here are my options on the 2n ip verso
The tab below helps you define how DTMF characters shall be received from the intercom. Check the DTMF receiving options and settings of the opponent to make the function work properly.
In-Band (Audio) – enable classic DTMF dual tone receiving in the audio band.
RTP (RFC-2833) – enable DTMF receiving via the RTP according to RFC-2833.
SIP INFO (RFC-2976) – enable DTMF receiving via SIP INFO messages according to RFC-2976.