DTMF Issue - RTP RF2833

[arillera]

Hello,

We are having an issue where when our staff is using the WebClient or DesktopApp, they are not able to send DTMF (desk phone and mobile app work just fine). We have another 3CX machine for a sister company with the same settings on the users and trunk, and they are not having the same issue.

We tried changing the user settings but still the same issue no matter the option we select.

On the packet capture, RTP event is not being sent even though what seems to be the RTP G711U for the DTMF is being sent. Below is the image of the flow sequence for both the machine that works and the machine that doesn't.

Machine with DTMF Issue


Machine with no DTMF Issue

• 3CX Version: Enterprise Annual V18.0 Update 3 (Build 461)
• Server OS: Debian 10
• Is the 3CX Server Hosted and where? Hosted in Digital Ocean
• IP Phone Make/Model/Firmware version: WebClient v18.8.3.461 and DesktopApp v18.8.508
• Has the Firewall Checker passed: YES

Really appreciate any help.

 

[Alphabetic]

Do they both use the same AV?

 

[arillera]

Hi, yes they both use the save AV.
We recreated the issue using the same device and settings on both 3cx machines.

 

[Alphabetic]

You need to do a bit more troubleshooting. Does it happen on another browser? From another PC with no AV? From another internet connection?

 

[arillera]

Hi, yes we did test for different browsers, PCs, ISPs.
We tested for Chrome, Firefox, and Chromium with the issue being present in all browsers.
We tested all the staffs' PC with every change we made in the management console, but no successful DTMF.
We tried on a test VM hosted in our DC and the call did not go through as expected because of no AV.
We routed the calls through our 3 ISPs, but the same issue.
I tested in my home lab, still the same.

We did think at one point that the trunk could be the problem as we were providing the trunk and not the 3cx supported trunks but DTMF works when using desk phones and the mobile app.

 

[Alphabetic]

Are you able to do it if you can an IVR?

 

[arillera]

Hi, calling an IVR in our own system and voicemail menu works.
Curios thing tho is we're not able to capture those calls.

 

[Alphabetic]

Are you selecting all interfaces when capturing?

 

[arillera]

Sorry, kinda dumb of me. I did capture all interfaces but I just seem to not see it because it's going to itselt.

I do see DTMF being past when calling an IVR internally or when dialing the voicemail. Also works over the bridge trunk with our sister company's 3cx. Calls outside the system still do not work.

 

[Alphabetic]

I noticed when submitting the info you omitted your SIP provider. Are you using an unsupported one?

Try changing the order to use PCMA first. Failing that, you need to ask your provider.
If you go to an extension > phone prov > 3CX App

have you got this set to RFC2833?

 

[arillera]

Hi, our sister company which I am also a part of is the provider itself. Our sister company is a VoIP provider/reseller and only our 3cx machine is having issues with dtmf when using webclient or desktop app.

I switch our codec to PCMA temporarily as a test, but still the same issue.

The issue shouldn't be with our trunking system as desk phones and mobile app works, this is what is really curious about our issue.

 

[arillera]

Hi, we tried RFC2833, in-band, sip-info. also using other transports and RTP mode. still the same issue.

 

[arillera]

Found the issue, related to an already open thread.

https://www.3cx.com/community/threads/dtmf-event-duration-issue.113273/