Project Universe Shows Feasibility of Linking LANs Through Satellites.
Project Universe is an experiment linking local-area networks (LANs) by satellite. Creation of the high-bandwidth network provided the opportunity to research a number of new computer-science techniques for the first time:
* Individual computers at separate sites have been made to work collectively and simultaneously on a single problem.
* Distant computers have been accessed remotely with the same performance quality experienced by local users.
* Slow-scan television pictures and illustrations have been transferred quickly and efficiently from one site to another.
* Voice communications has been carried throughout the network.
The Universe Project is made up of Cambridge rings and other types of LANs at six sites in the United Kingdom, linked via the European Space Agency's Orbital Test Satellite (OTS), which is in geostationary orbit 22,370 miles above the equator. Earth stations consist of a three-meter-diameter dish antenna, 14-GHz radio transmitter and 11-GHz receiver, and the network links.
The Universe project is a collaborative venture funded jointly by the United Kingdom's Science and Engineering Research Council and the participating industrial partners. Coordinated by the Rutherford Appleton Laboratory (RAL), the academic sites are Cambridge University, Loughborough University of Technology and University College, London (UCL); industrial partners are British Telecom (BT), GEC Marconi Research and Logic Limited (Logica's US operation is based in New York City).
The prime objectives of the project are to extend the application of packet data transmission procedures suitable for use on highly reliable high-speed LANs to the metropolitan or wide-area networks of the future. The project will also contribute to the establishment of standards for future information technology systems at all appropriate levels of the ISO Open Systems Architecture. Experiments in data, next, image and speech transmission have been carried out on the wide-area network created by the project.
To date, network performance has been close to original expectations. Early problems with the reliability of the earth stations were traced to the practice of switching off earth station equipment during periods when the system was not in use. This was found to be inappropriate, and commercial arrangements to cover maintenance of the travelling-wave tubes had to be modified to enable them to be left switched on.
Early in the project it was decided that the earth stations would be of standard design, and that certain elements of the equipment used to mount the applications experiments would be common either to all the sites or to the sites that would participate in particular experiments. Commonality was a major benefit since it allowed problems to be sorted out at individual sites, and allowed a considerable amount of leap-frogging in extending and elaborating applications.
The economic balances between satellite and terrestrial systems and between circuit-switched and packet-switched networks and their satellite variants will not be able to be determined at an early stage in future commercial developments. Thus, commonality of protocols and flexibility in methods of disposing of traffic provide a significant advantage in enabling a network, or set of networks, to provide the optimum response from the point of view of both the customers and the carrier. Project Universe has shown that such commonality and flexibility can be attained--and experiments in these areas will continue. A Look at Some Key Applications
Key applications mounted on the Universe network include network monitoring and control, distributed computing and file systems experiments, the establishment of distributed videotex data bases, tests of encryption and authentication procedures, and the transmission of digitally encoded voice and image data.
The risk of data interception is particularly acute in a satellite netowrk, due to the broadcast nature of the downlink. Commercial applications will no doubt require protection from unauthorized interception or modification.
The Project Universe encryption experiment (conducted by Logica and MRC) demonstrated the practicality of using the United States Data Encryption Standard (DES) implemented in either hardware or software for the secure transmission of information across a wide-area network. A protocol has been developed that enables the encryption services to be transparent to network applications.
The Universe program provided a unique opportunity to use a wide-area network with several different computer systems linked by a variety of networking protocols into an "open system."
For this project Logica adapted a design for a software support environment that could be distributed beneficially over a LAN. In the design it appeared to each user as if all the tools and resources were local to the user's computer, although in reality they were implemented on various machines throughout the wide-area network. The tools could include compilers, editors, interactive debugging systems and entire run-time environments. Resources included items such as printers, terminals and other peripherals. It was required that this be done for users on a variety of computers and operating systems, and the scope for modifying the system software was severely constrained.
The operation of this framework is coordinated by two central managers, a resource manager and a data base manager. The resource manager acts as a "marriage broker", matching up requests for tools and resources with those known to be free, and handling any conflicts or deadlocks that arise. The data base manager not only controls the movement of files around the network, but also imposes a scheme for accessing files. This means that users can be individually restricted from accessing certain areas, but are also required, for example, to update documentation and specification files if they update program source files.
The implementation of this design under Project Universe was intended as a demonstration, and only a subset of the design was implemented. The framework was put in place for three different machines, the data base manager was fully implemented, and a simple resource manager was built.
The videotex data base created for Project Universe contains summary information about each participant's work within the project. Standard UK videotex and full-screen videotex frame formats are used; information is accessed using a high-speed photo-videotex terminal. Ordinary text frames can also be displayed using a low-cost microcomputer programmed to emulate a videotex terminal. Videotex with Distributed Data Base
The remote access of information from other Project Universe sites is seen as the first phase in providing a videotex service with a geographically distributed data base.
The high speed (on the order of 0.5 Mb/s end-to-end) and intelligent characteristics (such as name servers and bridges) of the Universe network make it significantly different from networks for which Teletex was originally recommended. Additionally, Teletex protocols were originally designed to run on common carrier networks: Packet-Switched Data Network (PSDN), Circuit-Switched Data Network (CSDN) and Public Switched Telephone Network (PSTN). These characteristically have error rates greater than the one in 10 to the ninth power typical of LANs.
Experiments regarding the effect of Universe-type networks on the Teletex service and its communications protocol had three principal objectives:
* to evaluate the Teletex protocols' ability to provide text-transfer services across networks with very different characteristics from those for which it was originally intended. The new networks in this case were the Cambridge ring and the Universe wide-area network.
* To ascertain and solve the problems of implementing the Teletex service in a multi-LAN environment such as that created by the Universe project.
* To verify and evaluate the three very different implementations of the Teletex protocols that were being developed.
Initial tests verified implementations of the underlying network service protocol. Thereafter, tests of the full Teletex software were made, exposing some inconsistencies both in the implementations and in the (at that time) draft Teletex specification. These were successfully resolved and full interworking was achieved between Teletex terminals and an implementation that was complete in high-level software.
The high data rate of the Universe network has been exploited to transfer slow-scan color TV images from a remote site, with reliable control of robots at the same remote site.
An entire frame or a smaller user-selected area can be transferred from one framestore to another. This allows more rapid updating of the main area of interest when transferring a continuous sequence of images; the remaining area can be updated less frequently.
At the remote site, two types of robots are interfaced to microcomputers of the LAN. To provide user control of the slow-scan image transfer and of the robots, a microcomputer receives typed instructions and forwards these in a suitable form to the local framestore or remote robot as required.
The Project Universe network has been used by a simple workstation to access several small picture data bases situated in a variety of locations.
A widely available, low-cost personal microcomputer is used to retrieve and display color pictures from picture stores situated elsewhere on the network. The pictures are composed of text, bitmapped images, graphics orders or combinations of these. The maximum amount of data in a picture is about 16 kilobytes. It takes only a few seconds to connect to the remote picture store, retrieve and display the picture. Pictures could therefore be retrieved quickly and easily from anywhere within range of the satellite whose effective range is the whole of Western Europe and much of Northern Africa. Handling High Data Rates
Experiments have been conducted to discover how the Universe network might extend access to a remote data base held on a computer to include a much greater variety of information types. Stored speech or sound, for instance, might be included within the data, as could graphics and facsimile images.
Such multi-media documents require very high data rates for their effective transmission: a page of text or videotex can be encoded, in say, 1,000 bytes, but it could take 1,000 times that to encode a page of facsimile data into digital form, with a corresponding increase in transmission time.
Communication over the conventional telephone network runs at about only 150 bytes per second. But on a LAN, very high data rates of hundreds of thousands of bytes per second are possible. This means that the transmission of large text files or of digitally encoded facsimile images around such a network could be accomplished very quickly. The limitation with conventional LANs, however, is that they are confined to a relatively small area--within a single building, for example, or just one city block.
The Project Universe network provides a way of extending the LAN concept to cover any geographical area. If LANs are linked by a satellite, then data can be transferred between two LANs (even if they are on different continents) at almost the same rate of speed as is possible within a single LAN. With satellite linkage, large and complex files can be transmitted between any two global points with relative ease and with great speed.
The Universe network has been designed to explore potential problems of the integration of voice, images and data, and to provide simple demonstrations of services based on such a network. Voice experiments include real-time voice communication and the development of speech-compression techniques.
Project telephones have been connected to a Cambridge ring using a simple, inexpensive interface based on a Z80 microprocessor. A specially designed board deals with the conversion of analog speech into digital form using 64 kilobytes per second pluse-code-modulation encoding. The board also handles the telephone dialing conventions. The voice server situated at the Rutherford Appleton Laboratory is based on a GEC 4090 computer and has a file store that can hold up to 30 minutes of speech split into a large number of individual messages.
The system is also linked to the electronic mail system; a mail shot is sent to the recipient whenever a voice message is recorded. The message allows the user to playback individual messages at any time.
Project Universe was the first attempt to extend local-area networking techniques to the much tougher and error-prone environment of wide-area networks, and in particular satellite links. From the start it was decided to implement the applications in parallel with the network, both to prove the network itself and to demonstrate some novel networking applications.
As an experiment it was an almost unqualified success. Many of the demonstrations have subsequently been developed into commercial products, and others have formed the basis for designs and implementations both in industry and academia.
Universe also demonstrated the value of collaboration between industry, government research laboratories and universities, and that such collaboration is cost-effective and contractually feasible.
With the coming availability of low-cost satellite channels and ground stations there will be increasing demand for data links to be handled this way. Project Universe has shown that it can be done.
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|Author:||Smith, P. C.; Hall, V.|
|Date:||Nov 1, 1984|
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