In-Band Signaling is any signaling transmission that takes place within a range of frequencies that are normally used only for data transmission (voice and video). When dialing from a land-line telephone, the telephone number is encoded and transmitted across the telephone line in form of dual-tone multi-frequency signaling (DTMF). The tones control the telephone system by instructing the telephone switch where to route the call. These control tones are sent over the same channel (copper wire) as the audio of the telephone call.
In-band signaling is also used on older telephone carrier systems to provide inter-exchange information for routing calls. Examples of this kind of in-band signaling system are the Signaling System No. 5 (SS5) and R2 signalling.