ACD Atlas Computing Division Distributed Computing Systems

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DCS Projects: Polytechnic of Central London



April 83 - March 85

MININET is a local area network aimed at real-time scientific and process control applications. The network employs packet switching technology to achieve highly reliable interconnection of a heterogeneous assortment of instrumentation devices as well as mini and microcomputer hosts.

This network utilises short fixed-length packets (Le. a word switching approach) to achieve ultra-high transparency to user devices which generally are not network conscious. Its high-speed word handling capacity provides the short trans-network response times for data or control bursts essential for meeting the real-time deadlines of on-line instrumentation. MININET has a flexible modular structure of arbitrary topology. composed of two main components (nodes which are either Stations or Exchanges) which can be arranged in nearly any convenient layout. A multiplicity of different links can be supported, with one MININET cheerfully accommodating slow-speed links (like modems) and also high-speed links (such as fibre optics).

In OSI Reference Model terms, MININET is a true network since communicating nodes do not have to be connected to a common data link, but may transfer information via one or more intermediate nodes. MININET is unique in the degree of Network Layer (Level 3) services which are being built in as inherent features. Users can construct their own end-to-end communication upon MININET without the need for host computers. Operational bottlenecks, such as low transaction speeds, that plague most other Level 2 local area networks are avoided by provision of very high-speed special-purpose processors (the nodes) developed for MININET. The latest version of the Station (now under test) meets its specification of one megapacket per second internal processing speeds!

Packets 32 bits in length are interchanged between devices, transducers or computers attached to up to 64 nodes spread over an area typically of 2 km expanse. Each Station can accommodate up to 64 user devices (attached via the IEEE 488 interface or an intermediate interface known as DIM), so a sizeable user community can be served with easily-reconfigured virtual connections.

MININET is being jointly developed by the Signal Processing Group at the Polytechnic of Central London (PCL) and the Automatics Institute at Bologna University. Support has come from a succession of grants awarded by SERC, the Italian CNR, NATO and EEC. Plans for the coming year call for an increasing effort to be directed to pre-product development activities in consultation with industry, in parallel with the on-going research aspects.

Earlier demonstrations have centred on the computer room type of resource sharing environment that has been continually served by a low-speed prototype Station at Bologna University since February 1980. There, several small computers have been flexibly connected into a pool of slow peripherals such as line printers and paper tape readers. Incorporation of the first full-performance Station during 1983 into an environment at PCL emphasising support of real-time speech data collection with remote digital signal processing is expected to provide useful stress testing experience for MININET's demanding high-speed instrumentation role.

Future research activities are being concentrated on efficient incorporation of popular Level 2 multipoint data communication media, such as rings and buses, as special cases of MININET channels. Utilisation of multiple Cambridge Rings appears to be a particularly fruitful possibility. Near-term objectives include development of an interface to a Cambridge Ring and an IEEE 488 network port.



April 79 - March 81


Microprocessors and microcomputers are being coupled together in increasingly large numbers, reaching several hundred or more, in a tightly or loosely coupled manner as distributed computing structures which include complex interconnection mechanisms and interfaces to link these to an application. Superimposed on this hardware structure, software is written to provide the communication protocols, synchronisation between sequential processes, application programs and so on. Considering the complexity of such systems, however, currently there are no adequate methods to understand and evaluate many of the basic architectural and software options that exist when a distributed computer system is designed to satisfy the requirements of a particular application environment.


A software design package called MICROSS has been written which is capable of giving a designer the ability, by means of an interactive terminal, to model his system using standard, or user defined building blocks and their interconnections. Once a model is defined, then a number of simulation runs can be performed to derive principal performance figures such as delay times and throughput. MICROSS is currently on a DEC 10 computer accessed by means of a Tektronix 4014 terminal.


1. Y. Paker, H. English and M. Bozyigit, NPL Multicomputer Ring Modelling and Simulation, in IFIP we 6.4 Workshop on Ring Technology, Canterbury, September, 1983, ed. I.N.Dallas and B.Spratt, North-Holland Publishing Company, 1983.

2. M. Bozygit, H. English and Y. Paker, MICROSS: Graphics Aided Simulation of Distributed Computer Systems, in Synchronization, Control and Communication in Distributed Computer Systems, ed. Y.Paker and J.P.Verjus, Academic Press, 1983.

3. Y. Paker and M. Bozygit, Computer-Aided Multi-Microporcessor System Modelling, Simulation and Performance Evaluation, Project Report 1, PCL September 1979.

4. M. Bozygit and Y. Paker, Computer-Aided Multi-Microprocessor System Modelling, Simulation and Performance Evaluation - MICROSS, Project Report 2, PCL December 1979.

5. M. Bozygit, A Dense Variable Topology Multi-Computer System: Specification and Performance Analysis, PhD Thesis, PCL May 1979.