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 commands 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

---

• Use command AT+QICSGP to configure APN, user name, password and auth type:

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

...
AT+QICSGP=1,1"bangapro","","",1
OK
...

---

• Use command AT+QIACT=<contextID> to activate a PDP context:

...
AT+QIACT=1
OK
...

---

• Use command AT+QIACT? to query IP Address of the PDP context:

...
AT+QIACT?
+QIACT: 1,1,1,"88.77.66.55"
OK
...

Note: try and activate a PDP context a few times. If failed, then reboot the module.

---

• Use command AT+QIOPEN to open connection:

...
AT+QIOPEN
OK
...

Note: if failed – deactivate PDP context - use command AT+QIDEACT=<context ID> to deactivate PDP context.

---

• Use command AT+QPING to ping a Remote Server:

...
AT+QPING=1,"8.8.8.8"
OK
+QPING: 0,"8.8.8.8",32,54,255
+QPING: 0,"8.8.8.8",32,30,255
+QPING: 0,"8.8.8.8",32,35,255
+QPING: 0,"8.8.8.8",32,34,255
+QPING: 0,4,4,0,30,54,37
...

1 –The context ID. The range is 1-16;

8.8.8.8 - The host address in string type.

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

Example for the provided configuration

...
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
+QCSQ: "LTE",47,-75,156,-10
+CREG: 1,"008B","012CD17",7
AT+QCSQ=0
OK
+CREG: 1,"008B","012CD0D",7
+CREG: 1,"008B","012CD17",7
AT+CREG=0
OK
AT
OK
...

...
AT+CPIN?
+CPIN: READY
OK
AT+CREG
OK
AT+CREG?
+CREG: 0,1
OK
AT+CREG
OK
AT+CGREG?
+CGREG: 0,1
OK
AT+QICSGP=1,1"bangapro","","",1
OK
AT+QIACT=1
OK
AT+QIACT?
+QIACT: 1,1,1,"88.77.66.55"
OK
...

...
AT+QIOPEN
OK
AT+QPING=1,"8.8.8.8"
OK
+QPING: 0,"8.8.8.8",32,54,255
+QPING: 0,"8.8.8.8",32,30,255
+QPING: 0,"8.8.8.8",32,35,255
+QPING: 0,"8.8.8.8",32,34,255
+QPING: 0,4,4,0,30,54,37
...