eli5: How do DTMF tones produced by another sound source (such as a DTMF smartphone app) dial a number? (on landlines)

87 views
0

eli5: How do DTMF tones produced by another sound source (such as a DTMF smartphone app) dial a number? (on landlines)

In: 2

The electronic in the telephone exchange the landline is connected to is listening for the tones and interpreted it as the number/symbol it represents.

Functionally there are no differences if the tones are generated in the phone or if they are generated by something else and picked up by the microphone on the phone. In both situations, two tones are sent in the wires to the telephone exchange and are interpreted.

An important part is the system is analog only have two wires and control signals like the DTMF tones are on the same wires as sound the microphone the are just mixed together, this is wy you hear the tones. This is called In-band signaling.

For digital systems, the control signal tends to be sent separated from the audio so you can’t control anything by generating sound that the microphone picks up. This is called out-of-band signaling.