Messaging supports out-of-band Dual Tone Multi-Frequency (DTMF) using the SIP-INFO method. Out-of-band DTMF transmits DTMF tones separately from the voice channel. When there is a mix of telephony vendors in the network, the SIP-INFO method, the lowest common denominator, is used for passing DTMFs for all telephony vendors to interwork properly.
Messaging accepts the INFO messages over SIP connections from Session Manager or AudioCodes gateway or any telephony server that supports SIP-INFO for DTMF. Messaging interprets the received INFO messages as if they had been received in the Real-Time Transport Protocol (RTP) stream using standard RFC 2833 DTMF signals. Session Manager, or AudioCodes gateway, or telephony server then routes the SIP-INFO messages along with the rest of the SIP signaling messages to the dialog to which the SIP-INFO messages belong.
Messaging accepts all incoming SIP-INFO messages and interpret the messages as if they had been received in the RTP stream as RFC 2833 compliant digits. Messaging can also ignore all SIP-INFO DTMF digits in the signaling stream. Messaging, by default, ignores the SIP-INFO DTMF digits in the signaling stream to avoid double detection of DTMF digits, in case the far end sends DTMF digits on both the signaling and the RTP channels.