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The capital cost of the telex system per subscriber line is very much greater than for a telephone system of the same size mainly because of the high cost of the teleprinter terminal compared with that of a telephone terminal. Since capital charges play an important part in determining rentals, the rental charged for telex subscriber service is much higher than for telephone service. Consequently connection to the telex system is generally not justified unless the subscriber has a line loading much higher than is usual for a telephone subscriber. This affects trunking of telex switching systems which must be designed for heavy subscriber loadings. Historical Background of Telex Service Historically, subscriber-operated teleprinter switching systems awaited the development of a reliable and inexpensive teleprinter suitable for use in widely dispersed subscribers' offices. The start/stop principle was used in the 1920's in the United States and Europe to develop such teleprinters, which resembled an office typewriter in operation and required a minimum of auxiliary equipment. Large telegraph switching networks developed in the 1930's. using these newly-developed start/stop page printers. The first of these was established by the Bell system in the United States in the year 1930. This network used direct current subscriber loops and voice frequency telegraph trunk connections and was designated the TWX system. This system continued to grow as a manual network until, by 1962, it had approximately 60,000 subscribers. The network in this year was converted to automatic operation through partial integration with the telephone switching system using tone signalling subscribers terminals. In Europe fully automatic switching networks operating on a telegraph basis had been developed in the thirties, the first of these being the German network using the well known dial selection "neutral" supervision step-bystep switching technique which was followed later by many other countries. The Netherlands developed an automatic switching system for telegraphy using the common control switching technique and with the then novel feature of the use of the keyboard of the teleprinter for selection. Further the system provided for printed service code indications to be sent to the calling subscriber's machine as part of the supervisory signalling of the system. In Australia the two main lines of overseas development were examined • that of the Bell system in the United States toward integration with the telephone switching network using tone signalling terminal units with the teleprinter, and • that of the rest of the world, toward internationally compatible automatic teleprinter switching networks using exclusively telegraph trunks. The decision was made to adopt the latter course. Important reasons for this decision were that the Australian automatic trunk telephone network was some years behind the degree of automatisation achieved by the Bell system and automatic teleprinter switching on this basis would not have been possible on many routes for some years. Predominantly long distance telex traffic 20
would have represented a heavy increment of load on telephone trunk routes and substantial additional capital investment. The United States' regulatory and competitive situation in telegraph communications was also thought to be an influence affecting the type of service provided there. In 1948 the C.C.I.T.T. (The International Telegraph and Telephone Consultative Committee) had begun to draw the two separate lines of European development together in formulating standards which have been progressively extended with successive C.C.I.T.T. meetings, and the Australian system has been designed to closely follow these standards. In four respects the standards allow of no alternative. These are • standardisation of the speed of transmission at 50 bauds. • standardisation of teleprinter keyboard arrangements such that these must be in accordance with International Alphabet No. 2. • standardisation on the principle of unattended reception with automatic answer-back verification. • standardisation on the important principle that for international circuits the outgoing country should conform the signalling of the incoming country. In other respects the C.C.I.T.T. drew up standards which allowed specified alternatives. The most important of these are • the method of selection from the subscriber's machine which may be either by dial or from the keyboard of the machine. • supervision of call progress at the subscriber's machine which may be either by printed service code or by visual indicator. • the trunk signalling technique employed which may be one of three types. In Australia, planning for an automatic telex service started in the late 1950's and, together with the Overseas Telecommunications Commission (Australia), specifications were prepared during the early 1960's for an internal system to be provided by the Post Office, and for an international gateway exchange to be provided by the Commission. The Post Office and the Commission, after examining tenders sought throughout the world, placed matching orders in 1962 for equipment from L M Ericsson. The Commission's international exchange commenced operation in September 1965, the Post Office internal network commencing service in June 1966 with approximately 2,500 subscribers. This network has since grown to approximately 3,200 subscribers. Characteristics of Australian Telex Service Telex is a service used primarily by industrial and commercial organisations and has a smaller penetration than the telephone service. Development studies show that it is most probable that there will be about 5.000 subscribers in the whole of Australia by 1970, increasing to about 11,000 by 1980. Compared 21
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