UNINETT is a Norwegian national packet switched network established through a joint effort between the Norwegian Universities, some research institutions and the Norwegian Telecommunication administration. The network is based on the CCITT recommendation X.25 and some UNINETT specific higher level protocols. Work will be continued in order to adapt the network to forthcoming international communication standards. For instance, the current UNINETT hierarchical model will soon be changed so as to conform to the ISO proposal for Open Systems Interconnection. The network topology and system design is described, together with existing higher level protocols. Some experiences with the project work as such is also reported.
II. INTRODUCTION
During 1975 representatives from the computing centers servicing the four Norwegian universities and from the Norwegian Telecommunications Administration agreed to establish data network services for the universities and for some research institutions. A UNINETT project group was formed with participants from these institutions and some Norwegian computer manufacturers. Specifications for a packet switched data network were developed, and the network was brought into operation in 1979. Until now, about one million dollars have been spent on the project as a whole.
UNINETT covers two aspects
* Local data network within each university campus.
* A national network for the exchange of services between the universities.
The inter-university traffic is handled by an experimental packet switched service, called NORPAK (Norwegian Packet Switched Service), run by the Norwegian Telecommunication Administration.
The local networks are connected to the NORPAK service via the Nordic Public Data Network. The local networks vary in configuration and complexity.
III. UNINETT AS PART OF AN INTERNATIONAL NETWORK COMMUNITY
The NORPAK-service will by mid-1980 be connected to a Swedish public packet switched service called "SWENET". The SWENET service will have further connections to Finland and Denmark. An international data centre in London (IPSS) will connect the NORPAK-service to a worldwide packet switched network, and the UNINETT users will have access to a variety of international network services.
Computer networking is an area in which cooperation is more than usually important in order to promote international standards. UNINETT realized this at an early stage, and much effort has been spent on keeping up with the work on international standards agreements. We believe this will turn out to be beneficial when the national networks are being interconnected.
IV. THE UNINETT OPEN SYSTEMS ARCHITECTURE
Classical data processing centres very often form "closed" information processing systems with few, if any, possibilities for information exchange between them. As opposed to such systems, common terminology defines an information processing system to be "open" when it is connected to a transport mechanism common to other information processing systems, as described in fig. 2.
Hardware and software incompatibilities between the various information processing systems, make it necessary to define system independent methods for the information exchange. Such distributed systems are usually designed so as to form a layered structure. A layer in one open system cooperates with a layer in another open system according to a set of rules called a protocol, and it offers a set of network services to the next higher layer in the hierarchy. The architecture of the distributed system is defined by the set of services offered by each layer, and the protocol within each layer.
The UNINETT open system is based on a 5-layered model as a framework for protocol development (see fig. 3).
The three lower layers of the UNINETT model, called the Network module, provide "error free" data transmission and sequence and flow control on the transmission. The transport service is based on packet switching techniques as defined by CCITT recommendation X.25 (Ref. 13).
The protocols on the Service Layer offer application oriented services to the Open System processes.
The levels may be used to form network modules like gateways, terminal concentrators, resources and switches. These may form, for instance, a local network (Ref. 9) with a gateway to another network as shown in fig. 4.
V. THE UNINETT HIGHER LEVEL PROTOCOLS
Application oriented protocols offer specialized network services to UNINETT users. Efforts have been made in order to make these protocols as simple as possible without loss of generality. All the higher level protocols have a common set of transport service requirements. The protocols are however so designed as to allow for adaptability to other transport services than those specified by UNINETT.
The following network services have been fully specified:
- An interactive service enabling human users to communicate with applications on network resource computers (Ref. 6).
- A file transfer service extending the file copy service over the network such that bulk data may be transferred between the various host computers (Ref. 8.).
- A mail service for transfer, storage and delivery of textual messages among users of the network.
Plans also exists for the inclusion of a remote batch service.
The UNINETT Interactive Protocol (UIP) applies to a scroll-mode rather than a page of forms oriented terminal. UIP is intentionally designed very similar to CCITT recommendation X.29, bearing in mind the possibility of building a single station which can handle both protocols.
The UNINETT File Transfer Protocol (UFTP) has been designed after careful studies of existing protocols, in particular those of EIN, ARPA, EPSS and Cyclades. The resulting protocol generally enables equivalent services with a less complicated scheme for the exchange of file transfer control messages.
The UNINETT Mail Protocol (UMP) may very well be looked upon as input to the ongoing work within CCITT on a standard protocol for TELETEX.
VI. STANDARDIZATION ON OPEN SYSTEMS INTERCONNECTION
Development of complex computer networks is mainly a question of standardization. The UNINETT higher level protocols are examples of "standards" for the Norwegian university community agreed upon by all the participating institutions.
The CCITT recommendation X.25 was adopted at an early stage as a coming standard for packet switching on the lower levels. This turned out to be a wise choice, as X.25 seems to be becoming widely accepted (Refs. 2-5) .
The UNINETT reference model has been extremely important as a common agreed framework for the specification of network protocols. The same approach has been taken within the International Standardization Organization (ISO Technical Committee 97/Subcommittee 16) on its work on Open Systems Interconnection.
The ISO model has 7 layers as shown on Fig. 5, as opposed to UNINETT's 5 layers. The UNINETT model is now being revised in order to bring it as close as possible to the framework for future international standards.
Fig.5. ISO-model versus UNINETT-model
VII. THE UNINETT JOB CONTROL LANGUAGE
The lack of standardization of job control languages is one of the main user problems in a network environment. It is in fact a real barrier against gaining full benefit from a diversity of network resources.
We have, therefore, made a proposal for a UNINETT Job Control Language (UJCL) (Ref. 7). This should be the end user's interface to the UNINETT computer network.
The purpose of the UJCL is to
- present the services offered by the UNINETT system in a soft and user oriented way
- smooth out some of the differences between the various operating systems.
Compared to ordinary Job Control Languages, the ambitions have been set very low. A kind of local self-government has been the guideline, in which only features involving more than one operating system will be subject to UNINETT processing.
VIII. PROJECT EXPERIENCES
Gathering research organizations, the Universities, the Computer Manufacturers and the Telecommunication Administration in one project has turned out to be advantageous to all the participants. In joint efforts of this kind, questions marked by prestige and diverging vendor or PTT interest often tend to make successful cooperation difficult. In the UNINETT project, we have mostly experienced the opposite effect.
First of all, the numerous project meetings and test-hours spent together by the participants, have established links across institutional borders which have brought the institutions as such closer together.
The Norwegian Telecommunication Administration has shown great interest in the project, and quite unlike international practice, has been very sympathetic to views and wishes from the other project participants. The Norwegian Telecommunication Administration participates in the standardization work within CCITT, and during the project period they have ensured that the other UNINETT members have always been updated on the latest achievements within this work.
The manufacturers participation has led to expedited delivery of necessary hardware (e.g. HDLC-interfaces, described in Ref. 10)
Some practical experiences with the implementation work are also worth mentioning. With one exception, all network software were written in higher level languages (SIMULA, PASCAL, MARY). In the early stages of program and protocol debugging, simulation methods were also applied to some extent (Ref. 11) . All this has shown great advantages as to the time spent on implementation work.
Each of the participating institutions have implemented its own version of the network modules with differences in hardware, monitor and language. The result is a widespread knowledge of how to implement network functions. A coordinated implementation scheme could however have lead to an earlier completion of the network as a whole.
One member bought the UNINETT specified software from a large computer vendor. This seems to have been an unwise choice, both because no competence on the actual implementation was established at the institution involved, and because the coding was performed in a low-level language on a micro-computer with very few debugging tools available.
IX. SUMMARY
The hierarchically structured UNINETT Model has been very useful as a conceptual framework for discussing networking problems and implementations. The model, although it was designed quite early, shows similarities to the Open Systems Architecture specified by ISO TC97/SC16.
A transport service based on X.25 has been implemented. A Transport Station on top of
X.25 expands the addressing space.
On top of the Transport Service the following Higher Level Services have been specified and are now under implementation.
- UNINETT Interactive Protocol (UIP) is a virtual terminal protocol offering interactive services.
- UNINETT File Management System contains a File Transfer Service.
- UNINETT Mail Service.
X. REFERENCES
[1] J.E. Engebretsen: Description of the UNINETT Functional Levels, UNINETT report no. 1, Oct. 1976.
[2] A. Asphjell et al: Interpretation of the CCITT Recommendation X.25 Link Level Procedure, UNINETT report no. 2, Jan. 1977.
[3] A. Asphjell et al: Implementation of the CCITT X.25 Link Level Procedure, UNINETT report no. 3, April 1977.
[4] K.A. Bringsrud, T. Larsen: SIMULA Description of the Link Level Procedure, UNINETT report no. 5, Dec. 1977.
[5] D. Belsnes et al: Description of Packet Level and Transport Station in the UNINETT Network Module, UNINETT report no. 4, June 1977.
[6] E. Lynning: UNINETT Interactive Protocol, UNINETT report no. 7, May 1979.
[7] T. Amble: UJCL - A Proposal for a UNINETT Job Control Language, UNINETT report no. 9, Nov. 1979.
[8] D. Belsnes et al: UNINETT File Transfer Protocol, UNINETT report no. 10, 1980.
[9] J.E. Engebretsen, A. Engdal: The Use of the CCITT X.25 Recommendation in a Local Network, Proceedings of the European Computing Congress 1978 (Online).
[10] H.G. Endresen et al: Microprocessor-based Hardware for driving an X.25 link, Proceedings of the European Computing Congress 1978 (Online).
[11] D. Belsnes, K.A. Bringsrud: X.25 DTE Implemented in SIMULA, Proceedings of the European Computing Congress 1978 (Online).
[12] W. Jensen, J.E. Engebretsen: A Basic Functional Data Network Architecture, Proceedings of the Teleinformatics' 79 Conference (IFIP), June 1979.
[13] CCITT Recommendation X.25: "Interface Between DTE and DCE for Terminals Operating in the Packet Mode on Public Data Networks", Orange Book, Vol. VI 11.2, Public Data Networks, ITU, Geneva, 1977.
[14] "Reference Model of Open Systems Interconnection", Version 4, June 1979. ISO/TC97/SC16/N227.
Egil Kommedal:
Egil Kommedal is head of the research group for Data Communication in the Norwegian Telecommunications Administration Research Establishment. Since joining the Telecommunications Administration in 1975 he has mainly been engaged in development of Norwegian and Nordic packet switched data transmission services and other new telecommunication services, in particular teletex and videotex.
Alt Engdal:
Alf Engdal has a degree in cybernetics from the Technical University of Trondheim. Since 1971 he has been engaged as a research scientist at the University's Computing Centre.For the last two yaars he has been project leader for UNINETT, a joint effort by various Norwegian Institutions to establish an experimental packet switched network.
Kjell Age Bringsrud:
Kjell Age Bringsrud earned his MS. degree in Computer Science at the University of Oslo. Since 1971 he has been employed by the EDP-Centre of this university, participating in the work of implementing SIMULA on CDC computers. He is currently engaged in data communication projects.