DTMF stands for dual-tone multi-frequency. DTMF is a signaling system that recognizes the keys or numbers dialed on a telephone keypad. The first telephone systems used pulse dialing signaling. Later, the system was updated to multi-frequency (MF) dialing.
DTMF is a multi-frequency tone dialing system used by the keypads in landline and mobile phones to deliver the number or key dialed by the caller. DTMF has allowed long-distance signaling of called numbers in voice frequency ranges over telephone lines. This has removed the need for telecom operators to switch between a person calling and the person receiving a call
At Plivo we support only out-of-band DTMF.
The incoming stream delivers DTMF signals out-of-audio using the RFC-2833 mechanism, independently of codecs. In other words, the DTMF signals are sent separately from the actual audio stream.