User in Guernsey cannot connect to the network with NRF9160

[lzpons]

Hi,

I have a customer in Guernsey that received one of our Thingy91 hubs and he's not able to connect.

Here is some troubleshooting facts :

- when he moves to London the device connects successfully

- when he looks to the available networks locally with his iphone, there is actually an LTE network see snapshot.

- if he puts our SIM in his phone, it works properly establishing a connection.

- when he looks to the available networks through the Thingy:91 with the LTE Link Monitor using AT+COPS? command : nothing is reported

What may be wrong with this location? are there "special" LTE networks that the NRF9160 cannot see?

What troubleshooting would you suggest to move ahead?

Thanks for your help

LP

[Didrik Rokhaug]

Hi, and sorry for the late reply.

What board are they using?

lzpons said:

he took the trace with a NRF DK board

lzpons said:

mg_app_bl/debug/thingy91_asset_tracker_v2_debug_2022-12-08_188a1603.hex

That file is for a Thingy:91, not a DK.

lzpons said:

Hologram covers Guernsey with Sure carrier

I am not able to see if this agreement supports LTE-M and/or NB-IoT or not. It might not be covered.

Getting a modem trace with the Jersey Air SIM would also be useful.

[lzpons]

 Didrik Rokhaug below are two tests traces run by the customer on Thingy91 board (no DK) using the thingy91_asset_tracker_v2_debug_2022-12-08_188a1603.hex app together with a locally purchased Jersey Airtel SIM.

- First test runs app in default mode

trace-2023-02-08T19-14-25.294Z_JerseyAirtel_SIM.bin

trace-2023-02-08T19-14-25.294Z_JerseyAirtel_SIM.bin

- Second test has been forced to nbiot

trace-2023-02-09T10-28-05.811Z_JerseyAirtel_SIM_NBIOT_forced.bin

AT%XSYSTEMMODE=0,1,0,0
AT+CGDCONT=0,"IPV4V6","cdp.iot.t-mobile.nl"
AT+COPS=1,2,"23403",9
AT+CFUN=1

trace-2023-02-09T10-28-05.811Z_JerseyAirtel_SIM_NBIOT_forced.bin

As a reminder (because there is already a long tread here) what we are seeking is to undersdand

- is there or not any LTE-M network available we can connect to?

- otherwise can we connect to nb-IoT as an alternative?

- If none are available what is the suspected reason?

Hope you can diagnose something.

[Didrik Rokhaug]

In the JerseyAritel_SIM trace, manual network selection requested to 208 20 (Bouygues Telecom) which is not found. Could you try to send AT+COPS=0 (set automatic network selection), then AT+CFUN=0 (store the settings to non-volatile memory), and then reset the device?

In the JerseyAirtel_SIM_NBIOT_forced trace, this was the teams analysis:

Not forced to use NBIOT (looking at the trace, it looks like you tried to set NB-IoT only mode  while the modem is running. This is not allowed. %XSYSTEMMODE must be used while the modem is offline), but forced (i.e. manual network selection) to 234 03 (Jersey Airtel). There is one tracking area available (in NBIoT), but network rejects Attach with cause #15 "No suitable cells in tracking area". This means that device is not allowed to operate in this tracking area with this SIM subscription. In the end of the log modem finds another tracking area and initiates Attach procedure. This time the Attach is not successful because signalling connection is lost before receiving Attach Accept. This is a bit unexpectable, because mapped RSRP was 47 at the time the cell was found. Although, there were some change in radio conditions because at first this cell was not found at all. Assuming the SIM subscription should work with Jersey Airtel, for some reason network releases the RRC connection in the middle of Attach procedure. We don't know the reason, but have seen similar now and then.

Looking at the traces, it also looks like you are trying to set the APN manually. Are you sure you are using the pre-compiled applications, and not a custom one?

It might also be that these settings has been stored in the modem previously. You can try to delete all saved data in the modem with the %XFACTORYRESET AT command. Resetting the user data should be enough. Note that this command also must be used while the modem is offline, so it can be a good idea to use AT+CFUN=4 first.

[Didrik Rokhaug]

As a way forward, the modem team suggest you ask Airtel if the device/SIM card is supposed to be able to connect at that location:

I can see from IMSI that the home network is 234 03 Jersey Airtel. From log we can see that tracking area 0A33 gives the Attach reject #15 "No suitable cells in tracking area". Customer could ask from the operator why their SIM subscription is not allowed to work in that tracking area. In another tracking area (09CF) network releases the RRC connection before Attach Accept is received, which seem not to be due to signal quality from modem point of view. This kind of unexpected RRC connection releases we have seen earlier but we have no workarounds for that and we don't know why this happens. But I think this is not network's way to reject the device, meaning that without this unexpected release the Attach might even get accepted.

[lzpons]

Hello Didrik,

Thanks for the latest answer. It was helpful. We went back to the SIM provider asking them what their SIM was capable. It seems that not all the support people at Airtel was aware SIM was supporting only data (on a mobile) and that this is not the same than data for M2M. Finally we found an expert in their team who advised us properly and providing a SIM that supports NB-iot in their own network (Airtel).

So as a summary, this was the main issue with all this support ticket : The SIM was not connecting because had the wrong "configuration". New SIM specially focused on M2M and nb-iot is able to connect.

(still facing some small issues on getting time from the network, but this is another topic.

I believe can close this ticket.

Thanks A LOT for your help and patience.

Lorenzo