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Roaming SIM, modem configuration and network attachement

Kevin Barron

We have purchased a radio fitted with the nRF9160 modem and fitted it with a roaming SIM for NB-IoT use, we are in UK and have Band 20 EE and Vodafone.

What are the initial radio AT commands used to select the MNO 

How is network selection determined?

In the event of a loss of an MNO. What thresholds are used to move the SIM to the 2nd MNO?

When a MNO is selected, on a power cycle, is that the 1st MNO checked therefore the radio should go back to previous MNO or does it rescan ?

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  • 0

    Hi,

    Thanks for reaching out to us. Here are our response to your questions:

    1. There is a +COPS command that can be set to select mobile network automatically or manually as mentioned here.

    2. Network selection is governed by standard 3GPP rules (defined in 3GPP TS 23.122) as well as parameters configured on your SIM card. First modem try to attach to the last successfully registered PLMN and there are Preferred PLMN list as well like home PLMN, user-controlled and operator controlled preferred list which can effect the network selection during automatic procedure. For a roaming SIM, the operator controlled list is typically the key list, as it defines which visited networks (e.g. EE, Vodafone) are permitted and their priority. This list is programmed by the SIM provider.

    3. I am not aware of specific exact signal thresholds (such as specific dBm levels for RSRP/RSRQ) that trigger an automatic switch from a lost MNO to a secondary roaming partner MNO (Can you tell exactly which thresholds are you referring, I can try to ask internally if needed). In general, in automatic mode, the modem will attempt to re-establish a connection with the lost network. If the connection fails permanently, the modem will perform periodic cell searches to find alternative available networks listed in your roaming SIM's profile. Whereas in manual mode, the modem will not automatically switch networks upon loss of service unless your application implements its own out-of-service recovery logic to release the lock.

    4. Yes, upon a normal wakeup (such as from PSM) or power-up, the modem's priority is to avoid a full scan to optimize power. So it attempts to find and reconnect to the network that was serving the device before it went to sleep or was powered down.

    Best Regards,
    Syed Maysum

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  • 0

    Hi,

    Thanks for reaching out to us. Here are our response to your questions:

    1. There is a +COPS command that can be set to select mobile network automatically or manually as mentioned here.

    2. Network selection is governed by standard 3GPP rules (defined in 3GPP TS 23.122) as well as parameters configured on your SIM card. First modem try to attach to the last successfully registered PLMN and there are Preferred PLMN list as well like home PLMN, user-controlled and operator controlled preferred list which can effect the network selection during automatic procedure. For a roaming SIM, the operator controlled list is typically the key list, as it defines which visited networks (e.g. EE, Vodafone) are permitted and their priority. This list is programmed by the SIM provider.

    3. I am not aware of specific exact signal thresholds (such as specific dBm levels for RSRP/RSRQ) that trigger an automatic switch from a lost MNO to a secondary roaming partner MNO (Can you tell exactly which thresholds are you referring, I can try to ask internally if needed). In general, in automatic mode, the modem will attempt to re-establish a connection with the lost network. If the connection fails permanently, the modem will perform periodic cell searches to find alternative available networks listed in your roaming SIM's profile. Whereas in manual mode, the modem will not automatically switch networks upon loss of service unless your application implements its own out-of-service recovery logic to release the lock.

    4. Yes, upon a normal wakeup (such as from PSM) or power-up, the modem's priority is to avoid a full scan to optimize power. So it attempts to find and reconnect to the network that was serving the device before it went to sleep or was powered down.

    Best Regards,
    Syed Maysum

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