ACD Atlas Computing Division Distributed Computing Systems

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DCS Projects: University of Lancaster



Sept 81 - Sept 84

The purpose of this research is to investigate the relative performances of Ring and Ethernet-like systems over a wide range of different operating conditions using a local computer network which can be implemented by means of either a Cambridge Ring or Strathnet (an Ethernet-like system).

The project started in September 1981 and the research assistant was appointed in October 1981. The Cambridge Ring was installed in February 1982. The major part of the work since then has been to produce a working system which would provide a suitable vehicle for the performance investigations. This has involved the construction of a file server based on an LSI-11/23 with a Winchester disc, the design of interprocess communication primitives between the various computers attached to the network, the design and implementation of a traffic monitor to enable meaningful statistics to be gathered from the network, and the implementation of the basic block drivers for the Polynet DMA Interface to the PDP-11s. In addition the Strathnet Access units are being modified to interface to the second port on the Polynet DMA Interface to allow the operation of a dual system (Ring or Ethernet-like). It is hoped that the dual system should be operational early in 1983.

As a part of the programme a DEC LSI-11/23 and a 10 MByte Winchester disc were purchased and four LSI-11/02 systems were given by DEC. Two of the four LSI-11/02 systems are being attached to the Cambridge Ring and the others to Strathnet. They will allow the investigators to look at the performance of personal machines attached to the two systems.

Over the past two years a number of papers have been given related to the work in progress and these are listed at the end of the report.

The past year has been mainly spent in setting up a dual system, both hardware and software, on which meaningful comparison measurements can be carried out. The first of these will be comparing the performance of our remote procedure call implementation across the Ring and Ethernet-like system respectively. Some preliminary work has been done in this area [8]. Digital Equipment Corporation (DEC) have shown interest in out work and are supporting a CASE student from October to look at the performance of their DEC Ethernet. This will enable us to compare the Ring against a commercially available Ethernet. In October the research group moved to the University of Lancaster.


1. G. S. Blair, D. Hutchison and W. D. Shepherd, MIMAS - a Network Operating System for Strathnet, 3rd International Conference on Distributed Systems, Florida, October 1982.

2. G. S. Blair, J. A. Mariani and W. D. Shepherd, A Practical Extension to UNIX for Interprocess Communication, Software Practice and Experience, 13,45-48 (1983).

3. W. D. Shepherd, G. S. Blair and D. Hutchison, Comparison of an Ethernet-like Communication System with the Cambridge Ring, Proceedings lEE, Vol. 129, Part E, No.4, July 1982.

4. D. Hutchison and W. D. Shepherd, An LSI-l1 Based Fileserver, DECUS UK Conference. University of Keele, March 1982.

5. D. Hutchison and P. Corcoran, A Microprocessor-based Local Network Access Unit, Microprocessors and Microsystems, Vol. 6, No. 1, Jan/Feb 1982.

6. G. S. Blair and W. D. Shepherd, A Performance Comparison of Ethernet and the Cambridge Digital Communication Ring, Computer Networks, Vol. 6, 1982.

7. D. Hutchison and W. D. Shepherd, Strathnet - A Local Area Network, Software and Microsystems, Vol. 1, No.1, October 1981.

8. G. S. Blair, D. Hutchison and W. D. Shepherd, Implementation of a Local Network Operating System, Localnet'83, London, March 1983, Online Publications, pp 387-398.

9. S. J. Muir, D. Hutchison and W. D. Shepherd, ARCA - A Network Fileserver, Computer Journal, Vol 28, No 3, p. 243 - 249

10. J. R. Nicol, G. S. Blair and W. D. Shepherd, CRS - A Powerful Primitive for Resource Sharing in UNIX, submitted to Software Practice and Experience.