GB1016273A - Improvements in or relating to telephone signalling systems - Google Patents

Abstract

1,016,273. Automatic exchange systems. STANDARD TELEPHONES & CABLES Ltd. July 5, 1963 [July 10, 1962], No. 26538/62. Heading H4K. In a V.F. signalling system suitable for use over a T.A.S.I. system at least some of the signals include a prefix signalling condition which is maintained until it is acknowledged by the receiver. The invention is described in relation to the tandem connection of a call via two intercontinental links each employing T.A.S.I. systems in which the risk of " freezeout " might result in non-reception of supervisory signals if the latter were all of predetermined duration. Forward transmission.-In the setting up of a call the originating exchange sends a prefix signal P only. Reception at the tandem exchange results in the reversion, a proceed to send signal X. When this is received by the originating register it sends an inter-register signal kp 2 to retain T.A.S.I. association over the link and to cause seizure of a transit register. This signal also indicates that a tandem connection is required. When the transit register is associated it terminates the proceed-to-send signal thereby causing the originating exchange to send sufficient digits to enable the tandem exchange to connect to the second intercontinental link. Intervals between digits are filled by kp 2 signals. When switching is completed a backward proceed to send X signal is sent causing the originating exchange register to transmit a kp 1 signal indicative of the fact that the rest of the digits will be for a terminating call. At the same time the tandem exchange sends forward a prefix signal P and when this is received at the terminating exchange and a register is associated it sends back a proceed to send an X signal which allows the tandem exchange to transmit the kp 1 signal from the originating exchange. When the terminating exchange receives this it associates a terminating register which terminates the backward proceed to send signal which causes the tandem exchange to terminate the backward proceed to send X signal to the originating exchange. The latter then transmits the remaining digits in the same manner as before. Backward answer signal.-The terminating exchange reverts the prefix P which in due course reaches the originating exchange. Also, recognition of this signal at the tandem exchange also causes the latter to maintain this signal, and also causes an acknowledgement signal Y to be reverted to the terminating exchange. This causes the suffix Y to be sent from the terminating exchange to the tandem exchange receipt of this signal terminating the acknowledgement signal. Likewise, when the originating exchange receives the prefix it sends an acknowledgement signal which is maintained until the Y suffix is sent thereto from the tandem exchange.