Solved Inbound dtmf digit duplicated

[han0522]

I'm using 3cx v16 hosted on AWS and Telnyx as the sip trunk. I'm using 3cx in a small business environment (migrating from a very old phone server). While I wait for our business number to port over to telnyx I have setup call forwarding via our phone company. This works well except for one thing: inbound dtmf. For example, if I enter 318 during our IVR prompt (to directly reach extension 318) extension 331 will ring. After looking through logs and packet capture it appears like an inband tone and an rfc2833 packet are being received by 3cx; thus, what 3cx "sees" when an inbound caller types 318 is 331188. I assume 3cx recognizes three digits and immediately forwards, thus sending the caller to extension 331.

I've tested the above with Telnyx's DTMF setting as inband, rfc2833, and sip info, all with the same results (typing 318 reaches 331). I've only packet captured when Telnyx was set to use rfc2833. When I call the sip trunk number directly (skipping the call forward) everything works as expected, so I figure my local phone company is adding the inband tone and that gets forwarded through telnyx. Telnyx then adds dtmf as well (default is rfc2833, but as stated above I've tried inband and sip info as well) and the resulting duplicated 'tone' is received by 3cx.

I should note that I am new to 3cx and voip so my assumption could easily be wrong.

So I'm looking for a temporary solution while I wait for this port to go through. My initial thought was to somehow tell 3cx to ignore rfc2833 and only listen for inband - once the port goes through I would undo this setting.

Has anyone encountered this problem? Is there a way to temporary ignore inbound rfc2833?

• 3CX Version 16.0.8.9
• Server OS, Debian 9
• Is the 3CX Server Hosted and where? Amazon web services
• IP Phone Make/Model/Firmware: Not relevant, but Yealink T46s and Yealink T42s
• Provisioning Method: Local / VPN / STUN / SBC: SBC
• Trunk Provider or Gateway Make/Model: Telnyx
• Has the Firewall Checker passed: YES
• Are custom Phone Templates being used: YES

Thanks
Chris

 

[Evolute IT]

3CX only supports RFC DTMF for good reasons. I would contact Telnyx to ask if they see those double DTMF as well. If they do, you can then contact your local phone provider. If not, then the issue isn't from there.

 

[leejor]

Changing your trunk Codec (if supported by your provider), to something that does not pass audio DTMF easily (usually something other than G711) might work temporarily, however, it may introduce other audio problems.

 

[han0522]

Changing your trunk Codec (if supported by your provider), to something that does not pass audio DTMF easily (usually something other than G711) might work temporarily, however, it may introduce other audio problems.

Oh, that's perfect. Changed telnyx to use g729 and just tested it and dtmf is now working as expected (i.e. inband is not passing, only 2833).

Many thanks!
Chris

 

[YiannisH_3CX]

Glad to see the issue has been resolved. To add to this, the upcoming V18 has some improvements that will greatly reduce the likelihood of this happening.