C5 signalling (CCIT5)
For signaling, a distinction is made between in-band signaling and out-of-band signaling.
C5 is a switching standard for innerband signaling, in which the switching control signals are transmitted over the same lines as the voice information or data.
The C5 control signals are transmitted as tones or tone sequences using the two-tone or multi-tone method. This switching standard is used in the telephone network in Canada, the USA, Australia and China, among other countries.