Signalling system between PBX telephone exchanges - ensures detection of signals by increasing length of first dialling pulse

摘要

The signalling system is used to transmit messages between PBX telephone exchanges. The detection of short dial pulses is made more certain by increasing the length of the first dialling pulse by a predetermined time. This not only ensures that the first pulse is easily detected from amongst all other signalling signals especially when heavy distortion is present but also allows an extra signalling signal to be transmitted with each dialling pulse train. This extra signal transmission can be independent of the actual increase in length of the first dial pulse. The pulse correction circuitry has circuits to increase the length of the first pulse and, at the transmitter, to delay the release of the pulse train.