2G EE call to 3CX DDIs - unreliable DTMF

[wesThreecx]

Hello,

We have recently got an issue where a 2G EE SIM in an intercom will not always respond to DTMF inputs. This has been working reliably for several years.

The Videx intercom with a 2G EE SIM called a 3CX DDI and the called party can press 3 to open the door. The voice quality is fine but the DTMF input is now working about 50% of the time.

If we get the Videx to call another Mobile device as the called party, DTMF code 3 always works.

3CX is self hosted Version 20.0 Update 7 (Build 1080 Release)

Appreciate this might well be nothing to do with 3CX but it is odd that the Videx will always respond to DTMFs generated by another mobile phone. For testing we have used 3CX mobile clients and desk phones - all of which previously worked without fault.

Thank you in advance for any insights.

 

[leejor]

I would want to confirm, if possible, that some calls are not able to use a low bit-rate codec. That will definitely have an effect on DTMF tones.

 

[KyriacosS_3CX]

Any chance it was piggy-bagging on O2 signal and the 3G cut-off caught up with it (yes it's a 2G device but this things tend to be complicated)?

I would also ask your SIP Trunk provider if they had any recent changes, it might not be on the trunk to you, but how/through who they hook up with EE.

 

[wesThreecx]

Any chance it was piggy-bagging on O2 signal and the 3G cut-off caught up with it (yes it's a 2G device but this things tend to be complicated)?

I would also ask your SIP Trunk provider if they had any recent changes, it might not be on the trunk to you, but how/through who they hook up with EE.

Not sure how we establish what is involved with the 2G SIM initiated calls. Will a 3CX packet capture of the failed DTMF attempts be useful to our trunk provider?

 

[wesThreecx]

I would want to confirm, if possible, that some calls are not able to use a low bit-rate codec. That will definitely have an effect on DTMF tones.

Will a 3CX packet capture of the failed DTMF attempts help us understand if this is a factor?

 

[leejor]

Access to the 3CX Activity Log, set to Verbose, would show the choice of Codecs in the initial Invite. However, that doesn't guarantee continuity for the entire call, as you have no control over what the provide decides to do, along the way.

Is it possible to swap SIMs, and test using another provider?

 

[wesThreecx]

Access to the 3CX Activity Log, set to Verbose, would show the choice of Codecs in the initial Invite. However, that doesn't guarantee continuity for the entire call, as you have no control over what the provide decides to do, along the way.

Is it possible to swap SIMs, and test using another provider?

We did a 3CX packet capture today and saw there was G.711 PCMA between our 3CX server and the Trunk provider. The capture also showed us pressing 3 on the phone ( pressed a few times ) which were recorded as RFC 2833 RTP Event DTMF Three. The payload type being 101. None of these DTMF tones were acknowledged by the remote intercom.

If I read this correctly from https://www.cisco.com/c/en/us/suppo.../223118-identify-dtmf-events-in-a-packet.html then this is in-band DTMF which is usually reliable with the uncompressed G.711 codec.

I will swap the SIMS next - do not have a suitable one to hand.