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Common DTMF Issues

Posted February 17th, 2008 by ja133

Please edit this page if necessary.

Many posts lately have been about DTMF (sip and iax) not working properly, either with incoming or outgoing call.

Those who have trixbox and asterisk up to date (trixbox 2.2.12/asterisk 1.2.26 or later, or trixbox 2.4.2/asterisk 1.4.18 or later) should not be expecting DTMF issues. However, if DTMF issues are found, you may try one of the following. If your DTMF issues are still unresolved, you may need to contact your voip provider.

Outbound DTMF- not all DTMF digits are being processed to the other caller:
- Latency issues may be causing this. Ping your voip's sip server, and normally you should not be expecting issues when the response time is under 45ms. If your provider blocks ping requests, run a traceroute and make sure that there is not too much latency between you and the carrier.
- Often, DTMF issues may also be caused because your server is located in New York (for example) and the remote server is all the way in Missouri. If this is your case, read more below, and if it still doesn't resolve your issue, try looking for a provider closer to your hometown.
- In your trunk settings, under PEER Details, you would normally see a line containing dtmfmode=(whatever). Usually it would be set to rfc2833. Sometimes you will not have this line. Either way, add or replace the line with: dtmfmode=inband and then see if both outgoing DTMF and DTMF pressed by the caller (during an outgoing call) is reliable. If it is not reliable, try dtmfmode=auto
- Currently there is a known problem with Voice Pulse Connect's outgoing DTMF when using the servers connect01, 02, 03.voicepulse.com. Switch over to their new servers, nyc or sfo.voicepulse.com (you will need to download the newest module).

DTMF on incoming calls are not processing through your IVR:
- When testing this, ALWAYS test using a non asterisk box, and at the end, make sure it works on both a non asterisk box and an asterisk box (where the phone call runs over sip/iax and not POTS or PRI lines).
- Add or replace the line in the trunk settings: dtmfmode=rfc2833
- If that didn't work, try dtmfmode=inband or dtmfmode=auto
- If none of these worked out for you, you will need to contact your service provider to troubleshoot with them. Often they would need to manually force the DTMF mode to inband on their end.