Created by Ryan Harris, last modified by Attila Gulyas on 2020.10.19
A, B, C, D tones
Make sure to expect (and handle) the DTMF tones
C , and
D; these are very rare nowadays but they are still possible to send (e.g., someone has an old device with the extra ABCD column). See DTMF for more.
string For inband DTMF, start_dtmf must be used in the dialplan.
<action application="set" data="dtmf_type=info"/>
<action application="set" data="dtmf_type=rfc2833"/>
TODO RFC 2833 is obsoleted by RFC 4733.
<action application="set" data="dtmf_type=none"/>