Post-war and on to 1975 (continued)

From a technology viewpoint, important features included:

• ultimate nation-wide subscriber dialling;


• national closed numbering with a maximum of nine digits;


• grouping of exchanges for call charging;


• extended local service areas;


• automatic multi-metering on trunk calls;


• register controlled, high speed switching system, using automatic alternative routing; maximum of nine links in tandem.

As many of the world's manufacturers of switching equipment were then developing new equipment lines, it was opportune for the APO to choose a new system and have it adapted to its needs. Accordingly a schedule was issued inviting offers and after extensive investigations by a team reporting to F. P. O'Grady, the L. M. Ericsson crossbar system was selected. LME's offer for crossbar included ARF terminal exchanges, ARM 50 series small trunk exchanges, ARM 20 series large trunk exchanges, ARK (M) small terminal exchanges and, apparently added to meet APO particular needs, ARF tandems and ARK minor centres. The switchblocks of all these exchange types had been in use for some time, mainly with DC signalling techniques and in register controlled networks but, although LME was moving to MFC signalling, the details had not yet been finalised. The APO and LME, initially using Swedish resources but later developing considerable expertise in Australia also, collaborated in developing the MFC versions of crossbar and the result was a system which was well matched to Australian needs, with the flexibility to satisfy the requirements of other countries. In the process the system changed extensively.

In order to gain some early experience with crossbar equipment, a contract was let to install an ARF 101 exchange with DC signalling at Toowoomba, Queensland, where interworking problems would be limited.{35{ It was brought into service in 1960, three years before the first ARF 102 exchange with MFC signalling was cutover in May, 1963. The new ARF system was coded ARF102 and although it was developed from the ARF101 type, it was in many respects a new system. The major changes were:

• Provision of an extra wire (UHE 'C' wire) through the group selectors to provide a signal path between FIR and FUR and allow the relay sets to be set to suit the type of connection


• Eliminating the B party ring delay set LKR by adding this facility to FIR and SR relay sets


• Providing much more analysis capability and removing the analysis from the Reg-L to the IGV stage


• Adding a 'waiting place' function to the IGV as a means of reducing post dialling delays


• Adding a decadic sending function to the Reg-L and Reg-I instead of providing a signal conservation register (Reg-U) at the interface with step by step


• Producing a different IGV stage with greater flexibility in availability allocation and more extensive alternative routing facilities


• Increasing the number of backward frequencies from three to five, allowing 10 different signals


• Designing MFC signalling code to allow the extra signals needed with analysis in the GV stage and decadic signalling from the registers Two new SL stage configurations were provided for very high calling rate subscribers and a faster SLK stage marker was developed

Australian Academy of Technological Sciences and Engineering