Signalling system between main and PBX telephone exchanges - prevents loss of secondary signalling signal information by repeating it

摘要

The signalling system, for signalling between a main telephone exchange and a PBX ensures that secondary signalling signals are easy to transmit whilst guaranteeing that signals have through-access in certain directions. 50 Hz ac is used for main signalling and AF multiple-freq. signals for secondary signalling. The secondary signalling signal (denoting type of connection and/or authorisation) that follows the main signalling immediately after a subsequent second main signalling signal which is the same as the first has been transmitted. This ensures that no information is lost if the first secondary signal is distorted.