This may constitute an information exchange concerning the establishment and control of a telecommunication circuit and the management of the network.
In the public switched telephone network (PSTN), in-band signaling is the exchange of call control information within the same physical channel, or within the same frequency band, that the message (the callers' voice) is using.
An example is dual-tone multi-frequency signaling (DTMF), which is used on most telephone lines to customer premises.
[1][2] In the mid-20th century, supervision signals on long-distance trunks in North America were primarily in-band, for example at 2600 Hz, necessitating a notch filter to prevent interference.
A signaling protocol is a type of communications protocol for encapsulating the signaling between communication endpoints and switching systems to establish or terminate a connection and to identify the state of connection.