Patent GB-555614-A (GB)
Title: Improvements in or relating to telephone or like systems
IPC: H04Q3/00
Filed: 1942-02-27
Abstract: 555,614. Automatic exchange systems. AUTOMATIC TELEPHONE & ELECTRIC CO., Ltd., GILLINGS, C., and MURRAY, L. J. Feb. 27, 1942, No. 2570. [Class 40 (iv)] A 100-line system employs cross-bar switches of the link-circuit type as combined preselectors and final selectors and as group selectors, associated hunting switches being provided for selecting idle outgoing trunks. A cross-bar unit SSU is provided for each set of 10 subscribers' lines, and the 5 pairs of such units each share 4 outgoing and 4 incoming trunks, the former including feed circuits &c. The outgoing trunks from the various units are distributed over 5 switching units LSU, while all the incoming trunks are accessible from the outgoing side of each of these units. Each subscriber unit SSU comprises 10 horizontal bars controlled by relays 1SP ... 10SP, which serve also as line relays, with two additional horizontal bars controlled by relays 0P, 1P to prepare the connection to an outgoing or an incoming trunk, and 4 vertical operating bars controlled by relays ASH ... DSH. Thus each unit is capable of extending 4 connections, and 8 connections can be handled by a pair of units provided not more than 4 are of the same kind, outgoing or incoming. Each switching unit LSU comprises 4 horizontal bars and relays 1CP ... 4CP associated with trunks outgoing from the subscriber units and 5 horizontal bars and relays 1TP ... 5TP for selecting the set of trunks leading to a wanted 20-line subscriber group, connection being made to an idle one by means of 4 vertical operating bars controlled by relays 1CH ... 4CH. When a call is made by subscriber 11, for example, line relay 1SP energizes followed by tens relay 1S, and start relay SA takes into use equipment PCE1 common to 50 subscribers' lines, whereupon a switch HS hunts for an idle one of 4 outgoing trunks marked by 1S and connects up relay OP and the appropriate operating relay ASH, which extends and holds the connection and operates cut-off relay 1K. Relays A, B energize in the feed-bridge circuit and connect up the corresponding horizontal relay 1CP of the switching unit LSU1 to take into use its controlling equipment SCE1. The two dialled digits set marking switches DS, US, the latter being advanced first to a subnormal position if the tens digit is even, whereupon relay SGA operates to seize common equipment FSC which hunts for the equipment SCE1 and supervises the completion of the connection. The set of 4 trunks leading to the wanted 20- line group are marked over DS4, 5, and a switch TS now hunts for an idle one as indicated by the condition of the corresponding internal links of the unit LSU1 and of the pair of subscriber units serving the 20-line group. Relay KR responds and connects up the appropriate operating relay CH, a relay TP being already operative in accordance with the tens digit. Relay 1CS energizes and makes a circuit over DS7 for relay 1P of the wanted subscriber unit, and during the operating period of relay G the wanted line is tested over DS8 and US3 or 7, an idle condition being indicated by battery on wire T over relay SP. Relay SK responds to this condition and applies direct ground to energize SP and also connects up the appropriate operating relay ASH over DS6 and TS7 or 8. The equipment FSC is released, and the operation of relay SD in the feed-bridge circuit dissociates the controlling equipment SCE1 and initiates ringing, the connection being completed upon reply. If the wanted line is busy, or if the switch TS fails to find an idle trunk, the operation of relay G gives a busy signal. Failure to dial results in the operation of SD, SE which dissociate the equipment SCE1 and give NU tone. It should be noted that relay 1CS of the equipment FSC is interconnected with the start relays SA of the equipment PCE1 and similar equipment PCE2 (not shown) so that the extension of a calling line and the testing of a wanted line cannot take place simultaneously.