nrf9151 and nrf9160 PLMN selection criteria

[thomasGronroos]

Hey,

I was trying to look for information on how nrf9160 modem selects the network to use, since we are having slight trouble with some devices triggering full network re-selection when operating at the edge of multiple networks.

So on nrf9151 and nrf9160 what are the PLMN selection criteria when waking up from PSM and what are the requirements for the modem to trigger new attach to a different PLMN when multiple are available?

Also is there a way to steer/prioritize the modem to connect to a specific PLMN but not fully lock it?

[Samruddhi Jadhav]

Hello,

Apologies for the delay in response. I have discussed this with the team and this is their feedback.

After the modem wakes up, it does not change to using another PLMN easily as its goal is to find the network which was serving the device before. So, PSM wakeup doesn't result in an attempt to search networks with higher priority. It will connect to the same previous network which is less power consuming. 

what are the requirements for the modem to trigger new attach to a different PLMN when multiple are available?

There are many factors which could result in attach attempts to other networks such as equivalent PLMNs concept and different methods for home operator (SIM provider) can direct modem to another network via SIM USAT functionality. 

Also is there a way to steer/prioritize the modem to connect to a specific PLMN but not fully lock it?

Manual PLMN selection by the application is the only way to lock device to network and in order to switch networks or to automatic network selection mode, out-of-service logic is needed and would be implemented by the application. Note that this will not prevent moving to those equivalent PLMNs.

Do you have any log files which we could have a look at?

Best Regards,

Samruddhi