IMPROVEMENTS IN OR RELATING TO AUTOMATIC TELEPHONE SYSTEMS

1,206,781. Automatic exchange systems. AUTOMATIC TELEPHONE & ELECTRIC CO. Ltd., and POST OFFICE. 7 March, 1968 [30 May, 1967], No. 24831/67. Heading H4K. Loop disconnect impulse digit signalling from a path set up over Strowger switches is received by register access circuits RAC of which one is provided in each of the forward paths into a cross-bar group selector, a group of registers REG fewer in number than the number of access circuits being connectible to incoming paths IP to store a digit received in loop disconnect form and having done so to obtain the use of a common high speed sender DCS which forwards the digit to a stage register in the crossbar group selector when this reverts a proceedto-send signal. The sender DCS may transmit with coded D.C. leg signals or may be such as to transmit frequency combinations. The system is that described in Specification 1,131,367 but differs in that digit code converters are not provided in all access circuits to the cross-bar group selector. As shown in Fig. 1 eight groups of twelve speech paths IP1 to IP96 each contain a register access circuit RAC and give access to corresponding access circuits AC1 to AC96 of eight twelve inlet cross-bar switches. A group of one digit registers REG1 to REG16 is available to the access circuits RAC each one of which is served by a set of five of the registers the sets of five being distributed to equalize register use. A loop disconnect impulse detected in a register access circuit RAC produces an application to a call isolator CI comprised of a one-out-of-eight and a one-out-of-twelve lock out chain such as to select only one out of competing demands for the isolator. The selected, or the only, calling access circuit RAC is singled out by the isolator CI by connecting energizing battery to one side of a set of five register connect relays in that access circuit. A register interrogator/selector is instructed by isolator CI to examine the group of five registers available to the access circuit and, in accordance with a cyclic order of choice to equalize use, allots a free register REG. When seized the register extends earth across all the access circuits RAC for which it provides service and in this way operates the register connect relay corresponding to itself in the access circuit singled out by battery from the isolator CI. A four wire path now connects the register to the access circuit RAC, two wires connecting the incoming loop for the detection of loop disconnection