Mobile data connection troubleshooting

Summary

This is a quick guide to help in the debugging process of a router if encounters issues with mobile data connection.

Preparation

First, to establish a data connection only through mobile module on RUT, you need connect to router via CLI/SSH (use SSH software such as PuTTY client):

CLI/SSH username: root
CLI/SSH password: <your router’s password>

Connect to mobile module of the router:

... 
root@Teltonika:~# ifdown ppp
root@Teltonika:~# /etc/init.d/gsmd stop
root@Teltonika:~# microcom /dev/modem_cmd
+QCSQ: "LTE",47,-75,166,-10
+QCSQ: "LTE",47,-75,161,-10
+CREG: 1,"008B","012CD17",7
...

You probably won't see anything when you type commands, and that’s because the screen echo may be disabled. ATE1 command will enable it so that you can see what you write. AT+QCSQ=0 and AT+CREG=0 command stops showing unnecessary output:

...
ATE1
OK
at+qcsq=0
OK
at+creg=0
OK
...

Check communication (wait for the module to respond OK):

... 
AT
OK
...

Debugging process

If PIN is required, initialize modem with your PIN code:

...
AT+CPIN="xxxx"
...

Use command AT+CPIN to query SIM card status:

...
AT+CPIN?
+CPIN: READY
...

Note: Reboot the module if it fails to identify SIM

Use command AT+CREG to check GSM connection:

...
AT+CREG?
+CREG: 0,1
OK
...

Note: OK means that the module has registered on CS domain service

Use command AT+CGREG to check PS Service:

...
AT+CGREG?
+CGREG: 0,1
OK
...

Note: OK means that the module has registered in UMTS/LTE network

9. Configure APN, user name, password and auth type by AT+QICSGP • AT+QICSGP=<contextID>[,<context_type>,<APN>[,<username>,<password>)[,<authentication>]]] <context type> The protocol type (1 – IPV4; 2 – IPv6). <context id> The range is 1-16. <authentication> The authentication methods (0 – NONE; 1 – PAP; 2 – CHAP; 3-PAP or CHAP). Example: AT+QICSGP=1,1,"APN_Name","","",1

10. Activate a PDP context: • AT+QIACT=<contextID>

11. Query IP Address of the PDP context: • AT+QIACT? (*Try and activate a PDP context a few times. If failed, then reboot the module). 12. Open connection: • AT+QIOPEN (*If failed – deactivate PDP context - use command AT+QIDEACT=<context ID> to deactivate PDP context.) 13. Use AT commands to ping a Remote Server • AT+QPING=1,"8.8.8.8"

1 –The context ID. The range is 1-16;
8.8.8.8 - The host address in string type. The format is a dotted decimal IP address.

Response: • If ping a remote server successfully, response: OK (means that the module works properly) • If there is any error, response: ERROR (means the problem is in the module)

Example fo the provided configuration: