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to be tripped. The calling subscriber's "answer-back", which includes the subscriber's number, is used for identification purposes because these calls are not periodically metered at the originating exchange, as are national calls, but are toll-ticketed at the international centre. The Commission is thus able to present an itemised account for this high-rate international traffic. This ticketing process is manual, but eventually the function will be automatic and calls will then be established completely automatically on some routes. Following receipt of the calling subscriber's "answer-back", the international exchange sends the printed service code GA to the calling subscriber as an indication that he may now key the international number. The call then proceeds in much the same way as for a national call. For international inward calls the international exchange is treated as though it is a service position connected to the Sydney national telex transit exchange and 5-digit selection information, preceded by the usual "Figures Shift" register opening character, is fed into the national telex exchange register to set up the call in the usual way. Subscriber Terminal Equipment As part of planning for the introduction of automatic telex service, the Australian Post Office studied teleprinters submitted against a Post Office specification from manufacturers all over the world. Finally the well-known Siemens T Type 100 page printer was chosen as the standard machine for the telex service and was introduced into the network in early 1960, with the intention that by the time the telex network was automatised, all machines would be of this type. The machine, as offered, simplified the design of the subscriber's terminal control unit since the machine itself incorporates calling and clearing keys and circuit features such as centrifugally operated contacts in the machine to prove that the motor is running. Among the optional features of the machine is the ability to add attachments such as a tape reperforator enabling incoming line signals to be copied on perforated tape, or for information to be prepared in both page and tape form as an off-line process using this machine. Also available is a tape transmission attachment and more than 50 % of all Australian telex subscribers hire machines incorporating both these attachments. The terminal control units designed by the Post Office have two functional arrangements. The first of these is for machines without tape reperforation and transmission attachments and, in the case of single current signalling units, uses a very simple 2-relay control unit which is incorporated as part of the machine. For machines having tape attachments, a more complex terminal unit is used which permits the subscriber to prepare tape in a local circuit. The tape prepared may also be proofed by running it through the tape transmitter receiving page copy on the page section of the machine. This unit incorporates safeguards permitting an incoming call to take priority over local tape preparation but preventing the destruction of the tape in local preparation by giving warning of an impending call with a 3-second time delay before actual connection of the call. This allows the operator to clear tape under preparation before the incoming call is received. 30
The tape transmission facility with associated tape preparation is particularly attractive in international operation, a feature of Australian traffic, because at the rates charged for international connection the subscriber has a distinct incentive to use maximum line transmission speed and this is obtainable with tape transmission. Two types of line signalling are employed. The simplest of these, which is restricted to cable loops of less than 1,600 ohms resistance, uses single current loop signalling. The second uses two path polar signalling and is used where the subscriber is beyond the resistance limit for single current signalling. Approximately 20 % of terminations are of this type. This type of signalling is also used in country areas where there is no exchange and subscribers are directly connected over a voice frequency telegraph link to a metropolitan exchange. Conclusions The automatic network provided has enabled the efficient handling of Australian telex traffic using a system capable of simple, logical expansion planned for progressive development over many decades. Easy international connection leading shortly to fully automatic operation to a number of countries has been taken into account in this planning in which the Australian Post Office and the Overseas Telecommunications Commission (Australia) have worked in close liaison. Australian interests in this respect have been well served by the work of the International Telephone and Telegraph Consultative Committee which provided the design basis for the system. In particular the signalling system represents contributions from many countries in pursuit of the common desire for effective worldwide communications. The international flavour of communication projects is well illustrated by the Australian telex system. Apart from the design basis previously mentioned, the system uses teleprinters of West German design, terminal units of Australian design, switching equipment of Swedish design, transmission path repeating relays from C. P. Clare, Chicago, to Bell Laboratories design, and semi-automatic positions and switching plant of Australian design using components of United Kingdom, United States and Swedish origin. The relative isolation of Australia from the centres of world communication manufacturing industry has led to a deliberate policy of encouragement of manufacture in Australia, and it is satisfying to note that all of the equipment referred to above, with the exception of the mercury wetted reed relays, was manufactured in Australia. L M Ericsson, through its Australian subsidiary, performed a notable feat in carrying this project to completion with switching equipment manufactured in their Broadmeadows (Melbourne) plant, a plant which was established during the progress of the project. 31
Page 1: 1 1968
Page 4 and 5: Stored Program Controlled Telephone
Page 6 and 7: Signalling in L M Ericsson Telex Sy
Page 8 and 9: On physical subscriber lines other
Page 10 and 11: In a new Recommendation U 11, CCITT
Page 12 and 13: Automatic Tripping of B Subscriber'
Page 14 and 15: egister in ARM selects a new circui
Page 16 and 17: show the signalling both for single
Page 18 and 19: Fig. 11 gnalling for setting up a c
Page 20 and 21: In this case, after receipt of the
Page 22 and 23: Similar intervvorking exists with t
Page 24 and 25: The capital cost of the telex syste
Page 26 and 27: Fig. 1 Traffic distribution by dist
Page 28 and 29: Fig-3 Charging principles Zone char
Page 30 and 31: Transmission Considerations The obj
Page 32 and 33: A variety of special subscriber mar
Page 36 and 37: References 1. C.C.T.T. Illrd Plenar
Page 38 and 39: Corrugating Machine The aim in the
Page 40 and 41: Laying The corrugated duct may have
Page 42 and 43: New Factory Opened at Ostersund L M
Page 44 and 45: Dirivox and Centrum in the Soviet U
Page 46: The Ericsson Group Associated and c

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