The Desk Area Network

Mark Hayter and Derek McAuley
University of Cambridge Computer Laboratory

May 1991

To appear in ACM Operating Systems Review

Abstract

A novel architecture for use within an end computing system is described. This attempts to extend the concepts used in modern high speed networks into computer system design. A multimedia workstation is being built based on this concept to evaluate the approach.

1 Introduction

High speed networks (100Mbit/s per access point) are currently being designed and coming into use as local area networks (LANs). The desire to support traffic with real time requirements (e.g. multimedia traffic) has lead many groups to propose the use of Asynchronous Transfer Mode (ATM1) for such networks. In the longer term the adoption of ATM by Broadband ISDN (B-ISDN) will give wide area ATM coverage. The effective use of these networks depends on the design of end systems which can utilise the bandwidth provided. The real producer or consumer of the data will be a particular processor or device within the end system, so besides considering the design of a network interface, consideration must be given to the method used to transfer the data between this interface and the real end points of communication.

LANs are normally thought of as connecting a set of autonomous machines, where there is a significant delay, compared to processor execution time, in data transfer. LANs also use a set of communication protocols to deal with the unreliability of data transfer between nodes and the consequences of node failure. On the other hand, interconnection networks have been used to link processors and memory systems in high performance multiprocessor machines, using simple protocols, typically transferring small data units (frequently single words or cache lines). In such a system, the communication is comparatively reliable leading to simpler control mechanisms, with failures usually treated as terminal.

We propose an architecture for the internal interconnection of a computer system, which combines various aspects of ATM LANs and traditional interconnection networks. An ATM switch is used to provide interconnections between the components

1We use ATM in the general sense defined in CCITT I.113 [2], `A transfer mode in which information is organized in to cells; : : : ', rather then to refer to specific properties of the ATM Layer in B-ISDN