Dual-Tone Multifrequency Signaling (DTMF)

Used for telecommunication signaling over analog telephone lines in the voice-frequency band between telephone handsets and other communications devices and the switching center. The version of DTMF that is used in push-button telephones for tone dialing is known as Touch-Tone. DTMF is standardized by ITU-T Recommendation Q.23. Other multifrequency systems are used for internal signaling within the telephone network.