Troubleshooting Tip: How to force a 4G LTE only or a 5G only connection via AT!SELRAT command on the FortiExtender-511G

By default, the AT!SELRAT setting is Automatic, and the modem allows the following values:

execute modemfw AtTest modem1
open tty /dev/ttyUSB0
AT!SELRAT=?

!SELRAT: Index, Name

00, Automatic

01, WCDMA Only

06, LTE Only

11, WCDMA and LTE Only

20, NR 5G Only

21, LTE and NR 5G Only

22, WCDMA and NR 5G Only

ATSELRAT

If the FortiExtender is not able to establish a 4G LTE or a 5G connection using the 'Automatic' setting, try forcing the modem to establish LTE only or a 5G only connection, and verify whether the data connection works using either connection mode (LTE only or 5G only):

1. If the SIM Carrier has a poor 5G coverage in the area where the FortiExtender is deployed, force LTE only connection and verify if the modem establishes a 4G LTE connection, using the 'get modem status' command:

execute modemfw AtTest modem1

AT!SELRAT?

AT!SELRAT=06

• Use 'AT!SELRAT?' command to view the current RAT config.
• Press 'Ctrl+C' to exit the AT command prompt and see the 'get modem status' output for connection status.
• Reboot the FortiExtender (execute reboot) and wait for up to 5 minutes to see if the modem connection status changes.

LTE only

2. If the SIM Carrier has a good 5G coverage, but the FortiExtender is not able to establish a 5G connection automatically. Force 5G only connection and verify if the modem connects to 5G connection using the 'get modem status' command:

execute modemfw AtTest modem1

AT!SELRAT?

AT!SELRAT=20

• Use the 'AT!SELRAT?' command to view the current RAT config.
• Press 'Ctrl+C' to exit the AT command prompt and see the 'get modem status' output for connection status.
• Reboot the FortiExtender (execute reboot) and wait for up to 5 minutes to see if the modem connection status changes.

NR 5G only

3. If the above changes do not help, revert the AT!SELRAT settings to the default 'Automatic' as shown below:

execute modemfw AtTest modem1

AT!SELRAT?

AT!SELRAT=00

• Use 'AT!SELRAT?' command to view the current RAT config.
• Press 'Ctrl+C' to exit the AT command prompt and see the 'get modem status' output for connection status.
• Reboot the FortiExtender (execute reboot) and wait for up to 5 minutes to see if the modem connection status changes.

Automatic

Related articles:

• Troubleshooting Tip: How to configure 5G SA, NSA (ENDC) settings via AT!RATCONFIG command on the FortiExtender-511G
• Technical Tip: How to configure and debug 4G LTE connection issues on FortiExtender (FEX)