ABSTRACT
Strowger automatic switching had been the standard technique employed in the British telephone system since the 1920s. By 1946 the Post Office was considering what type of exchange switching should replace it. Its disadvantages in a telephone system which was to become increasingly heavily used were that it had a high maintenance requirement, required a large amount of switch and trunking equipment and was a relatively slow method of switching.
The maintenance requirement was an undesirable feature, because it meant that the engineering costs of running the system were likely to grow as fast as the total traffic carried. The bulky nature of the switching equipment meant that Strowger was expensive to provide and that the exchange buildings which had to be found in crowded city centres needed to be fairly big and to contain provision for expansion. The slowness and inflexibility of switching affected the capacity of the line network and made the addition of new subscriber facilities difficult to achieve.
Agreements existed between the Post Office and its exchange equipment suppliers for the conduct of research on a co-operative basis. A formal procedure for bringing about technical change had been evolved; joint decisions of the Post Office and the five exchange manufacturers were discussed within the British Telephone Technical Development Committee, and the work necessary to develop new equipment was allocated to individual corporate members. The basic structure of the BTTDC was used for the development of the new exchange techniques on which the Post Office had started work in the late 1940s. The committee structure was adapted and a new research agreement was established specifically for the exchange project.
The main functions of the BTTDC were to rationalise and make the best use of research facilities, and to ensure that agreement was reached on common standards and technical specifications for telephone developments. Its method of functioning was to produce a consensus on the nature of marginal improvements to the established Strowger switching methods. It was not suited by its constitution to the resolution of conflicts on issues when real grounds existed for conflicting technical opinions, and where exploratory development and some open-ended research were needed to99 establish the technical parameters affecting the choice of a wholly new technique.
The indications were that the Post Office had made up its mind on the choice before negotiatons with the manufacturers began. The system the Post Office favoured, time division multiplex, used electronic valve switching. It was a technically elegant solution with a large amount of common equipment and the advantages of reliable components, fast switching and space saving. Its economy in the use of equipment might have produced low capital costs if it had become fully developed. Its disadvantages were that its high degree of technical sophistication made it inflexible and created major difficulties of inter-working with the rest of the system.
Development of time division multiplex under the Joint Electronic Research Agreement did not provide conditions in which a number of experimental solutions to the problem of the choice of a new technique could be evaluated. Work on the alternatives by manufacturers was restrained, being carried on outside the context of official agreements, and it was not until 1960 that other systems were given serious official backing. The result was that, when new types of exchange were needed in the mid 1960s for installation in the larger type of exchange applications, neither time-division multiplex nor the reed-relay system which succeeded it were ready.
To fill the gap the Post Office decided to install crossbar exchanges, a type which had not been included in the development programme. Crossbar switching employed electro-magnetic techniques instead of electronic ones. The types of exchange installed in Britain were adapted from models developed by the manufacturers for other markets. They were not ideally suited to the British system, their main disadvantage being that, having been developed without Post Office participation or the expectation of use in Britain, they did not include the features which the Post Office regarded as desirable.
As a result of the unsuitability of crossbar systems as developed, the Post Office had only a restricted choice available when it came to make a committing decision on techniques in 1972. By that time reed-relay exchanges for large applications were within two or three years of commercial service and the Post Office had to decide whether to make a further commitment to crossbar exchanges or to invest in the further development of the reed-relay system as the major exchange type of the future. Detailed study of the reed-relay and crossbar types available showed the former to be more suitable. Since the Post Office had never sponsored the development of a crossbar exchange ab initio, the types available for comparison with reed-relay had features and design philosophies which would have required more fundamental and more costly development to make them suitable for use than was involved for the reed-relay design. It may well have been the case that the technical merits of the reed-relay design were superior to those of the crossbar. Both systems are widely used by foreign telephone administrations. But the choice in the Post Office’s decision was determined more by the absence of official sponsorship of a crossbar system than by competitive evaluation of the alternatives.
The Post Office’s interest in research on new types of capital equipment can be traced back to the beginning of the century. Having assumed responsibility for the trunk network before 1900, it had promoted the development of new types of cable. Laboratory facilities were built up in100 central London and in the early 1920s the research station at Dollis Hill was set up. Post Office work on transmission techniques, particularly in connection with under-sea cables, had achieved for it an international reputation. This tradition was well maintained in postwar years and extended into satellite transmission.
There was a strong professional association of Post Office engineers. Its Journal, published regularly since 1906, constitutes virtually a complete record of Post Office research down the years. Prior to the electronic exchange, the Post Office had been content to allow manufacturers of exchange equipment to lead in exchange development. The industry had in fact not been well established in Britain until after the First World War and Britain tended to follow technical developments elsewhere, rather than to lead. In the first major decision on automatic exchange types, taken between 1918 and 1924, a policy of testing alternative exchanges in commercial installations from a number of manufacturers had been followed.
What is interesting about the story of the electronic exchange is that the relationship between the Post Office, as the only large domestic customer, and the equipment manufacturers who made up the supplying industry had been developing over a period of thirty years before the joint agreement on electronic development was made. There was early recognition of the dangers of the market structure which existed – that uneven loading of the capacity of the manufacturers might result from the single customer phasing its orders or favouring one supplier to the exclusion of others. The arrangements made for market-sharing also took account of the responsibility of the Post Office for technical development. As the only large domestic customer it would have a determining influence upon what new techniques were adopted and when they were brought into use, while the industry would have the job of developing them and manufacturing new equipment. In recognition of this responsibility, the Post Office undertook to agree with the industry on the technical changes that were desirable and necessary.
It would be obtuse not to recognise here that the BTTDC represented sincere effort of a pioneering nature to deal with a genuine problem. The economic waste to the Post Office and the industry of having different techniques developed by each manufacturer, and then of one being chosen, appeared a serious consideration. Added to that, companies might be forced out of business by competitive development, which could damage the economy. However, the agreements made between the two sides failed to recognise that on some occasions competitive development was the only way to make a valid evaluation of alternative techniques. By cutting out wasteful competition, they almost succeeded in abolishing the analytical procedures needed to make a choice between techniques.
