[asterisk-users] DTMF inband with telephone-event in SDP

[Jakob Hirsch]

Hello everyone!

We use Asterisk for various services like voicemail. Our SIP clients
usually use rtp events (rfc2833) for DTMF, which works just fine and
independent from the codec (g711 vs. g726 etc.).

Now we noticed there are some SIP clients that announce telephone-event
in their SDP, but send their DTMF inband. The problem with that is, that
Asterisk obviously does not try to detect inband DTMF after seeing the
telephone-event payload type in the SDP.

So we are in a kind of dilemma:
- dtmfmode=auto (and dtmfmode=rfc2833) will work for most, but not for
the described ones.
- dtmfmode=inband would also work for most, but of course not for the
ones using g726 et al.

Is there any Asterisk setting to force inband DTMF detection (with
non-compressing codecs only, of course)? I browsed the code without result.

Does anybody have a hint how to handle this? Or if the SIP clients
behaviour is even RFC compliant?


Regards and TIA,
Jakob