Post-war and on to 1975 (continued)

The international signalling system employed was the CCITT Interim Telephone Signalling System No. 5, which had previously come into use in the Atlantic but had not been applied before over such long international circuits as existed between Sydney, North America and the United Kingdom and the use of echo suppressors to control echo on the long international cable circuits was also a new development for Australia. Much of the assembly and wiring of relay sets of the 5005 exchange was undertaken by TEI at their Meadowbank works near Sydney, the work in general being related to the special application of CCITT No. 5 signalling, national loop-disconnect register signalling and special code conversion requirements.

The major changes which the Australian network was undergoing as crossbar switching and seven digit numbering were being introduced, made it desirable to insulate the international network from the frequent changes occurring in the APO network, to provide for international practices which were not possible in that network and to enable the APO to initiate calls from gateways in distant capital cities. The international exchange was, therefore, equipped to perform some unusual, perhaps unique, functions. The principal ones were:

1. For calls incoming to Australia, a 'number converter' was provided, so that overseas telephonists need dial only an Australian subscriber's ultimate number in the Australian numbering scheme.


2. For calls outgoing, a special dummy digit in the dialling train triggered the generation of international function signals which did not exist in the Australian network.

With the COMPAC cable bringing reliable, high quality communications to Australia from Europe and North America, there was a requirement to provide similar communications from Australia to South East Asia and to enable circuits in COMPAC to be extended to this region. To achieve this a Commonwealth Cable Conference was held in Kuala Lumpur in 1961 to plan such an installation and laying of the SEACOM cable began in 1964 and was completed in 1967, with the Australian terminal at Cairns, North Queensland. The Singapore-Kota Kinabalu-Hong Kong-Guam sections had the same capacity as COMPAC, but this was doubled to 160 3kHz channels for the Guam-Madang-Cairns sections. At Guam a land interconnection was arranged with the Hawaii-Japan cable system. The APO was responsible for linking the Cairns terminal to Sydney by microwave and this required special attention to design in order to obtain low noise performance needed to match the standards imposed by CCITT for international systems.

With the advent of the COMPAC and SEACOM submarine telephone cable systems in the early nineteen sixties, a Commonwealth Cable Management Committee was formed to, amongst other things, oversight the optimum use of the cables' capacity. OTC, as one of the owners and users of these submarine cables systems, recognised at an early stage the usefulness of computer techniques in network planning and in the mid nineteen sixties developed and operated a network dimensioning and analysis tool, using information on traffic volumes and network configuration to determine circuit quantities, to provide the INTELNET programme which was then operated by OTC on behalf of the Partnership for several years. It used analytic techniques, with state-of-the-art modelling of traffic behaviour in automatic alternate routing hierarchical networks, as well as catering for variations in traffic flow throughout the 24 hours of the day. At the time of its development, the programme, together with the use to which it was put, was unique. The two principal benefits accruing to the Commonwealth partnership were firstly, highly efficient exploitation of the expensive capacity available in intercontinental transmission systems by use of alternate routing and secondly, exploitation of the time difference between various countries around the world, whereby circuit utilisation efficiency could be further increased by concentration of traffic streams of different busy periods.

Australian Academy of Technological Sciences and Engineering