GB1445800A - Data transmission network - Google Patents

Abstract

1445800 Automatic exchange systems COMPAGNIE INDUSTRIELLE DES TELECOMMUNICATIONS CIT-ALCATEL 26 April 1974 [8 May 1973] 18335/74 Heading H4K In an exchange system in which high bitrate data or speech may be transmitted between subscribers via an exchange CC2 along a twowire line L1, L2 and a call is set up by D.C. signalling, this signalling is carried out by signalling devices, each including two auxiliary wires RON and TRON, which are provided at the subscriber's equipment and the subscriber's exchange line circuit respectively and which enable D.C. to be removed from the line once a call has been set up. Both calling and called subscriber have the RON and TRON wires at their respective equipments and at their respective line circuits, and these latter two pairs of wires are switched through the exchange, along with the two-wire line L1, L2 in the conventional manner. The sequence of operations for setting-up a call, AB2 being the called party, once switchthrough has been completed, is as follows: (a) The calling party, via the signalling device at his equipment, applies a positive potential to the exchange TRON wire which energizes relay I directly, and relay R via the line L1, L2 and transformer circuit T2. Contact r thereby closes to provide a calling signal. (b) The called party acknowledges by depressing key E. Relay PR is energized, resulting in the energization of feed relay A at the line circuit. Thus contact α closes and sends a "connection made" signal to the calling party. (c) The calling party cancels the positive potential at TRON exchange, causing r to open and the calling signal to cease. (d) The called party releases the key E which causes the release of PR and consequently A, thereby removing D.C. from the line.