Multi-IMSI connectivity issues

RE: Multi-IMSI connectivity issues

Hakon — Mon, 27 Apr 2026 09:13:59 GMT

[quote user="0sleep"]

This leads me to another question: When I move far enough away from all cells, I get disconnected due to being out of range. The network module handles LTE_LC_EVNT_PDN_DEACTIVATED, LTE_LC_EVT_PDN_NETWORK_DETACH and LTE_LC_EVT_PDN_SUSPENDED events as a "network disconnect" event, but sometimes the device is out of cell range and does not receive these events. In this case, checking CEREG shows NETWORK_REG_UNKNOWN (code 4).

Is it the right thing to then also treat LTE_LC_NW_REG_UNKNOWN as a NETWORK_DISCONNECTED event (and then call lte_lc_connect_async), or will lte_lc's PDN module eventually emit a PDN_NETWORK_DETACH event?

[/quote]

If you have any further questions not directly related to your original inquiry, please open a separate ticket for that. Thanks.

RE: Multi-IMSI connectivity issues

BrandonNMiller — Mon, 27 Apr 2026 07:47:16 GMT

@war the knights Thank you for sharing! I agree in your post!

RE: Multi-IMSI connectivity issues

0sleep — Sun, 26 Apr 2026 11:50:55 GMT

I have had a poke around, and noticed that all "non-working" devices had switched to NB-IOT, while the working devices are on LTE-M. After a quick search, this makes complete sense. NB-IOT supports UDP only, which is fundamentally incompatible with MQTT (which needs TCP), oops. Setting CONFIG_LTE_LC_SYSTEM_MODE_LTE_M_GPS=y instead of the default CONFIG_LTE_LC_SYSTEM_MODE_LTE_M_NBIOT_GPS=y used in the asset tracker template ensures LTE-M only.

RE: Multi-IMSI connectivity issues

Achim Kraus — Wed, 15 Apr 2026 11:41:46 GMT

Let me recommend, that you first ask your SIM provider, how the SIM switches between the IMSIs.

Auto switching with timeout? Then it will be contra-productive to switch off the modem, because the SIM may stay at a IMSI, which has no subscription for the available networks.

And short timeout (e.g. 3 mins) make it less possible to search for both NB-IoT and LTE-M networks, so also that value should be know.

Explicitly switching by "AT+CRSM" or similar? Then your issue may be not really related to the SIM. There are a couple of network search optimization implemented in the modem, e.g. "sticky rejection codes", which may help in some cases and other cases you will need to restart the modem with CFUN=0 and CFUN=1. And if that doesn't work, reboot the device.

RE: Multi-IMSI connectivity issues

Hakon — Tue, 14 Apr 2026 12:34:46 GMT

Hello,

[quote user=""]How do I diagnose it[/quote]

A good start would be to capture a modem trace.