In-Band Signalling

In telecommunications, in-band signaling is the sending of metadata and control information in the same band, on the same channel, as used for data.For example, when dialing a modern telephone, the telephone number is encoded and transmitted across the telephone line as Dual-Tone Multi-Frequency (DTMF) tones. The tones "control" the telephone system by instructing the telephone company's equipment where to route the call to. These control tones are sent over the same channel and in the same band (300Hz to 3.4kHz) as the voice and other sounds of the telephone call. In-band signalling is also used on older telephone carrier systems to provide inter-exchange information on how to route calls. Examples of this kind of in-band signalling system are SS5 and R2.
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