[asterisk-users] Inband DTMF not detected - bug or config error?

[Sebastian Damm]

Hi,

we have an Asterisk server basically passing on calls using the Dial
application. In the pjsip endpoint settings, the dtmf_mode is set to audio.
This works with most calls. However, there is a scenario where DTMF tones
don't get forwarded the way I would expect them to get forwarded.

A: Caller without RfC4733 support
B: our Asterisk, version 17.6.0
C: Another Asterisk, with RfC4733 support, running an IVR

Now when the call comes in, our Asterisk (B) sends out a new call, offering
telephone-event to C. However, since A and C use the same codec, B bridges
those two calls using a native bridge. And that's probably the reason why
it doesn't detect inband DTMF tones from A, but instead just passes on the
media stream to C. C, however, thinks DTMF should come as RTP events, not
detecting the tones coming inband, either.

The documentation says, the native bridge is not capable of doing anything
with DTMF, but the core bridge would be. (
https://wiki.asterisk.org/wiki/display/AST/Bridges)

In my opinion, Asterisk should not enter native bridge, when dtmf modes for
the two channels differ. Is this a bug? If it isn't, is there a way to
force Asterisk to use the core bridge, so DTMF tones get detected inband
and converted to rtp events?

Any hint appreciated.

Regards,
Sebastian
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