Support IMSI switch so that nRF9160 board can work in Vietnam

[LuckyMan]

Dear Nordic Team,

I would like to use Nordic nRF9160 DK for NB-IoT applications in Vietnam, and we are using Emnify SIM cards (See also at: https://www.emnify.com/ ) for these NB-IoT applications.
Upon review of these SIMs supported by Emnify, the nRF9160 board which is located in Vietnam uses 29505* IMSI and we cannot use the NB-IoT network in Vietnam now.
I contacted Emnify and they told me that to able the device to connect to the NB-IoT network in Vietnam the device/nRF9160 board must switch to 29509* IMSI, and I should contact you to check if the board supports IMSI switch otherwise NB-IoT connection will not work.

I wonder if our board can switch to 29509* IMSI?

Your support will be appreciated.

Best regards,
Van Vu

[Achim Kraus]

AFAIK, there are two ways to switch the IMSI, if multi-imsi-cards are used.

The "traditional way" works "automatically" with network search timeouts. E.g. depending on the SIM card, the modem tries to register at available networks. But if that is not successful for a certain amount of time, the SIM card switches the IMSI to the next one. In my experience, this timeout start from 2 minutes and may reach 10 minutes.

One pitfall, especially with the "fast switching cards (2 minutes)" maybe that switching the IMSI also interrupts and restarts the network search. Especially in mixed mode (NB-IoT and LTE-M) that may fail to connect to a network at all.

Though such "long network searchs" are also drain the batteries a lot, there are also multi-imsi-cards, which has an API to switch between the IMSIs. You need to ask your SIM card provider about that API. This usually done by using some AT/SIM card command, e.g.

AT+CRSM=220,28616,1,4,13,"0001FFFFFFFFFFFFFFFFFFFFFF"

does it for a SIM card I'm using (it's not an EMnify, I don't think it works with that.

From EMnify - Device configuration guidelines for IMSI Switch handling

_________________________________________________________________________

a) The device must be capable of handling "SET UP EVENT LIST", "POLL INTERVAL" and "REFRESH" proactive commands as specified in 3GPP TS31.111. This is applied when the SIM-card applet modifies the IMSI value.

b) emnify SIMs require a minimum of 128 seconds to perform an IMSI switch after an unsuccessful network-attach attempt (failed location update). As emnify SIMs can have up to three IMSIs per country it is recommended to ensure devices try for a minimum of 300 seconds to perform a network search and a subsequent network attach.

c) Devices must not enter an IDLE state or automatically restart for a minimum of 300 seconds while no network attachment is possible.

____________________________________________________________________________

In my experience, the nRF9160 supports a).

b) with 128s ... that may be too short. Try it, if you see the modem frequently restarting the network search, I guess you need to enable NB-IoT only (without LTE-M). If that results still in restarting network searches, you may need to select bands as well.

c) That's the easy part. Just switch the modem on and don't offline before that 300s.

[LuckyMan]

Dear Achim,

Thank you so much for your support.

Let me double-check it step-by-step and see what the issue is.

Best,

Van Vu

[LuckyMan]

Dear Achim,

My device can access the Cellular Network in Vietnam.

My devices need 15 minutes to be successful in performing a network search. Another possible reason that led to my failure before is the coverage of the network.

Thank you so much for your suggestion.

Best,
Van Vu

[Achim Kraus]

> My device can access the Cellular Network in Vietnam.

Brilliant!

> Thank you so much for your suggestion.

You're welcome.