Unable to receive SMS without forcing network activity on roaming SIM card

Hi,

We are developing an application that should receive commands via SMS. The device runs on a fairly large and rechargeable battery so the power consumption is not the most important.

The SMS receive and send works fine but I have noticed that we only receive SMS after forcing some other network activity such as pushing or pulling IP data. I need the device to wake up on SMS reception.

I use the SMS subscriber library in the modem libraries.

In the simplest of use cases I just call sms_init() followed by sms_register_listener() with a callback function. In this setup I don't receive any SMS. If I then combine this with some code that forces IP data such as code from the udp_with_psm sample I receive the SMS after the UDP NTP activity.

I don't have PSM or eDRX enabled. How can I make sure that I receive SMS when roaming and what latency should I expect (without pushing data I have waited for more than one hour without receiving the SMS ...) ?

I am running a nRF9160 (nRF9160-SICA, BAA-E2.1.8, 11SXH) on a custom board, SW is based on SDK v1.3.0 with modem Firmware 1.2.1. We are running with eSIM and it registers as roaming.

I have logged the following AT commands to verify that PSM and eDRX isn't enabled and to get some information from the network:

CEDRXS:
CEDRXRDP: +CEDRXRDP: 0
CPSMS: +CPSMS: 0
XEPCO: %XEPCO: 1
XDATAPRFL: %XDATAPRFL: 2
XMONITOR: %XMONITOR: 5,"","","24202","09D2",7,20,"01FF5820",485,6300,39,34,"","11100000","11100000","01001001"

The same scenario works fine when not roaming (normal SIM card, not eSIM) and SMS is received instantaneously but the device will have to support roaming and receiving SMS.

Please let me know if you need any further information.

    Best regards,
    
    Daniel.

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