HPPLMN search - Please consolidate advice.

[Achim Kraus]

Since being aware of the power consumption of the "HPPLMN searchs", I'm struggling to see the right strategy.

What makes me really wondering, is that the first questions are raising already two years ago:

nrf9160 psm and hplmn search on roaming sim cards

unfortunately, the answer is missing there.

3 months ago in lte_lc_nw_reg_searching and lte_lc_modem_evt_search_done the recommendation was to lock the PLMN.

2 weeks ago in measured scanning procedure a few minutes after connection establishment the recommendation was "use only home network".

Using "only home network", really? Isn't the downside of that, that SIM cards of MVNOs are always roaming?

Therefore I would really appreciate, if Nordic spend some more time in investigate, what users should do.

The first question 2 years ago, mentions, that other modems offers to disable the HPPLMN search. Maybe that's considered.

[Charlie]

Hi Achim,

Thanks for summarising the tickets related to the concern of HPPLMN search causing the extra power consumption. After talking with our development and product management teams, I have a summary about the current state of this topic. 

We do not have a plan to disable HPPLMN search at the current time, because it will break the current 3GPP spec.

4.4.3.3.1 Automatic and manual network selection modes  of TS23.122

....

For an MS that only supports any of the following or a combination of EC-GSM-IoT or Category M1 or
Category NB1(as defined in 3GPP TS 36.306 [54]): T is either in the range 2 hours to 240 hours, using 2 hour
steps from 2 hours to 80 hours and 4 hour steps from 84 hours to 240 hours, or it indicates that no periodic
attempts shall be made. If no value for T is stored in the SIM, a default value of 72 hours is used.

....

The attempts to access the HPLMN or an EHPLMN or higher priority PLMN shall be as specified below:

...

d1) periodic attempts may be postponed while the MS is in power saving mode (PSM) (see 3GPP TS 23.682 [27A]).

For the customer/developer, this is a clear power consumption issue, but they are not the only stakeholder in this field. When not in home network (i.e. device is roaming), then it is also in operators interests that the device uses the highest priority network available (based on SIM configuration). This is because depending on the subscription, higher roaming prices may be either operator's or customer's responsibility and the ordering of PLMNs configured to SIM card is typically done based on roaming agreements.

Having this said, there is a exception: If application manually selects the network with AT+COPS, then HPPLMN searches are not done because the selected network could not be changed anyway due to the manual network selection mode. Downside in this approach is that if the manually selected network is not available at some point due to movement of the device, modem will keep searching only the manually selected network even though there would be other suitable networks available. Switching back to automatic network selection mode would help in this situation.

The current solution for this issue is to use the local network or lock the PLMN if you clearly know where the devices will be deployed. Some MVNOs start to support eUICC on their SIM cards, which can select local network profiles for cellular connection instead of roaming.

Best regards,

Charlie

[Achim Kraus]

michal 

Your expert was saying:

"I have consulted my colleagues about it and using the +COPS command is not recommended for that at all."

Is the above advice/recommendation agreed?

[Achim Kraus]

> Automatic and manual network selection modes

> it is also in operators interests that the device uses the highest priority network available (based on SIM configuration).

As long as "manual network selection" is used, the interests of the operators seems to be not that important.

The SIM Card offers at least two lists:

- User controlled PLMN selector with Access Technology '6F60'

- Operator controlled PLMN selector with Access Technology '6F61'

Which one does Nordic support?

What is the priority, when both are used?

Does the modem executes such a search, even if in roaming already the highest priority PLMN is active?

What PLMN encoding does Nordic assume/support in the selector list? e.g. is "62F210" interpreted as "26201"?

Does "%XDATAPRFL" change the interval of the SIM-Card for such a HPPLMN search?

Does "%REDMOB" change the interval of the SIM-Card for such a HPPLMN search?

So, yes, if that function is important, I would welcome, if more details about the implementation gets available. Otherwise, my concern would be, that much more energy is used, than everyone assumes.

[Charlie]

Hi Achim,

The SIM Card offers at least two lists:

• User controlled PLMN selector with Access Technology '6F60'

• Operator controlled PLMN selector with Access Technology '6F61'

Which one does Nordic support? What is the priority, when both are used?

Nordic supports both. User controlled PLMN list has higher priority than the operator controlled PLMN list - as per 3GPP.

Does the modem executes such a search, even if in roaming already the highest priority PLMN is active?

No.

What PLMN encoding does Nordic assume/support in the selector list? e.g. is "62F210" interpreted as "26201"?

Yes it is: MCC2MCC1MNC3MCC3MNC2MNC1. If MNC3 is 'F' it is ignored.

Does "%XDATAPRFL" change the interval of the SIM-Card for such a HPPLMN search?

No. Data profile is proprietary functionality and does not break 3GPP specification.

Does "%REDMOB" change the interval of the SIM-Card for such a HPPLMN search?

No.

Best regards,

Charlie

[Achim Kraus]

Thanks a lot!

That helps me to optimize the behavior.