NB-IOT not connecting on nrf9161 DK

[HoovinSchoovin]

Hi, 

I have been having quite a lot of issues around connectivity and my device, all of which at this point has stemmed from MNO blocking activity from MVNO's (here and here). 

I have LTE-M working when in an areas which supports it, however, i cant ever seem to connect to the NB-IOT networks despite all my efforts. I would very much appreciate walking through the steps i have taken to check if there is anything that i am not thinking of. 

1. After booting up AT_CLIENT, I have ensured that there is a nbiot network in my area: 

> AT+COPS=?
+COPS: (1,"","","21901",9),(1,"","","21910",9)

Am i right in thinking the 9 denotes the network is nbiot?

2. I have ensured my system mode allows for nbiot

> AT%XSYSTEMMODE?
%XSYSTEMMODE: 0,1,1,0

3. I checked the sim im using, and it has nbiot where i currently am situated (Croatia)


4. After no luck, i checked some posts (here) and opted in for legacy PCO instead of ePCO (i did this with CFUN=0 then went to CFUN=1)

> AT%XEPCO=0
OK

After considerable time, the network is still not connected as shown here:

> AT+CEREG?
+CEREG: 0,2

In cellular monitor, the activity status is: "Not registered, attaching or searching". 

Below is my trace file:
trace-2024-09-02T23-02-48.261Z.mtrace

Any help or just suggestions of what to check next would be greatly appreciated. 

SDK Version: v1.6.1
Sim card: Emify (same behaviour on Onomondo too)
Location: Croatia, Dubrovnik (Same has occured in Edinburgh)
Board: NRF9161 DK

Thank you :)

[dejans]

Hi,

You could look at COPS set command. Based on the nRF9160 AT Commands Guide v2.4, COPS set command has 4 parameters which you can choose. For example, you could use it like this for NB-IoT

AT+COPS=1,2,"21901",9

According to documentation, the command configuration is stored in NVM approximately every 48 hours and when the modem is set to minimum functionality mode with the +CFUN=0 command.

Best regards,
Dejan

[HoovinSchoovin]

Hi Dejan,

Thanks for getting back to me. After trying to set the COPS, I got this. I also tried AWS sample and could not get access to internet too. 

> AT+COPS=1,2,"21901",9

OK
> AT+CFUN=0

OK
> AT+CEREG?

+CEREG: 0,4

OK

> AT+CFUN=1

OK
> AT+CEREG?

+CEREG: 0,4

OK
> AT+CEREG?

+CEREG: 0,2,"0CEE","0868235C",9

OK

** AFTER over 10m waiting**

> AT+CEREG?

+CEREG: 0,2,"0CEE","0868235C",9

OK

I've attached the cell monitor screenshot below:


Also, here is the wireshark PDF - note the "DLInformationTransfer-NB, Attach reject (PLMN not allowed)". Could this be the error? :

wireshark_sharkfin-gcjnvzvmst8T4NT2.pcapng.pdf

Any other ideas, please let me know - very much appreciate the help 

[dejans]

Hi,

You can look at AT+CEREG set command (nRF91x1 Cellular AT Commands) and try to set it to value 4 or 5. This should provide more information about the reject cause in your case.
You could also try to set automatic network selection mode (code 0) in the +COPS command.

Best regards,
Dejan

[HoovinSchoovin]

Hi Dejan, 

Thanks for those tips. 

After setting AT+COPS=0, I managed to register to the network .

+CEREG: 5,5,"9D6C","000FA3B6",9,,,"11100000","11100000"

One of the reasons why i had not explored doing that more was this article: here. 

When trying the AWS IOT core, with no changes except for adding in my broker and clientIDs (+certs), I am unable to access the network still. I am guessing this is because the code is not using the AT+COPS=0 command. Any idea how I should proceed. Should I hardcode a COPS=0 in the AWS library somewhere? 

Thanks again for your continued help. 

Kind regards, 
Sam

[dejans]

Hi Sam,

HoovinSchoovin said:

When trying the AWS IOT core, with no changes except for adding in my broker and clientIDs (+certs), I am unable to access the network still. I am guessing this is because the code is not using the AT+COPS=0 command. Any idea how I should proceed. Should I hardcode a COPS=0 in the AWS library somewhere?

Do you have a log which you could share?

Best regards,
Dejan