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How does SIM configuration interact with device connection logic?

SIM settings and device firmware work together to determine connection behavior and performance.

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Written by Laurent Wijgergangs
Updated over a week ago

Environment

  • Device: applicable to all

  • SIM type: applicable to all

  • Cellular technology: applicable to all

Question

  • What role does SIM configuration play in network connection?

  • How does a device’s firmware influence connection behavior?

  • Why does configuration alignment between SIM and device matter?

  • What is the connection logic and do I have access to this?

Answer

The device firmware contains the connection logic, which in turn references and controls information stored on the SIM. The SIM functions as a sort of 'phone book' for the device.

  • The firmware / connection logic determines:

    • how the device uses SIM data;

    • network scan strategy, retry behavior, and fallback rules;

    • PLMN and RAT preferences;

    • etc.

  • The SIM holds:

    • subscriber information (ICCID, IMSI, MSISDN, etc.);

    • authentication keys;

    • PLMN preference lists (if any)*.
      ​

To learn more about your device’s connection logic, please refer to your device manufacturer’s documentation.

* Onomondo SIMs are non-steered, and do not come with network preference lists. Learn more in this article:

Cause

Generally speaking, it is the device (radiomodule / modem / smartphone) that controls the connection process.

If the SIM allows connections to many networks but the device scans blindly without prioritization, network attachment can take a long time. For optimal performance:

  • Configure the device to align with the SIM’s capabilities and network preferences.

  • Limit the scan scope or apply smart retry rules.

  • Retain previous successful connections where possible to speed up reconnection.

Best practices are detailed further in our IoT Code of Conduct.

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