Improvements in fibre optic communication and in VLSI for network switching components have led to the consideration of building digital switched networks capable of providing point to point communication in the gigabit per second range. Provision of bandwidths of this magnitude allows the consideration of a whole new range of telecommunications services, integrating video, voice, image and text. These multi-service networks have a range of requirements not met by traditional network architectures designed for digital telephony or computer applications. This dissertation describes the design, and an implementation, of the Multi-Service Network architecture and protocol family, which is aimed at supporting these services. Asynchronous transfer mode networks provide the basic support required for these integrated services, and the Multi-Service Network architecture is designed primarily for these types of networks. The aim of the Multi-Service protocol family is to provide a complete arc...

We study the problem of transmitting time constrained synchronous messages in a slotted ring based local area network, carrying synchronous and asynchronous traffic. A bandwidth allocation scheme for synchronous messages is developed on top of a media access control protocol that assigns preemptive priority to synchronous traffic over asynchronous traffic. We derive sufficient conditions for schedulability of time critical synchronous messages and show that the scheme achieves high levels of schedulable utilization. A slot access protocol is proposed for synchronous streams that implements the allocation scheme with minimal additional overhead and loss of schedulable utilization. The protocol is distributed in the sense that any node can locally determine if it can use a slot, without exchanging any explicit messages with other nodes. 1 Introduction Many safety-critical real-time applications like process control, air-traffic control, factory automation etc., must operate under string...

Handling audio and video in a digital environment requires timely delivery of data. This paper describes the principles adopted in the design of the Pandora networked multi-media system. They attempt to give the user the best possible service while dealing with error and overload conditions. Pandora uses a sub-system to handle the multi-media peripherals. It uses transputers and associated Occam code to implement the time critical functions. Stream implementation is based on self-contained segments of data containing information for delivery, synchronisation and error recovery. Decoupling buffers are used to allow concurrent operation of multiple processing elements. Clawback buffers are used to resynchronise streams at their destinations with minimum latency. The system has proved robust in normal use, under overload, and in the presence of errors. It has been in use for a number of years. The principles involved in this design are now being used in the development of two complementar...

a continuous media file server is presented to demonstrate the effectiveness of design decisions and to illuminate the impact of continuous media storage on computer architecture. To my family Preface I am grateful to my supervisor Professor Roger Needham for the opportunity and encouragement to pursue this research. My thanks and appreciation also go to numerous members of the Computer Laboratory. Particular members of the System Research Group deserve special mention including, Joe Dixon, Cosmos Nicolaou, Derek McAuley, Glenford Mapp, Cormac Sreenan, Eoin Hayden, Tim Wilson, Richard Black and Mark Hayter. Their valuable advice and constant stimulation provided an excellent environment in which to develop my understanding. For reading and commenting on earlier drafts of this dissertation, I thank Cormac Sreenan, Richard Black, Simon Crosby, Cosmos Nicolaou, Roger Needham, Tim Wilson, Heather Leitch, Mark Hayter and Derek McAuley. My deepest appreciation i

Ring network architectures that employ spatial reuse permit concurrent transmissions of messages over different links. While spatial reuse increases network throughput, it may also cause starvation of nodes. To alleviate this problem, various policies have been suggested in the literature. In this paper we concentrate on a class of such policies that achieve fairness by allocating transmission quotas to nodes. For such policies, weprovide mechanisms for improving delays and increasing overall throughput without compromising fairness.

The development of broadband ATM networking makes it attractive to use computer communication networks for the transport of digital audio and motion video. Coupled with advances in workstation technology, this creates the opportunity to integrate these continuous information media within a distributed computing system. Continuous media have an inherent temporal dimension, resulting in a set of synchronisation requirements which have real-time constraints. This dissertation identifies the role and position of synchronisation, in terms of the support which is necessary in an integrated distributed system. The requirements for synchronisation are divided into two categories. Stream synchronisation is concerned with issues such as delay jitter with respect to the presentation of a single continuous media stream, as well as maintaining the relationships which may exist between multiple streams. Event synchronisation allows applications and system services to co-ordinate their behaviour bas...

This paper describes the implementation of an ATM protocol stack as a protocol family within a 4.3 BSD derived Unix. A novel approach to the implementation of the management and control functions for the ATM protocol stack has been adopted. The data path is implemented within the kernel but all control and management functions are implemented by a user space daemon. An encapsulation of IP on the ATM protocol is provided by means of a logical IP interface. The mapping of IP addresses to ATM addresses is performed by the user space daemon.

Distributed systems have traditionally tackled the problems associated with the inter-connection of a number of computer systems. Until recently the focus of this research has been on the development of solutions to the technological problems involved. The emergence of Computer Supported Cooperative Working (CSCW) has challenged this technological perspective by focusing on the group-working of a number of users. This paper briefly introduces the state of the art in CSCW and relates the general characteristics of existing CSCW systems to a variety of trends in distributed computing. It is argued a reasonable correspondence exists between CSCW and distributed systems in terms of their geographical nature and style of interaction. However, a disparity appears when we examine how cooperation is represented and controlled in both CSCW and distributed systems. Strict distribution transparency is highlighted as the most significant manifestation of this disparity, often discouraging users fr...

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This paper advocates local area networks using the Asynchronous Transfer Mode where data is carried in the payloads of fixed size cells. We describe the design and performance of a simple ATM host interface for inexpensive computers together with the MSNA protocol architecture. A feature of the MSNA architecture is that it can provide ATM virtual circuits directly to applications by demultiplexing to a degree normally associated with the transport layer of a protocol stack. This leads to further simplification and efficiency in end-system implementation. We discuss implementations of the ATM adaptation layer of varying complexity, suitable for end-systems ranging from imbedded micro-controllers to Unix' file servers, and discuss the appropriate place for the adaptation layer to be terminated in a multi-media workstation.