Standards issues in data communications Gregor V. Bochmann The lack of development in There is a long history of international standards in telecommuni- standards and compatibility in the cations because of the necessity of obtaining compatibility between field of data communication and different national networks. In the data communications and processing requires urgent processing areas, however, standards and compatibility are much less attention. The author discusses the developed: data communications have long been a secondary aspect compatibility issues that arise from of data processing, and large computer manufacturers tend to try to the introduction of packet- sell total data processing systems, so that intersystem compatability is switching networks, which typify not needed. However, with the increasing cost of software the growing interdependence of development, compared to hardware costs, there is a growing user computer and communication technologies. Focusing on Canada need to share software modules and thus avoid the duplication of as a case example, he examines development costs. Compatibility, therefore, is an essential condition issues relating to the compatibility for the realization of the large-scale applications of data between the communication communications and processing that will soon be technically services offered by different feasible.’ networks and communication functions used for distributed data processing, and also between the Background procedures employed to provide The area of data communications is characterized by a growing these services and functions. symbiosis between communications and computer technology. Data The author is in the Departement communication was first used in teleprocessing systems, where d’lnformatique, Universite de computers and terminals were connected through leased or switched Montreal, 2900 Edouard-Montpetit, telephone channels over which data were transmitted. Gradually, the Montreal, Quebec, Canada. data processing systems incorporated more and more sophisticated communication functions and the carriers relied on digital .and ’ International implications of computer computerized techniques for building their communication networks. communications and possible future developments are discussed by I. de Sola A typical example of the interdependence of computer and Pool, ‘International aspects of computer communications technologies can be found in packet-switched data communications’, Telecommunications networks. The first network developed on this principle was the Policy, Vol 1, No 1, 1976, pp 33-5 1. ‘Funded by the Advanced Research ARPANET.* The principle of packet-switching consists of Projects Agency (ARPA) of the US subdividing the data to be transmitted into a number of packets with a National Defence Department, the maximum length of several hundred characters, and sending these ARPANET was the first large-scale experience with packet-switched data packets independently through the network. Therefore, the physical transmission. Still operational, it allows transmission circuits between the nodes (switches) of the network resource sharing between a large number (built of mini-computers) can be shared between many different users. of computer centres in universities and research centres. The main objectives and Based on this principle, a ‘datagram’ facility was subsequently characteristics are described by L.G. proposed as a service to be provided by public data networks. Roberts and B.D. Wessler, ‘Computer It has been shown in the French experimental network Cyclades3 network development to achieve resource sharing’, Proceedings AFIPS, 1970. pp that such a datagram service can be used advantageously for 543-549. establishing reliable communication between application programs in TELECOMMUNICATIONS POLICY December 1977 Statdurcfs issues it? data cottmutzicutiotts host computers and terminals connected through a packet-switched data network. However, for the first generation of services to be offered over the new packet-switched public data networks,4 the carriers chose what are known as ‘virtual circuits’. Virtual circuits resemble real switched circuits in many respects, but the service is charged essentially by the number of packets transmitted (not by connect time). At the same time, several computer manufacturers have developed complex communication hardware and software for building networks of computers and terminals connected through leased or switched circuits. Independently, manufacturers are also developing new kinds of terminals for different applications. It is very common to find strong incompatibilities between the interfaces for terminals and computer systems of different manufacturers and between those interfaces and the new access protocols for public networks. Much effort will be needed to obtain more compatibility and agreed standard interfaces. Canada will be the first country to have two independent public packet-switched data networks. For several years now, leased digital circuits have been available from two competing common carrier groups, the Trans-Canada-Telephone System (TCTS) and CNCP Telecommunications. Both groups will now provide new data communications services: TCTS has built the Datapacs network, to provide packet-switched virtual circuits with a network access protocol compatible with the standard X.25 of the International Telegraph and Telephone Consultative Committee (CCITT). CNCP is building the Infoswitch network which incorporates Infoexchange, a digital circuit switched service; Infocall, a service of packet- switched virtual circuits for transparent packet transmissions; and Infogram. a service of packet-switched virtual circuits similar to those provided with the CCITT standard X.25. In addition, both networks provide for the handling of simple character-oriented terminals, such as teletypes. and other terminal equipment. The focus of this article is on the compatibility issues that arise from the introduction of packet switching. Other important issues are 3 Building on the experience gained with the ARPANET, the French Cyclades therefore not considered, such as those related to pulse code network has contributed much to the modulation (PCM) for telephony, digital switching, integrated development of packet-switched data services networks (INS), or satellite broadcasting. communications. Its major fealures are described by L. Pouzin. ‘Presentation and major design aspects of Cyclades Need for network interconnection computer network’, paper presented at 3rd Data Communications Symposium. Tampa, Florida, November 1973. Interworking of several data networks is essential for international 4The French and British PlTs. the US communication through several national data networks. In this case, Telenet corporation and the Canadian each of the user’s computers or terminals, also called ‘data terminal TCTS were the main proponents of the virtual circuit service for .public packet- equipment’ (DTE), can directly access only the network of the switched data networks. The CC1l-r has country in which it is situated. Communication between two DTEs in adopted Recommendation X.25 for this different countries necessarily involves interworking of networks. service in its plenary session of 1976. Several public networks providing such a The situation is different when several networks cover the same service are being planned (eg France, geographical area, as do the two Canadian networks. There is Japan, and the UK) or are already working competition between the networks, since the user’s DTEs could be (Telenet (US), Datapac and lnfoswitch (Canada)). connected to either. Two DTEs connected to different networks can 5W.W. Clipsham, F.E. Glave and M.L. communicate only if there is an interconnection between the two Narraway. ‘Datapac network overview’, networks. On the other hand, two DTEs connected to both networks paper presented at Third international Conference on Computer Communi- could communicate through each, possibly using one as a back-up cation, Toronto, Ontario, 1976. facility. 382 TELECOMMUNICATIONS POLICY December 1977 Starldards issues b data communications 6Telenet corporation proposes the use of Interworking of packet-switched data networks is a field in which a variant of the X.25 protocol for considerable research and development are underway. Such work is interconnection of packet-swTtched data networks (L.G. Roberts, ‘International necessary to determine the appropriate scheme of interworking for the interconnection of public packet- applications described above. Different schemes have been proposed6 networks’, paper presented at Third and several have been tried out.’ All use some kind of ‘gateway’ that international Conference on Computer Communications, Toronto, Ontario, implements the connection between two networks through which user 1976). This approach, however. has data as well as control and administrative information are exchanged. drawbacks and other approaches for For distant international communications, the user data may pass interworking of packet networks have been proposed and/or implemented (V. through several such gateways involving one or more intermediate Cerf, A. McKenzie, Ft. Scantlebury and H. data networks. A typical situation, including a country with two Zimmermann, ‘A proposal for inter- national data networks, is shown in Figure 1. The figure also shows network end-to-end protocol’, IFIP WG 6.1, General Note 96, September 1975: an ‘international’ network providing long-distance