Unreliable DTMF on outbound calls

DTMF on outbound calls from our SIP phones is unreliable. The problem appears to be specific to certain external numbers, and the symptoms are that after the call connects key-presses on the phone don’t generate any audible tone and are not recognized by the remote application (e.g., an IVR). We have not experienced any other problems with outbound calls.

We are running Trixbox 2.2/Asterisk 1.2.18 with zaptel 1.2.19. The PBX has a TDM400 card which we use for a small number of internal analog phones – none of which exhibit this behavior when calling outbound – and a TE120 which we use for our fractional PRI connection to the external world.

Our SIP phones are a mix of Aastra 9112i’s and 9133i’s, as well as the X-lite client. I have tried increasing “toneduration” in zapata.conf. I have also tried setting “dtmfmode” to “inband” in extensions_additional.conf (via the FreePBX GUI) and disabling out-of-band DTMF on the Aastra phones. None of these measures fixed the problem.

Any ideas? Again, outbound DTMF from the SIP phones generally works, but there are some external numbers for which it does not.


DTMF in 1.2.X is severely broken. Try applying this patch: h6315.com/dtmf.patch

Dovid, thanks! I am traveling at the moment but will try this in a week when I’m again able to lay hands on the PBX.

Has this patch been integrated with the 1.2 tree (e.g., 1.2.24)? If so, I may upgrade our entire asterisk installation.

I do not believe so. It was given to me by a carrier that I was testing with. After applying that patch it worked great with numerous carriers.

Is that patch incrementing the duration of the DTMF start events?

I am unsure what it does other than that it fixed the issue for me.

I have not has success with dtmf with both voice pulse and vitelity (only 2 providers i ever tested it on) with asterisk 1.4 and 1.2
maybe ill try this patch
How do i apply this patch though?

Problem is when you call to specific outbound numbers from your SIP phones or when you call using specific outbound numbers/lines?

anyway, try ‘relaxdtmf=yes’ and ‘toneduration= more than 100’ in zapata.conf

also play with ‘dtmfcodec=101’, ‘dtmfmode=inband or rfc2833’, ‘relaxdtmf=yes’ in zapata.conf and sip.conf

also note this:

[quote];rfc2833compensate=yes ; Compensate for pre-1.4 DTMF transmission from another Asterisk machine.
; You must have this turned on or DTMF reception will work improperly.[/quote]

Thank you. I’ll try it. I’m also using trixbox 2.2 but I will add it to the trunk settings on both systems. The one using asterisk 1.2 and the one using 1.4
This happens on outbound calls only

using asterisk 1.4 i set on the trunk AND in sip.conf the following:


still not working though
outbound calls are still not passing all DTMF tones
any other way i can fix it?

I had the same problem when i first installed asterisknow, the solution for this case is to change the DTMF to “inband”, this problem occured only with the latest version of asterisknow because older version worked properly.

I have this done, but it must be set manually on each extension. If i leave the extensionnss on rfc2833, it wouldn’t do any good even if i set inband on the trunk. Only problem with having this set up per extension is that when people want to record their greetings for voicemail, when they hit # to end recording, the person hearing this recording hears the # tone too. My trunk runs through vitelity.
On g729 and GSM I don’t have this issue when dtmf=inband though

That is exactly what i mean, change for each extension.
have a nice time