Patent GB-317879-A (GB)
Title: Improvements in or relating to automatic and semi-automatic telephone systems
IPC: H04Q3/58
Filed: 1928-05-24
Abstract: 317,879. Standard Telephones & Cables, Ltd., Wright, E. P. G., Baker, J. H. E., and Cameron, A. H. May 24, 1928. Automatic exchange systems. - A selectorrepeater in a satellite operates initially to select a main office junction and extends calls locally when necessary under the control of a discriminating device which is associated in multiple with a number of selector-repeaters. In the first of the two systems described, discrimination is effected by one digit. The selector repeater comprises two switches, one of which hunts for the junction. The other, which has two sets of wipers, hunts for a local line in one or other of its banks according to the value of the 1st digit. In the other system, which is arranged for twodigit discrimination, the selector-repeater has only one switch which gives access to junctions over the 1st part of its bank and to a number of groups of local trunks over the remainder The local group over which the call is to go is marked by the discriminating switch in accordance with the 3rd digit. Single-digit discriminator, Fig. 1. When the selector repeater is seized, K, BB pull up over the test wire. K seizes the discriminator and BB removes a shunt from itself to mark the associated selectors busy. Line relay A energizes release relay B which makes driving and test circuits for the switch JS. When an idle junction is found, HJ pulls up in series with its relay JT and switches through. The junction is thus bridged by relays D, I which are temporarily shunted by a resistance which is cut out when I pulls up. This arrangement ensures quick operation of the distant line relay and prevents it from being interfered with by the re-insertion of the inductive bridge after each digit. JT marks the junction busy by removing a shunt from itself and disconnects JB which is provided for marking the junction busy by cutting off JT when the common apparatus at the incoming end is in use. The first digit is repeated by relay A over the junction and to the discriminator SC. If the call is local (digit 6 or 7) series relay CC at the end of the digit makes driving and test circuits over SC2, SC3 for the double wipe.r switch LS which hunts under control of HLA or HLB in one or other of its banks (depending on the digit) for a local selector. The operation of HLA or HLB releases K, BB to free the common apparatus and HJ to free the junction, and sends JS to its last terminals. If the call is not local, DD is energized and releases K, BB. Busy signal and statistical metering. If all junctions are busy JS stops on its last terminals and GG pulls up in series with HJ, which however does not pull up to send back the busy tone connected to the last terminals unless it is determined that the call is for the main office, when a new circuit is made for it by DD which also locks up GG pending the relapse of BB and completes a circuit over SC4 for operating the appropriate traffic meter. If the local selector is unsuccessful, HLA or HLB pulls up over the last terminals in series with H, locks up and sends the busy signal end energizes II which locks up pending, the relapse of BB and operates the appropriate traffic meter. Release. On the relapse of A, B, the switching relay falls and the switches go home. C is operated during their homing and holds the test circuits open. Two-digit discriminator, Fig. 2. When the selector is seized, the switch S hunts for a junction under control of H. Relay A repeats the digits over the junction and to the common switch SC. If the call is local (digits 5, 8), CC at the end of the first digit energizes GG which locks over the off-normal arc, homes the switch, and partially energizes EE which pulls up completely when GG falls back and alters the marking on bank SC3 so that a similar restoration takes place in response to a 2nd digit 8, GG this time causing two-step operation of DD which releases H. The selector then proceeds to the terminal X where it is stopped by HH. The third digit also goes to SC and as soon as the, latter moves off-normal, HH falls and the selector moves off again. If it catches up the switch SC it is stopped by HH. After the relapse of CC at the end of the digit however the selector is driven independently of HH and the energization of HH when the selector reaches the wanted group gives control to the test relay H. When an idle selector is found, H short circuits K, and K, BB fall back and free the control switch. As soon as it is decided that a call is not local, the relapse of CC energizes FF which, provided a junction has been selected, short circuits K to free the control circuit. Busy signal and statistical metering. If all junctions are busy, the selector is stopped by HH on the terminal X, and if FF pulls up to indicate that the call is an external one, II is connected to the test terminal, to energize H which locks up, energizing II, sends back the busy signal, and short circuits K to free the common apparatus. II locks up pending the relapse of BB and operates the junction traffic meter. If all local trunks are busy, the selector goes to its final terminals. HH which falls back when the wanted group is left, pulls up again to stop the switch on its last terminals, and H pulls up in series with II, and sends the busy tone, II connecting up a local traffic meter.