Meaning
Non-volatile network rejection codes are returned by a cellular base station to indicate that the requested public land mobile network is not authorized for the subscriber. Receipt of cause 11 PLMN not allowed forces the cellular modem to add the targeted network operator to its forbidden list and immediately stop further registration attempts. This code remains active until the user manually changes the SIM or a timer expires, preventing continuous, unauthorized attachment loops.
Modem Action
Wireless modules must respond to this code by writing the rejected carrier identity directly into the subscriber identity module. The module will not scan for or attempt to connect to this specific operator during subsequent boot cycles. Hardware integration must handle this state to prevent the device from becoming permanently offline in areas with limited carrier options.
Software Recovery
Software drivers implemented on the host microcontroller can monitor these events through unsolicited response codes. If a device receives this rejection, the application logic should switch to an alternative SIM slot or initiate a reset of the cellular configuration. This proactive management prevents remote assets from being permanently stranded on an invalid network.
Field Performance
Deploying smart meters across multiple countries requires careful management of these forbidden lists during initial commissioning. Telemetry applications that fail to catch these codes can waste energy by scanning for unauthorized signals. Implementing a clearing mechanism for the forbidden list ensures that units can recover when network access is restored.
