Patent GB-441644-A (GB)
Title: Improvements in or relating to automatic telephone systems
IPC: H04Q3/00
Filed: 1934-10-13
Abstract: 441,644. Automatic exchange systems. GENERAL ELECTRIC CO., Ltd., Magnet House, Kingsway, London, and MOSS, B. F., c /o General Electric Co., Ltd., Stoke, Coventry. Oct. 13, 1934, No. 29338. [Class 40 (iv)] In a system comprising a number of exchanges in a chain with a number of junctions between each exchange and the next, switching apparatus is provided at each exchange whereby on an outgoing call from any exchange, an attempt is made to establish a through connection to all exchanges. In the system described, two junctions extend from each exchange to the next and at each exchange, two link circuits with associated relay groups each have access to the two or four junctions at the terminal or intermediate exchanges respectively. Considering a call outgoing from an intermediate exchange, a selector in response to a significant digit seizes one of the link circuits, the switching relays of which connect up one or other of the junctions in each direction with a result that battery is fed over the junctions which causes one or other of the link circuits at the adjacent exchanges to extend the connection through these exchanges. These operations proceed until the terminal exchanges are reached or until a junction's busy condition is encountered. The next digit significant of the wanted exchange is received by switches individual to the link circuits at all the exchanges which have been connected up, and the switches determine the junctions which are to be maintained in use, the remainder being released. Further exchanges may be branched off the chain but these would require extra digits. More than two relay groups and more than two junctions with increased number of relays per group may be provided. Connection to junctions at originating exchange. It will be assumed that the exchange is an intermediate one, operations at a terminal exchange being similar except that junctions extend therefrom in one direction only. A selector (not shown), in response to a digit signifying an inter-exchange call, seizes trunk 5 whereupon A, AB, CA, MA, MB operate. Relay AB opens the circuits for operating the switching relays CA .. CD on incoming calls, and MA, MB respectively make circuits for the pairs CA, CB and CC, CD which select junctions to the two adjacent exchanges. One of each pair operates more quickly and disables the other and it will be assumed that junctions 1 and 3 are taken into use, battery being fed to these junctions over coil RC. A second link circuit and relay switching group DA..DD indicated by dotted connections are provided for use if the first group is busy. Connections at incoming exchanges. Assuming an exchange reached over junction 1 and applying the Figs. to the incoming exchange, the call comes in over junction 3 and battery fed from the calling exchange operates CX which makes circuits for switching relay CC and the corresponding relay DC of the second group, the operating times of the relays of the two groups being different. If the first group is busy, the circuit of CC is open at contacts of AB. Assuming CC operates, junction 3 is switched through, DC is disabled, and AA in the local loop pulls up to energize AB, CR, MA. It will be seen that MB does not operate in this case so that CD cannot be operated to connect up junction 4, but MA operates either CA or CB to switch the connection through to the next exchange. The complete chain is built up in a similar manner. Release of unwanted junctions and completion of connections. The next digit, significant of the wanted exchange is repeated by A to switch K at the originating exchange and by reversals of battery feed over RC to polarized relays AA at each exchange which repeat the impulses to the switches K at these exchanges. Relay C at each exchange falls back at the end of the digit and releases CR, which has been held over bank K2, to prevent further digits going to K, and to connect the speech path at the originating exchange. Bank K3 has all contacts grounded corresponding to exchanges in one direction, K4 has contacts corresponding to the other direction grounded, whereas K5 has its own significant contact grounded. At the originating exchange, the relapse of C short-circuits one or other of relays MA, MB depending on the direction of the wanted exchange, so that one of the switching relays CA, CC falls back releasing the AA relays and junctions in the unwanted direction. At exchanges lying between the originating and wanted exchanges, the relapse of C does not short-circuit the operated relay MA or MB as the case may be since B is not operated at exchanges other than the originating one. At the wanted exchange, the relay MA or MB which had been operated to extend the connection beyond that exchange, is short-circuited over MH and the ground on K5 so that the corresponding switching relay falls back. The relapse of MA or MB also completes the loop to the local trunk 5 and further digits are repeated by AA to the local switches. Release. When the calling party replaces his receiver, the relapse of A at the originating exchange is followed by that of the AA relays at the other exchanges involved in the connection, the AB relays relapse and the switches K go home. At the called exchange the relapse of AA releases the local switches. Busy signalling. The only busy condition immediately signalled is an all relay groups busy condition at the originating exchange which is performed by the selector in any known manner. If a complete chain cannot be connected up, the busy condition is not signalled until the exchange digit has been sent since the busy portion may not be required. For example, an incoming call on junction 2 operates BX and BY pulls up to connect busy tone if the connection is not switched through due to a relay groups busy condition. This is however not heard at the calling exchange until CR relapses at the end of the transmission of the exchange digit. If all junctions are busy, the operation of MA or MB cannot energize either of the corresponding pair of switching relays so that on the relapse of CR relay BS pulls up over a rectifier to connect busy tone.