DTMF Functionality on RUTX50 in 4G Network

NETWORKING SOLUTIONS
1

Hello,

I am using your Teltonika RUTX50 device for a specific automation process which involves:

Receiving an incoming call from a predefined number,

Automatically answering the call and sending DTMF signals,

Ending the call and initiating a return call with further DTMF commands.

All functions have been properly tested and work correctly when the router is connected to a 5G network. However, a serious issue occurs when the router is connected to a 4G network:

The call cannot be established — it appears as if the line is busy.

The router does not answer the call.

DTMF functionalities do not work, even though the modem port (/dev/ttyUSB2) is present.

I have tried using all available AT commands, different modem ports, and access methods (SSH, custom scripts, startup scripts), but the functionality stops as soon as the router switches from 5G to 4G.

I kindly request your technical support or guidance on how to:

Enable the same functionality on a 4G network.

Thoroughly determine the difference in modem behavior between 4G and 5G modes.

Obtain a list of active modem ports and their functions depending on the network.

Best regards,

3

Good afternoon,

Ensure that VoLTE is enabled on your RUTX50 when operating on 4G. VoLTE allows voice calls over the LTE network, which is essential for call handling and DTMF signaling on 4G. The Mobile settings page in RutOS lets you configure this, with options like Auto, On, or Off for VoLTE. Set it to “On” or “Auto” to ensure voice calls are supported on 4G

Confirm the device is properly locked or set to use compatible LTE bands (Teltonika Band lock). Sometimes, the device may connect to a 4G band or mode that does not fully support voice calls or DTMF.

Regards,
Arturas