3CX DTMF Inband and RFC2833 error

[johnvam]

Hello!

We have a serious problem with DTMF. We are from Voiceland which is a local VoIP Provider in Greece. We have no issues at all but we have DTMF issues when we make calls to other telephone numbers which belong to specific Greek carrier. After a lot of research we figured that all the carries in Greece work with RFC2833 but this specific carrier works with Inband.
We have provisioned Yealink and SNOM I Phones to our 3CX and when we call to numbers of this specific carrier DTMF is not passing.... becuase uses INBAND. When we make calls to any other destination DTMF works fine because they use RFC2833.

My question is, 3CX Media Server cannot listen to any DTMF mode? Also I have to mention that I have enabled "PBX Delivers Audio" to both extensions and SIP Trunk.

On traces we send telephone-event when we make outbound calls. All the other providers in Greece give back to us telephone-event except this carrier which do not support RFC2833 !!!

Any idea?

 

[JohnS_3CX]

Hello!

We have a serious problem with DTMF. We are from Voiceland which is a local VoIP Provider in Greece. We have no issues at all but we have DTMF issues when we make calls to other telephone numbers which belong to specific Greek carrier. After a lot of research we figured that all the carries in Greece work with RFC2833 but this specific carrier works with Inband.
We have provisioned Yealink and SNOM I Phones to our 3CX and when we call to numbers of this specific carrier DTMF is not passing.... becuase uses INBAND. When we make calls to any other destination DTMF works fine because they use RFC2833.

Hi @johnvam

If the provider does not support RFC2833, then there is nothing you can do to make them "see" it, you will send the RTP events and they will completely ignore them. This is a problem on their part unfortunately.

My question is, 3CX Media Server cannot listen to any DTMF mode? Also I have to mention that I have enabled "PBX Delivers Audio" to both extensions and SIP Trunk.

This is not a media server matter, you are probably thinking of IVRs which are designed to listen for DTMF events. They can understand in-band too but they only "hear" the events, they don't send them back

On traces we send telephone-event when we make outbound calls. All the other providers in Greece give back to us telephone-event except this carrier which do not support RFC2833 !!!

Yes, the other providers are following standards as they should, and not relying on in-band alone

I can think of a solution for you but I it's not a good solution to recommend, it's as a last resort if you are forced to make calls to that provider and it will probably make your DTMF on the PBX less reliable in general. You need to set your actual phones to send in-band DTMF. If the phone sends in-band, it's part of the audio stream now and the other side will hear it.

Now the caveats: However, now your DTMF will be less accurate because it relies on detection via audio. It may make your own IVRs and calls to other outside IVRs less reliable. And, even for than one problematic provider, if you call one of their customers which has an IVR that does not detect the in-band well, your results may vary.