[Freeswitch-users] DTMF recognition flaky

Jason White jason at jasonjgw.net
Thu May 7 03:16:32 PDT 2009

Remko Kloosterman <R.Kloosterman at mtel.nl> wrote:
> Did you make a wireshark trace yet? You should be able to find out
> exactly what's going on there, which protocol is used, etc. We've had
> our share of problems with DTMF over SIP trunks as well. 

I've just discovered that I'm having a similar problem to the one discussed in
this thread. Here are the symptoms.

1. If I call FreeSWITCH from my Snom 320 SIP phone, DTMF recognition works
perfectly. This is also true if I call a friend's FreeSWITCH system.

2. If I call a certain VoIP provider from the Snom phone, via FreeSWITCH
(phone -> FreeSWITCH -> provider) and call the provider's DTMF test, DTMF
recognition fails to work. Apparently this provider accepts only RFC-2833,
which is what FreeSWITCH should be issuing - I haven't changed the settings in
the external profile from the defaults.

3. If I call the same provider's DTMF test from PortAudio and issue the pa
dtmf command, the provider recognizes the DTMF traffic correctly.

I couldn't find any obvious configuration errors on the phone or in my
internal and external Sofia profiles.

I'll gladly run tshark if that's the next step to take.

I can also try setting <param name="pass-rfc2833" value="true"/> in the
internal profile, but this shouldn't be necessary, since as the wiki states in
documenting this variable, FreeSWITCH should decode and re-encode the RFC2833
data anyway when this is set to false.

I'll keep working on this, but in the meantime, suggestions are welcome.

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