nRF9160 not connecting to LTE network

[tl300]

What can prevent an nrf9160 from connecting to an LTE network?  I have custom boards with 9160s as well as a DK with a variety of SIM cards.  Most days, I have no issues with connectivity and establish connections within seconds.  However, some days (like today), I can't get a connection at all, or it takes about 30 minutes.  When this happens, I usually switch to the DK and run the Cellular Monitor.  If I do get a connection, it almost always takes 25-30 minutes.  Further, if I close the Cell Monitor session and start again, a new connection takes another 25-30 minutes.  I live in a major US city, so connectivity should be fine.  I also get the same behavior across different SIM providers too. 

[Michal]

Hello,

What are your NCS and Modem FW versions?

Did you experience this with sample applications on the DK as well, or only your custom code?

If yes, could you provide us with a modem trace showing that issue as well?

Best regards,

Michal

[tl300]

I have been using modem firmware versions 1.3.4 and 1.3.5, but mostly 1.3.5, the latest.  I experience connectivity issues with both custom and Nordic sample software.  Further, I also experience issues with both custom and Nordic hardware.  When I have issues, I switch to the nRF9160 DK with the sample asset tracker app installed and run the Cell Monitor in nrfconnect to monitor the connection.  When things are working, I get connections within seconds.  When they aren't, connections take about 30 minutes (which is well beyond the connection timeouts in my apps).  Right now, the RSRP and RSRQ values are listed as Fair and Poor, respectively, which is probably not a good sign.  However, I have observed such values without any issues in the past.  To be sure, I experience great connectivity most of the time.  Attached is a modem trace.  trace-2023-11-13T15-45-36.368Z.mtrace

[Michal]

Thank you, I will have to look more into that and I will get back to you.

Best regards,

Michal

[Michal]

Sorry for the delay. It sounds like you may be getting into the nRF9160 Modem Reset Loop Restriction mechanism.

Best regards,

Michal

[tl300]

Thanks for the reply.  Can you expand on the reset loop restriction mechanism?  It sounds like a feature designed for stuck devices.  I can envision hitting this with custom software on custom hardware during development, as I restart apps a lot, and often in not-so-clean ways.  However, it's unclear how I could hit this on an nRF9160DK running stock software and the Cell Monitor application.  I have certainly restarted the Cell Monitor app a lot at times, but I mostly start it and let it run to check connection times and monitor signal strength and quality.  As noted in my previous posts, connections usually take about 30 minutes for me.  Once I get one, I sometimes disconnect and start again.  This makes for about 2-3 resets per hour.  

[tl300]

Sorry for the delay.  The issue was (is) the Reset Loop Restriction.  As noted in the docs, the %XFACTORYRESET=0 AT command resolves the issue for me (in development).  What is still confusing is how I have been able to hit this mechanism on different hardware running different software with different workflows.  As I wrote above, I have an nRF9160 DK provisioned with stock software (ATv2 and modem firmware 1.3.5).  I basically use it with Cell Monitor as a test tool.  When I run into connectivity issues with my custom devices, I break out the DK to check the network.  What is confusing is that when I hit the Reset Loop Restriction with my custom devices, I also seem to hit it with the DK.  I find this a bit strange, because, again, they are different hardware, software, and workflows.  My workflow with the DK is basically that from the Quick Start Guide.