1.3 Overview

This protocol extends the protocol described in [RFC4733], which describes a mechanism for the transmission of in-band and out-of-band telephony signals.

An in-band telephony signal is where the events or tones are mixed directly into the media stream (typically, audio data). An out-of-band telephony signal is where the events or tones are transmitted through a separate band.

Telephony tones represent the DTMF tones mixed into the audio signal of the media stream. Telephony events represent the different call control events (such as an off-hook event or a specific digit being dialed).

The scope of this protocol is limited to telephony signals using out-of-band transmission. The in-band transmission of digits and tones is not supported by this protocol.