HPPLMN search - reason unknown

[Achim Kraus]

I was able to perform an test run for the HPPLMN search topic.

See hpplmn search - please consolidate advice.

The capture shows:

nRF9160 SICA B1A
mfw v1.3.3
NB-IoT, PSM: PTAU 24h, Act 4s
SIM-Card: HPPLMN 26201 interval: 2h
Message exchanges every 30min.

PLMN: "26201","D325",9,8,"01CC2B0C"  

(times are times in Wireshark)

1. Exchange
RRC Released 21s, Sleeping 25s => after 4s, no HPPLMN search
 
2. Exchange
RRC Released 1826s, Sleeping 1972s => after 146s, HPPLMN search!

3. Exchange
RRC Released 3626s, Sleeping 3630s => after 4s, no HPPLMN search

4. Exchange
RRC Released 5426s, Sleeping 5430s => after 4s, no HPPLMN search

5. Exchange
RRC Released 7225s, Sleeping 7229s => after 4s, no HPPLMN search

6. Exchange
RRC Released 9026s, Sleeping 9030s => after 4s, no HPPLMN search

7. Exchange
RRC Released 10825s, Sleeping 10964s => after 139s, HPPLMN search!

Please analyze, why the modem starts these HPPLMN searchs.

My understanding is, it is always the PLMN 26201, which is the configured HPPLMN. I don't see the reason, why the searches are executed.

trace-2022-12-16T10-27-46.715Z.zip

[Charlie]

Hi Achim,

Please analyze, why the modem starts these HPPLMN searches.

My understanding is, it is always the PLMN 26201, which is the configured HPPLMN. I don't see the reason, why the searches are executed.

26201 is not the highest priority network. The highest priority network is home network which is 90140. That is why the HPPLMN search must be done and cannot be skipped. Btw, HPLMN seems to have a global PLMN ID (starts with 9). According to 3GPP HPPLMN can only be a PLMN that is in the same country the device currently is located. But because the HPLMN is a global PLMN, it must be searched not matter where the device is located at because such network could be found anywhere. In this log HPLMN 90140 was never found.

Best regards,

Charlie

[Achim Kraus]

Thanks, I will forward that to the MVNO.

[Achim Kraus]

Is that "home network" configured on the SIM-card? How could that be read?

Edit: I think, it's the IMSI header.

[Achim Kraus]

Let me close this issue. That's beyond a user's possibility.

I'm not sure, if the modem will ever find such a global PLMN.

That's a question left to 3GPP or the MVNOs. 

[Achim Kraus]

With mfw 1.3.5, the modem will not longer search for the 90140.

See mfw_nrf9160_1.3.5_release_notes.txt:

- Fix for higher priority PLMN search. Global PLMN IDs (start with digit 9) are no more
  automatically considered to be suitable for higher priority PLMN search and selection.