Long disconnects with empty PDP on nrf9160

RE: Long disconnects with empty PDP on nrf9160

nicolae.georgescu — Sat, 29 Mar 2025 18:21:14 GMT

Thanks a lot! The blacklising of an operator would be set by 1NCE, the SIM only does a local save that can get in the way if in the future we remove the blacklisting from 1NCE side and the sim keeps the cache. But from your test it seems a restart is enough and the sim removes the cache, so that is definitely easy to do!

RE: Long disconnects with empty PDP on nrf9160

Achim Kraus — Sat, 29 Mar 2025 18:19:10 GMT

I retested the "forbidden PLMN list" with a 1NCE SIM. That clears the list on power off (at+cfun=0). So you would need to rewrite it on power on.

RE: Long disconnects with empty PDP on nrf9160

Achim Kraus — Sat, 29 Mar 2025 06:54:35 GMT

[quote userid="109160" url="~/f/nordic-q-a/120262/long-disconnects-with-empty-pdp-on-nrf9160/529616"]We used to be locked on band 3 that worked well, and in >1 year we only experienced short disconnects that were fixed by either soft retries or rebooting the device.
Couple of months ago the operator started removing band 3 and adding band 20. When we removed band locking the device can connect to other operators (Vodafone besides Orange).[/quote]

If it works for you with only 1 operator, then "CONFIG_LTE_LOCK_PLMN_STRING" (or 'AT+COPS=1,2,"<your plmn>" ') may do the job.

RE: Long disconnects with empty PDP on nrf9160

Achim Kraus — Sat, 29 Mar 2025 06:47:39 GMT

[quote userid="109160" url="~/f/nordic-q-a/120262/long-disconnects-with-empty-pdp-on-nrf9160/529617"]Indeed there is a blacklist on the SIM. The question 2 is about how to reset the saved blacklisted operator on the sim.[/quote]

There are AT cmds ("AT+CRSM") to read and write such list from and to the SIM by the app. It requires AFAIK some know-how about the SIM card (e.g. 3GPP TS 31.102, I've implemented a set of functions for my client some time ago).

Some SIM card even delete the blacklist in a power-off/on cycle, there you need to frequently rewrite that list. If I remember well, the 1NCE SIM does so, so you mayl need to write it again after each modem restart.

[quote userid="109160" url="~/f/nordic-q-a/120262/long-disconnects-with-empty-pdp-on-nrf9160/529617"]By reboot i mean from the code, we do a division by zero so it reboots.[/quote]

Strange solution. There is a "sys_reboot" function (may require CONFIG_REBOOT).

[quote userid="109160" url="~/f/nordic-q-a/120262/long-disconnects-with-empty-pdp-on-nrf9160/529617"]Modem factory reset doesn't sound like something the device could do on it's own[/quote]

There are functions for that, first call "lte_lc_power_off" and then "lte_lc_factory_reset".

Anyway, that is just an idea, it may or may not help. In my case it helps to bring back some "blocked devices", but that's very rare (only few device, less than once every 150 days). More often (in my experience more cause by other MVNOs, not 1NCE) a "lte_lc_power_off" and "lte_lc_power_on" again helps to get over some sticky network rejection codes.

RE: Long disconnects with empty PDP on nrf9160

nicolae.georgescu — Fri, 28 Mar 2025 21:09:05 GMT

Hi Achim,

Indeed there is a blacklist on the SIM. The question 2 is about how to reset the saved blacklisted operator on the sim.

By reboot i mean from the code, we do a division by zero so it reboots. Modem factory reset doesn't sound like something the device could do on it's own and we cannot do something like this as a manual maintenance from time to time every few months.

Thanks

RE: Long disconnects with empty PDP on nrf9160

nicolae.georgescu — Fri, 28 Mar 2025 21:06:27 GMT

Hello Øyvind,

Thanks for the fast response!
Unfortunately we don't have a device log for when this problem happens :(. It started happening recently, in Bucharest Romania and also in another two cities.It doesn't seem to happen in Barcelona.

We used to be locked on band 3 that worked well, and in >1 year we only experienced short disconnects that were fixed by either soft retries or rebooting the device.
Couple of months ago the operator started removing band 3 and adding band 20. When we removed band locking the device can connect to other operators (Vodafone besides Orange).
We are not sure multiple operators is the blame, but it is the only significant change that happened.

Modem fw: 2.6.1

Yes, using LTE-M.

Thanks,
Geo

RE: Long disconnects with empty PDP on nrf9160

Øyvind — Fri, 28 Mar 2025 15:23:16 GMT

Hello Geo,

Do you have any application logs that you can share with us, showing what is going on in the device? Is this happening at a specific location, or the whole network? Where have you tested?

What modem FW are you running on your device? Are you also able to collect modem trace?

I will forward this internally to discuss with our network specialists.

[quote user=""]The device intermittently worked on both Vodafone and Orange networks[/quote]

From this information I'm assuming that you are using LTE-M? As these both provide support for LTE-M according to the GSMA Mobile IoT Deployment Map.

Kind regards,
Øyvind

RE: Long disconnects with empty PDP on nrf9160

Achim Kraus — Fri, 28 Mar 2025 07:08:45 GMT

[quote userid="109160" url="~/f/nordic-q-a/120262/long-disconnects-with-empty-pdp-on-nrf9160"]1NCE suggested we could blacklist an operator at their level,[/quote]

There is also a blacklist (forbidden PLMN list) on the SIM. The nasty point will be, if you have two operators and you blacklist one, then an outage of the other (not blacklisted) will disconnect device.

[quote userid="109160" url="~/f/nordic-q-a/120262/long-disconnects-with-empty-pdp-on-nrf9160"]We still see some disconnects of >2 hours even though the device retries (from soft retry to reboot) every ~5 minutes.[/quote]

Not sure, did you also try a modem factory reset before reboot? (Will only help, if your application always initialize the modem proper in restart.)