C7 signalling (CCIT7)

In contrast to C5 signaling, C7 signaling (CCIT7) transmits the data separately from the exchange signals.

In the area between the subscriber and the local exchange, the connection is two- wire; between the exchanges, it is three-wire, via which control codes are transmitted separately from the data.

This signaling concept has the advantage over C5 signaling that the C7 network is more secure because the operator cannot access it directly. Phreaking is not as easy as in the C5 network where the switching signals are transmitted as tones or tone sequences.