How to

[Jeffery]

Hi Nordic team

At sdk connect sample/mqtt_simple, it called lte_lc_init_and_connect() to connect NBIOT or LTE-M.

If this call was not successful, could we read error code to analyze the root cause?

For example,

1. SIM card interface issue.

2. Base station didn't response.

3. The strength of signal from base station was too weak to communicate.

4. And so on.

Thanks.

Jeff 

[Didrik Rokhaug]

Hi,

When using lte_lc_init_and_connect, there unfortunately aren't much other feedback than ETIMEDOUT.

However, if you register an event handler, you can get more information.

SIM card issues usually causes a +CEREG: 90 notification. If the device was not allowed to connect to the networks, you can find the reject cause in the +CEREG notifications, and the registration status will usually be 3 or 4.

Using the at_notif library, you can also subscribe to %MDMEV notifications, which also can contain useful information.

Best regards,

Didrik

[Jeffery]

Hi Didrik

For CEREG, at mqtt_simple sample, it set "AT+CEREG=5" to modem. So, subscribes CEREG notifications as below format according to at commands spec. Notification shall have cause type and reject cause defined at 3GPP 24.301 Annex A.

I checked 3GPP 24.301. I did analyze the failure reason in much detail.

So, my question is. Did Nordic really implement the "cause type" and ""reject cause" at CEREG notifications as LTE

failed to connect? If yes, I think we can use these information to get why LTE cannot be connected.

Jeff

[Jeffery]

Hi Didirk

Then, I tried DK at a shielding room not ot connect the cell site.

After connecting timeout, it got CEREG notifications with reject cause 11 and 15.

11 => PLMN not allowed

15 => No suitable cells in tracking area

[Didrik Rokhaug]

How shielded is your shielded room?

The log shows that it finds a network, and tries to attach to it, but is not allowed for the reasons you described.

If it didn't find any networks the tac and ci fields should be "FFFE" and "FFFFFFFF", and more importantly the %CESQ notification fields should be 99 for the first two, and 255 for the rest.