DTMF on v16 not working

[susit]

Hello,
we have upgraded our v15.5 installation to v16 after our Android phones upgraded their app.
So far everything works fine (and the new app is much better then the old one), except for DTMF.

Target is a door intercom (Commend/Schueco DCS) set up as an extension, speaking G.722 and understanding both SIP-Info or RFC 2833 DTMF.
It worked flawless on v15.5 and the old app.

Now it still works both with SIP-Info and RFC from all internal, wired phones (Yealink T48, Grandstream GXP2160), but not from the app on Android.
We have tried being on internal wifi and from external on 4G, tried switching on/off encryption, switching between SIP-Info and RFC, doesn't matter.

We are running Android 9 on Samsung S9 and Sony XZ2 phones with latest patch-level and app v16.1.0 According to play store it is the newest version.
3cx v16.0.3.676 locally on Windows Server 2016.

I've attached a trace with a call from a wired Yealink T48 on left side, correctly sending "1" as SIP-Info, and on the right side a trace from the app where the send SIP-Info is not reaching the target. But we are hearing a "beep" on the targets speaker when we try to submit a "1" from the app.

 

[StefanW]

Hi,

oddly that your Yealink is using SIP Info as it is not default as per template.
3CX APP and Yealink should both use RFC2833 as it is the most reliable form for DTMF transmission.
Did you also change this in the 3CX APP to be INFO for the extension in question?

 

[susit]

Hi,
thanks for your reply.
Firstly I have to correct myself, the Yealink is a T54S, not a T48. And the Android version shows up as 16.1.0.41 on our phones.

The Yealink was set to SIP-Info directly in the phone, and the app to that extension automatically selected SIP-Info. We've set it back to RFC (default) for both phone and app, but that doesn't change anything about the problem.
All wired phones no matter if set to SIP-Info or RFC are still working fine with v16, but all connected apps won't do DTMF. We only hear a "beep" on the targets speaker.

Attached a trace with a phone and app set to RFC. From a wired phone (left side) RFC-DTMF reaches the target, right side the app (same extension) set to RFC doesn't show up any rtpevents and I've pressed a key and waited multiple times (sip.Method==Invite just to show up anything at all in the trace).

 

[nb]

Can you try another target?
You can try for example to call a bank number and press 1 and see if the DTMF's with that number work.
DTMF has not changed for years. For sure the number you are calling is either a "weak" provider or the exchange used has some incompatibility.,

 

[JohnS_3CX]

1. Run a capture from the management console
2. Call a deskphone extension from your Android
3. Answer it and then press a few number keys on your Android 3CX dial pad
4. End call, and end the capture and open it.

In the the SIP flow sequence, you should see the PBX IP sending DTMF to the deskphone IP as RFC 2833 RTP Events. If this works then your Android app is configured correctly and behaving right.



If not then ensure that you reprovision the Android client from scratch after ensuring it is set to the correct DTMF format:



Repeat the test as above to ensure you see the DTMF in the capture.

NOTE: You will not see the Android device IP anywhere in the capture, because it talks to the PBX via an encrypted tunnel

 

[susit]

Hi John,
appreciate your help.

I've attached a screenshot of two traces I did in the management console.
On the left side I've called extension 02, a Yealink T54S deskphone. As expected the DTMF tones are send out.
Then I called extension 05, the intercom (IP .51) in question. Again I pressed "1" multiple times, but no DTMF shows up in the trace.
I called up other numbers from the app (bank, microsoft product activiation hotline..), everytime the DTMF tones are send and recognized.

I don't understand that I cannot even see the PBX sending out DTMF-rtpevents, even if the target is not responding, when calling that extension from the app?

 

[JohnS_3CX]

What device is extension 05? Is it a supported device?

To understand why you cannot see the STMF events being sent by the PBx, look at the SDP send back to the PBX by the intercom device then, during the invite reply. Did the device agree to any DTMF format? If not then then the PBX will not send anything to it that was not agreed in the call setup.