Messaging supports out-of-band DTMF using the SIP-INFO method. When there is a mix of telephony vendors in the network, the lowest common denominator, that is, the SIP-INFO method is used for passing DTMFs for all telephony vendors to interwork properly.
Messaging accepts the INFO messages over SIP connections from Avaya Aura® Session Manager or AudioCodes gateway or any telephony server that supports SIP-INFO for DTMF. Messaging interprets the received INFO messages as if these messages had been received in the 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.
There are two INFO formats, and both are accepted by the Messaging system to ensure maximum possible interoperability.
Format Number 1: This is the most popular format. This is an example of the DTMF digit 5 with a duration of 160 milliseconds
INFO sip:7007471000@example.com SIP/2.0 Via: SIP/2.0/UDP alice.uk.example.com:5060 From: <sip:7007471234@alice.uk.example.com>;tag=d3f423d To: <sip:7007471000@example.com>;tag=8942 Call-ID: 312352@myphone CSeq: 5 INFO Content-Length: 24 Content-Type: application/dtmf-relay Signal=5 Duration=160
Format Number 2: This is an example of the DTMF digit 5
INFO sip:7007471000@example.com SIP/2.0 Via: SIP/2.0/UDP alice.uk.example.com:5060 From: <sip:7007471234@alice.uk.example.com>;tag=d3f423d To: <sip:7007471000@example.com>;tag=8942 Call-ID: 312352@myphone CSeq: 5 INFO Content-Length: 1 Content-Type: application/dtmf 5