GB1380480A - Telecommunication systems - Google Patents

Abstract

1380480 Automatic exchange systems STANDARD TELEPHONES & CABLES Ltd 22 Dec 1972 59386/72 Heading H4K In a telecommunication exchange which is dependent for part of its operation on a parent exchange, communications within the exchange and to the parent exchange are effected in T.D.M. manner, subscriber lines are scanned repetitively for loop state signals, detected changes of state as compared with stored representations of the loop states during the preceding scan are used to compile digits in a register seized when an initial off-hook condition is detected, a wanted number or part thereof is compared with the directory numbers of subscribers connected to the dependent exchange and in the case of a local to local subscriber call a match is detected and the connection is set up independently of the parent exchange, the numbers being stored in the equipment/ directory number translator. As shown signals from subscriber lines and trunks of the parent exchange are received at the left hand side of the figure at receive terminating units RX TERM and are selectively gated via a highway H1 or H2 and corresponding demultiplexer DEMUY 1 or DEMUX 2 to subscriber lines or outgoing trunks. For a bidirectional connection two separate paths must be set up. The lines, trunks and highways may employ delta sigma, P.C.M. or pulse amplitude T.D.M. transmission. The exchange control includes an equipment number counter and addressed synchronously therewith connection stores CS1 and CS2, channel state and connection state code stores giving the calling state of the subscriber associated with a currently scanned equipment number and the current state reached in that connection, and a translator giving the directory number and class of service of that subscriber. This subscriber is the called subscriber in that the transmit terminating units TX TERM are enabled cyclically and the addresses read out of the connection stores CS1 and CS2 identify the called subscriber gates to be enabled. The line scanner(s) and dialled digit receivers are connected on the called subscriber side and operate only during their allotted time slots. The call state stores during ringing &c., override the normal control of the connection stores address decoders D1 and D2 to cause them to open alternative crosspoints to gate appropriate tones to the subscribers. In the case of call to or from the parent exchange the identity of the trunk used may be transmitted with the directory number of the wanted subscriber. A separate signalling channel between the exchanges is employed.