DTMF Issues

[lunartechnologies]

Hello,
I have this bizarre DTMF issue on one of my 3CX with a voip.ms SIP trunk.

I manage 2 3CX. Both of them have a voip.ms SIP trunk(Both subaccounts of the same account).
The settings are exactly the same on both 3CX for the sip trunks.
The settings for DTMF on voip.ms are the same for both as they are subaccounts of the same account.
For one of them, the DTMF works perfectly. For the other one, they do not get sent.

I also have a wavix sip trunk on the one that does not send the DTMF with voip.ms, And it works well with wavix.

So to resume:

PBX1 -> voip,ms No DTMF on outbound calls.
PBX1-> wavix DTMF Ok
PBX2 -> voip.ms DTMF Ok

I did a packet capture on the PBX that is not sending the DTMF and it seems ok:

I compared the option settings on both 3CX and they are exactly the same.

Does anyone have any ideas about what else it can be?

Thank you

 

[leejor]

Is the DTMF Method being use on all of the trunks the same? Have you looked at the calls in the Activity Log (Verbose)?
Did this issue just start, or has it never worked?

 

[Alejandro_3CX]

Hi @lunartechnologies for outbound calls the 3CX adds the telephone-event 101 codec to the SDP for the transmission of DTMF tones over RFC2833, the SIP Trunks in the 200 OK should include the same.

3CX does not by default send in-band DTMF tones, it relies on the registered endpoint, so if the endpoint does send in-band DTMF tones, 3CX will relay it.

 

[lunartechnologies]

Is the DTMF Method being use on all of the trunks the same? Have you looked at the calls in the Activity Log (Verbose)?
Did this issue just start, or has it never worked?

Hi.
Yes same settings on both.
I have but I did not see anything interesting about DTMF there. Should I look for something in particular?
It has never worked on that PBX it's a new install.

Hi @lunartechnologies for outbound calls the 3CX adds the telephone-event 101 codec to the SDP for the transmission of DTMF tones over RFC2833, the SIP Trunks in the 200 OK should include the same.

3CX does not by default send in-band DTMF tones, it relies on the registered endpoint, so if the endpoint does send in-band DTMF tones, 3CX will relay it.

From what I can see they are the same indeed :
Request :

200:

In both cases, I'm using the browser base 3CX client and 3CX mobile app.
Is there some setting there that I need to change so they send the DTMF tones?

 

[YiannisH_3CX]

No additional settings are required. Make a new capture from the PBX and make a test call. Send a few DTMF digits and hang up the call. Make a note of what you pressed.
Stop and save the capture. Open it using Wireshark and filter by "rtpevent".

Let us know what you find.

 

[lunartechnologies]

Looks like it's sending to voip.ms :
I compared the capture between my 2 3CX and the behaviour is exactly the same.
I even, for fun, registered the other 3CX on the same subaccount as the one with the issue.
And the DTMF are still working.

 

[YiannisH_3CX]

In the VoIP,ms portal there should be an option for DTMF under Account Settings / Advanced. Make sure that the option is set to either Auto or RFC2833.

 

[lunartechnologies]

Yes, it's already at Auto, and I tried with RFC2833.
As I said when I tried with my other 3cx on the same account everything worked fine.

 

[YiannisH_3CX]

So to recap:

• 2 3CX systems, 1 is working and 1 is not.
• Both SIP accounts work on the working 3CX installation.
• The behavior of the 2 systems is identical in regards to sending DTMF out.

So both systems work and both SIP accounts work. The affected 3CX is sending DTMF signals out as seen in the pcap but are never received.
So the only thing that remains is the network configuration. The first step is to make sure the firewall checker passes. Then run a capture on the firewall and see if the DTMF signals are sent out. If that also checks out then contact VoIP.ms and ask them what they see from their end.