DTMF tones not acknowledged

I am unable to use DTMF tones via asterisk over a SIP channel from SIP provider.

I have a SIP trunk configured on asterisk with a telasip as a provider. Telasip provides SIP/RTP via asterisk, I am not certain of thier version. I am can make and recieve calls on the channel to and from PSTN with full audio in both directions. I performed a wireshark capture was able to hear dtmf tones being transmitted via the RTP stream.

sip.conf does have dtmf=rfc2833 and telasip has confirmed that they use rfc2833.

I have enabled dtmf -> debug in logger.conf and the logs show no DTMF being recieved.

Thank you for your help.

Does wireshark decode RFC 2833, was the DTMF in band?

I would check the SDP to see if RFC 2833 really is being negotiated and used everywhere needed.

david55 thank you for the reply.

I checked the capture that I was able to hear the dtmf tones on and RFC2833 is present. There were RTPEVENT (apparently these only occure in RFC2833), DTMF codes decode by wireshark. I am able to see the numbers and the “#” however, I am unsure if it is “normal” traffic. For example for a single numeric digit pressed on a cell phone, there appear to be anywhere from 15 to 17 RTPEVENTS with three events for “end.” This occurs each digit pressed on the phone.

I had tried the sip configuration with dtmf relaxed to see if that helped, but it still failed.

It appears if that type of RTPEVENT traffic is “normal.” The following was found at the wireshark wiki

wireshark.org/lists/wireshar … 00011.html

Wireshark-users: Re: [Wireshark-users] Multiple DTMF 2833
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From: Jaap Keuter jaap.keuter@xxxxxxxxx
Date: Tue, 02 Jun 2009 22:43:57 +0200


If you look at RFC 2833 you’ll see it’s a funny protocol.

First of all it pins the RTP timestamp. Then it start to add up time intervals in its payload, for the time the event takes (unknown up front), regularly sending out RTPevent packets to keep the receiver going. Then at the end of the RTP event a repeated ‘end of event’ packet is usual. After that normal RTP flow, with correctly advanced timestamp, resumes. It might even flow in parallel.

As you see a single DTMF key press doesn’t correspond to a single RTPevent packet.


Ujjval Karihaloo wrote:

I see multiple DTMFs in Wireshark (although it was pressed only once), tracing using tcpdump on my asterisk server. Actual packets also are multiple (19 – 20 I believe) with same DTMF tone = 1.

DTMF seems to work OK, but it is difficult to troubleshoot when actual DTMF related problems occur.