Solved DTMF not working after Ver.16 upgrade

[gvsoft]

Greetings,

Yesterday I re-installed on a new Windows Server Version 16 because of our provider (cyta) was sold last year to Vodafone, so all SIP equipment is new from our new provider.
After the installation everything was set and working. The difference between the to setups was that instead of using G711 U-law in priority we had to change to G711 A-law because it didn't work.
The thing is that dtmf is not working. We have tried ringing many of our customers (with IVR) and banks and nothing works. I have looked this up and I am seeing a lot of simular problems after going to Ver.16.
What are we supposed to check?

 

[YiannisH_3CX]

Hello @gvsoft

DTMF are usually sent in one of two methods, inband or out of band (rfc2833). Inband DMTF works by sending the different tones via the audio stream and sometimes because of bad audio quality this does not work as tones are not clear enough for the receiving side to decode. Out of band is using RFC2833 which is sending separate messages (events) outside of the audio stream which allows for much better results.

If the provider supports RFC2833 it should declare it in SDP of the Invite or 200 OK message when the call is established. 3CX supports this method by default and all 3CX clients and supported devices are set up to use it. All 3CX supported providers also support this type of DTMF so I would recommend using one of those for better results. https://www.3cx.com/partners/sip-trunks/

The activity log of the PBX should help you see if your provider supports this by checking the SDP of the 200 OK message coming from the provider. You can also use Wireshark if you are familiar with it and check the communication and what is sent by the PBX.

 

[gvsoft]

It was our providers fault for the dtmf.