Signaling (telecommunications) - In-band Versus Out-of-band Signaling

In-band Versus Out-of-band Signaling

In the public switched telephone network (PSTN), in-band signaling is the exchange of call control information within the same channel that the telephone call itself is using. An example is dual-tone multi-frequency signaling (DTMF), which is used on most telephone lines to customer premises.

Out-of-band signaling is telecommunication signaling on a dedicated channel separate from that used for the telephone call. Out-of-band signaling is used in Signalling System No. 7 (SS7), the standard for signaling among exchanges that have controlled most of the world's phone calls for over twenty years.