Post-war and on to 1975 (continued)

By late 1963 the completed designs comprised ARF terminal exchanges for metropolitan networks and ARK-D for country exchanges up to about 1400 lines. Larger country exchanges could use the metropolitan ARF and, although a less elaborate design for country areas was intended, it was not an urgent need. Design priority was then given to ARM, and particularly to those parts of it required to establish full STD from the capital cities.[36] The APO had earlier expressed interest in a three-stage group selector to give greater availability and the necessary development work was undertaken locally, with major contributions from N. M. H. Smith. Originally, it was intended to use ARM for all trunk switching centres except for a few small minor centres for which an ARK523 design had been offered. As the ARM design proceeded, the first-in cost rose substantially and alternatives were sought for small minor centres, including investigation of the ARK523, but its limited traffic capacity was found to make it unsuitable. Attention was then directed to the possibility of using ARF as a minor centre, relying on an ARM secondary centre to undertake the more complex tasks.

The ARF minor centre role and design evolved over a period from initial ideas based on minimum facilities to a complete minor centre.[37] Initially, terminals were to be ARK-D with multi-metering provided at the parent secondary centre, except for a few fixed rate routes, and with trunk traffic within the minor area 'trombined' via the secondary, an arrangement which would have involved little new design work, and in fact most early ARF exchanges in the country were trunked in this manner, except that instead of a route to a secondary centre, there was a route to a manual trunk exchange. New possibilities, however, arose from the development by LME of a modular register architecture intended to simplify the provision of special features in registers, reducing the register to little more than a digit store with access to peripherals which were called in as needed to provide signalling and analysis functions. The proposed provincial register, REG-LP, was developed on this basis, with control of ARK-M exchanges provided by an add-on unit to become REG-ELP. Two further additions were made to the ARF minor centre, the most important being REG-H4, which provided local charging facilities, initially as a means of avoiding the tromboning of intra minor traffic, but developed to charge all traffic at the minor centre. The second was a terminating register, REG-YILP, to allow direct routing by-passing the terminating ARM.

The development of an ARF minor centre changed the nature of the ARM exchanges also and the REG-E function of controlling ARK-M was never implemented and most ARMs did not have to provide charging. The functions left the ARM were four wire transit switching, terminating analysis, control of echo suppressors and providing the switching for AFG manual trunk assistance positions. Although the new register provided an economical design for average size minor centres, there was a need for a design suited to small centres serving between 500 and 2000 lines, but its economic justification was eroded by reduced transmission costs and the project was deferred.

Australian Academy of Technological Sciences and Engineering