Try something like this:

  <extension name="inband-dtmf" continue="true">
    <condition field="${switch_r_sdp}" expression="a=rtpmap:\d+
telephone-event\/\d+">
      <action application="start_dtmf"/>
    </condition>
  </extension>

I think the wiki used to have an example, but I don't see it on confluence.

On Sat, 13 Oct 2018 at 00:15, Michael Jerris <mike@jerris.com> wrote:
There are vars with the full SDP, you can do a regex condition.  Check the info app to see all the vars you have at your disposal.  There may be a var for the te as well to show the pt.

Mike

On Oct 10, 2018, at 6:53 PM, Andrew Keil <andrew.keil@visytel.com> wrote:

To FreeSWITCH Users,
 
I have just noticed when making calls internationally to the UK from Australia that the following SDP sometimes happens when the call lands on FreeSWITCH:
 
d5f14e47-2156-4236-be16-4eef1b7e9d3d 2018-10-04 06:59:28.819816 [DEBUG] sofia.c:7301 Remote SDP:
d5f14e47-2156-4236-be16-4eef1b7e9d3d v=0
d5f14e47-2156-4236-be16-4eef1b7e9d3d o=sbc-uk-mr-dh05a 451499 139728 IN IP4 XXX.XXX.XXX.XXX
d5f14e47-2156-4236-be16-4eef1b7e9d3d s=sip call
d5f14e47-2156-4236-be16-4eef1b7e9d3d c=IN IP4 XXX.XXX.XXX.XXX
d5f14e47-2156-4236-be16-4eef1b7e9d3d t=0 0
d5f14e47-2156-4236-be16-4eef1b7e9d3d m=audio 62754 RTP/AVP 8
d5f14e47-2156-4236-be16-4eef1b7e9d3d a=rtpmap:8 PCMA/8000
d5f14e47-2156-4236-be16-4eef1b7e9d3d a=ptime:20
 
This then creates the following message around call answer: 
 
d5f14e47-2156-4236-be16-4eef1b7e9d3d 2018-10-04 06:59:28.839799 [DEBUG] switch_core_media.c:5766 No 2833 in SDP. Liberal DTMF mode adding 101 as telephone-event.
 
From this point on DTMF is NOT detected by the FreeSWITCH IVR service.  I assume I would then need to use mod_dptools: start_dtmf to detect the DTMF tones within the channel.  Which I am yet to test.
 
However my main question is whether there is a channel variable that would enable me to check whether 2833 support is not inside the SDP?
 
Regards,
 
Andrew Keil 
 

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