[asterisk-users] ConfBridge dtmf_passthrough=no doesn't have any effect. Bug?

Joshua Colp jcolp at digium.com
Fri Sep 28 08:56:57 CDT 2012

Markus wrote:

<Snipped long results list>

> PSTN means that I've tested two times, from a regular landline and from
> a mobile. Always calling to the providers DID which ends up in Asterisk
> via SIP. In the case of ConfBridge there were always 2 participants in
> the conference so that I could check if I hear the DTMF on the "other end".

I think your results are sort of skewed. In the case of SIP <-> SIP if a 
local bridge occurs things will optimize and you most likely won't see 
DTMF related messages. They get passed through as packets and not fully 

> "not logged on console" means that I can hear the DTMF tones in
> X-Lite/ConfBridge but Asterisk doesn't seem to recognize them (which is
> fine as not all providers support all DTMF variants).

What log message are you using to determine this?

> My resume is: DTMF is just fine, ConfBridge dtmf_passthrough is not
> working at all. Agree? :)

I've looked at the code for dtmf_passthrough, it's dead simple and 
should be working fine PROVIDED your DTMF is not going through as audio.

My suggestion is to take a step back further.

Just send incoming calls to the Read application and have it store the 
received DTMF in a variable. Next step have it output what was received.

If that works for all cases then Asterisk is recognizing DTMF fine. This 
does *not* mean that the tone will be muted fully as my previous email 

You can further test if all cases check out by sending calls to Record 
and playing back the audio to yourself. If you hear tones and Asterisk 
also recognized the DTMF then it's not fully muted, or the hardware in 
question is sending *both* inband and out of band, which is not supported.


Joshua Colp
Digium, Inc. | Senior Software Developer
445 Jan Davis Drive NW - Huntsville, AL 35806 - USA
Check us out at:  www.digium.com  & www.asterisk.org

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