Dual-Tone Multi-Frequency Tones

The phone generates dual-tone multi-frequency (DTMF) tones, also called touch tones, in response to user dialing on the dialpad.

These tones are transmitted in the real-time transport protocol (RTP) streams of connected calls.

The phone can encode the DTMF tones using the active voice codec or using RFC 2833-compatible encoding. The coding format decision is based on the capabilities of the remote endpoint. The phone generates RFC 2833 (DTMF only) events but does not regenerate—or otherwise use—DTMF events received from the remote end of the call.