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THE PROVISION OF WIDE-AREA NETWORKING FACILITIES
Dr Barrie J Charles
Joint Network Team of the Computer Board and Research Councils, c/o Rutherford Appleton Laboratory, CHILTON, Didcot, Oxon 0X11 OQX, UK
ABSTRACT
The academic community in the United Kingdom is currently engaged in an extensive programme to provide comprehensive networking facilities within and among the 47 universities and numerous research institutions in the British Isles. The programme is described and the possible provision of similar facilities on an international scale discussed.
1. INTRODUCTION
Since the 1960s, funds for large scale computers in universities and academic research institutes in the United Kingdom have been provided centrally through organisations reporting to the Department of Education and Science. This central funding made possible the establishment of national or regional facilities designed to handle the needs of users which could not be met by an institution's local computing equipment. The distance between these users and the central machines encouraged the early establishment of data communication facilities.
Today the primary requirements for wide-area networks are seen as:
access to large national or regional centres; facility or resource sharing between sites; database access; electronic mail; software distribution; a tool for multi-site scientific collaborations; a means for the itinerant worker to access his home base.
Many of these activities are also now becoming practical internationally and local networks are seen as satisfying similar requirements on a smaller geographical scale. - 241 -
HISTORY
During the early to mid 1970s many separate networks were set up in the UK academic community. These were based either on the packet- switching techniques made popular by the advent of the ARPA network in the United States or on proprietary RJE protocols such as IBM HASP, CDC 200UT or ICL 7020. Growth during the 1970s led to a large increase in the number of point-to-point private lines and a number of arrangements on each site to access each distinct network.
The Joint Network Team was formed in 1979 as the result of the recommendation of a former body set up by the various organisations responsible to the Department of Education and Science. Its objective is to coordinate the evolution of networking so as to arrive at a situation where uniform arrangements are provided to allow any user to access any facility.
THE NETWORK MODEL
The scheme whereby useful network connections can be established without prior development work by the parties involved is now known as Open System Interconnection. To achieve a useful connection there must be an interconnection path between the systems and the systems must agree how they are going to interwork. The interconnection path will be made through one or more networks and the interworking will be achieved by agreeing on the high level protocols (or rules and procedures) to be used for eg, terminal access, file transfer etc.
The model for the provision of networks in the academic community to achieve interconnection between systems is illustrated in figure 1. It is a hierarchical scheme where one or more wide-area networks are used to provide a national system for linking together sites and each site is equipped with one or more local networks. In the short-term, systems on a site may be directly connected to the national network.
Figure 1 - 242 -
To achieve interworking, an agreed set of protocols is required. Protocols are usually built up in layers each forming a separate level of the communications hierarchy. There is now an ISO draft standard which divides this hierarchy into seven layers. These range from the physical layer which describes the electrical connection to the network up to the applications layer which will handle, for example, file transfer procedures. Unfortunately, although there is an international standard on how the hierarchy should be built up there is no accompanying set of protocols to be used for each layer. Because of the timescales associated with such complex international agreements, it is likely to be many years before there is such a complete set.
Using the expertise gained in the early 1970s, a number of protocols have been defined in the UK to fill the gaps left by the lack of international standards. The current complete set of protocols adopted by the academic community for Open System Interconnection is as follows1-6:
CCITT X25 for packet-switched network access; CCITT X3/X28/X29 for terminal access; TRANSPORT SERVICE ("Yellow Book"); FILE TRANSFER PROTOCOL ("Blue Book"); JOB TRANSFER & MANIPULATION PROTOCOL ("Red Book"); ARPA MAIL PROTOCOL ("Grey Book").
The last four protocols are regarded as interim and will be replaced once international standards are firmly established.
4. REALISING THE MODEL
The Joint Network Team has adopted the following approaches to ensure the model is turned into a practical reality:
1. The placement of development contracts for machine protocol packages and network components: the resultant products are then installed widely in the community using centrally-provided funds;
2. The protocols are included as mandatory items in Operational Requirements for all new major computing systems to encourage the provision of manufacturer support;
3. Detailed technical advice is given to the providers of services and the funding bodies in the evolution of communications arrangements; - 243 -
4. Collaboration within the community is ensured by way of workshops,
meetings, committees etc.
5. THE CURRENT STATE
National communications are currently provided by two separate
wide-area networks: the public packet-switched network (Switchstream 1
or PSS) and the private X25 network set up by the Science and
Engineering Research Council (SERCnet). These two networks are
interlinked by a gateway which can ensure communication between a system
on one network and a system on the other. There are currently 25 X25
connections to PSS from 25 community sites and around 100 connections to
SERCnet from about 55 sites. Approximately 20 different types of system
are connected.
The provision of local area networks is at a somewhat earlier stage
of development. Local X25-based communications are generally being
supplied using GEC 4000 based Campus Packet-Switching Exchanges and
terminal concentrators (PADs) supplied by Camtec Electronics. Service
networks of this sort are now installed on 7 campuses and planned for 16
further sites. Cambridge Ring ("Slotted Ring") networks are currently
installed at 3 institutes and planned for 8 further sites.
The following systems have been connected to these networks and in
general support most of the protocols listed above:
Honeywell/Multics DEC10/TOPS10
Honeywell/GCOS DEC20/TOPS 20
IBM/VM VAX/VMS
IBM/MVT VAX/UNIX
IBM/MVS PDP-11/UNIX
CYBER/NOS PDP-11/RSXllM
ICL 1900/GEORGE 3 PDP-ll/RT-11
ICL 2900/VME LSI-ll/RT-11
PRIME/PRIMOS
GEC 4000/OS4000
Most of the packages are in a form suitable for installation at
other sites and are supported either by manufacturers or by universities
under contract to the Joint Network Team.
Figure 2 shows an example campus, the University of Exeter, with
X25-based local communications. Terminals connected to PADs can access
either local hosts connected to the X25 switch or (via the gateway) any
host connected to SERCnet or PSS. International access is also possible - 244 -
Figure 2
Example Campus - University of Exeter
ICL
through the connections between PSS and the public networks in other countries. File transfers can be initiated between local machines and remotely, and jobs prepared on one machine (the ICL System 4 or the PDP- 11 UNIX) are routinely submitted for execution elsewhere (eg on the ICL 2900 or SERCnet hosts respectively).
6. CONCLUSIONS FROM UK EXPERIENCE
The UK academic community is implementing an open networking system which, although there is still much work to be done, already works. The following benefits are starting to accrue:
flexibility in choice of new systems (because customers are not tied to one manufacturer); flexibility in assigning users to systems; reduced requirements for applications software by moving users, not software; effecting economies and bringing a versatile terminal closer to the user by divorcing terminals from systems; removal of media translation problems (file transfers over the network replace costly extra peripherals); improved human communications through electronic mail.
There are of course several problems associated with the approach. The lack of firm international standards has forced the community to develop much of its own software with the corresponding costs, long lead times and heavy support requirements. The evolution of protocol standards means that this commitment will continue for some time. How to ensure protocol conformance is also a problem which seems a long way from solution. - 245 -
The fluidity in the Local Area Network scene has also been a cause
for concern with user expectations far in advance of standards and
products. The separation of the user's terminal from the computer by
the network is also causing difficulties, particularly with some Digital
systems where single character input with echoing by the host is
essential.
However, despite these problems, we feel that essentially the right
decisions have been made and that the UK academic community is now
moving into the new era of "téléinformatique" with much of the ground
work done.
7. INTERNATIONAL COMMUNICATIONS
Public X25 networks are now becoming available in many countries:
an indication of those accessible from the UK is given in table 1. Many
of these networks are interconnected to provide an international packet-
switched service. This means that it is now practicable for computers
in different countries to communicate through the medium of an X25 call.
The general acceptance of the X3/X28/X29 protocol means that many hosts
will also offer a useful end-user service for terminal access. Slight
incompatibilities between the interpretaions of X3/X28/X29 may however
degrade the quality of the user interface offered.
Internationally approved protocols offering file and job facilities
are still many years away, however. ISO does not expect to come up
with draft proposals before 1984. This means that implementations are
unlikely to be available before 1986 even if these timescales are kept
to (ISO's track record is not good). The CCITT recommendations for
Télétex can be used for electronic mail although they are not well
suited for message exchange between computer-based message systems.
Table 1
International Connections From UK
AUSTRIA FINLAND NORWAY SWITZERLAND BELGIUM FRANCE PORTUGAL USA CANADA GERMANY SINGAPORE DENMARK HONG KONG SPAIN EURONET JAPAN SWEDEN
COUNTRIES TO BE ACCESSIBLE BY END 198 2
The UK is not alone in adopting interim high level protocols and
useful international facilities may be provided through the use of
protocol convertors. The European Committee for Future Accelerator's
working group on data processing standards, sub-group 5, has been - 246 -
looking into the possibilities for harmonising comrrunications among
high-energy physicists. This could involve the development of protocol
conversion services and the promulgation of additional HEP protocol
recommendations.
ACKNOWLEDGEMENTS
The author played only a small part in the work described in this
paper which was accomplished through the efforts of many people in the
academic community, some manufacturers, his colleagues in the Joint
Network Team and through the support of the funding bodies and other
organisations.
REFERENCES
1) British Telecom Technical User Guide 17 (November 1980).
2) Character Terminal Protocols on PSS (Revision 1), SG3/CP(81)6, Study Group 3 of British Telecom PSS User Forum (Feb 1981).
3) A Network Independent Transport Service, SG3/CP(80)2, Study Group 3 of British Telecom PSS User Forum (Feb 1980).
4) A Network Independent File Transfer Protocol, FTP-B(80), High Level Protocol Group, as revised by the File Transfer Protocol Implementors' Group of the Data Communication Protocols Unit. (Feb 1981).
5) A Network Independent Job Transfer and Manipulation Protocol, DCPU/JTMP(81), The JTMP Working Party of the Data Communication Protocols Unit (September 1981).
6) JNT Mail Protocol, C J Bennett, Department of Computer Science, University College, London (Jan 1982).
References 1-3 are available through PSS Marketing, 5th floor, Seal House, 1 Swan Lane, London EC4R 3TH.
Reference 3-6 are available from the Joint Network Team, c/o Rutherford Appleton Laboratory, Chilton, Didcot, Oxon 0X11 OQX,
* * *
QUESTIONS
MR. R. DOBINSON CERN
• Q —> What speed do present campus-wide networks run at ?
• A —> The present maximum is 48 Kbits/s. This allows a surprisingly high activity.
MS. P. RIMMER CERN
• Q —> Do you foresee proprietary difficulties when offering network access to facil• ities like software packages which have been purchased as single copies? - 247 -
• A —> So far the problem has not come up seriously. The problem might however, arise in the future. For example, the UNIX licensing charges are proportional to the number of terminals with potential access; that might be difficult to estimate and monitor.
MR. W. MITAROFF INST. F. HOCHENERGIEPHYSIK VIENNA
• Q —> As long as file transfer protocols do not exist, do you think it reasonable to use an existing serial standard, adding some tricks. The host might well consider your local mini as a terminal, but locally information could be assembled on disk, using e.g. an X-11 interface.
• A —> This is certainly possible, but many limitations would arise that either de• grade the user service or have to be overcome by more and more 'tricky' software: - Interspersed random messages to the terminal, - Flow control problems at the terminal end or with an overloaded host, - Restrictions of character sets for transmission, impossibility of binary files, - Necessity to synchronise transfers with terminal use, i.e. no batch mode, - Poor user interface.
MR. R. MARTY INST. F. INFORMATICS, UNIVERSITY OF ZURICH
• Q —> Have you done any work on standardising network-wide name servers?
• A —> Only in LAN-s, like the Cambridge Ring. Country-wide name servers will first be implemented as manual 'registration service'.
MR. J.M. GERARD CERN
• Q —> Is it really your intention to connect terminals via networks and Triple-X rather than by circuit switching?
• A —> Yes, in principle.
MR. M. TURNItL BNOC GLASGOW
• Q > The attachment of all graphics and full-screen facilities directly to X-25 type networks might lead to overload. Would it not be safer to provide these facilities lo• cally, using full networks only for long-distance communications.
• A —> Yes, that is indeed an alternative.