extensibility concerns of public access packet switched wireless networks.

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.

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.>

Abstract The increasing use of multimedia 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.

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.>

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.

Distributed systems can be built to a client-server model in which one of the important servers is the file server, consisting of at least one processor and disk drive, attached to the network with the sole purpose of storing information on behalf of its clients. In the Department of Computing at Lancaster University we have designed and built a file server which is connected to both of our networks: an Ethernet-type network (called Strathnet, of local design) and a Cambridge Ring type network. The Arca File Server is based on work started at Cambridge University. This paper describes the background of file servers for local networks and the design and implementation of our system.

This paper describes the hardware and software architecture of a gateway between an Ethernet-style local area network called Strathnet and an X.25 packet switched network (British Telecom's PSS). The hardware is based on a Motorola 68000 processor using the VME bus, and peripheral boards based on an 8-bit 68120/1 processor for the local network and the X.25 interfaces. The software is layered from the low-level executive, through the three X.25 levels and the transport layer, and through the corresponding layers on the local network side, to the bridging software itself. Both hardware and software are designed so that the system can be a general-purpose gateway: for example, the local area network peripheral board could be replaced by a ring type interface, and the software within the local network layers could similarly be replaced.

Abstract This paper describes the steps involved in writing a server for the Cambridge Model Distributed System (CMDS). The first part of the paper describes the essential components of the system and is followed by a description of the Ancilla server. Finally a number of conclusions are drawn.