IoT Device Implementation Guide

Implement device recovery mechanisms

Last Updated: July 3rd, 2024

While suspending or terminating a SIM will have the effect of instructing a network to reject a connection, there are also many other scenarios where a device may not be able to connect to a network, such as temporary cellular network problems.

While rare, some scenarios may further result in the communications module adding the network to the Forbidden PLMN (FPLMN) list β€” a list stored in the SIM that the module uses to determine which networks it should ignore β€” due to being unable to connect.

This can have a significant effect on the IoT device, such as losing connectivity even after a temporary network issue has been resolved.

3GPP Standard Release 10 and above defines a procedure for a communications module to automatically clear the FPLMN list at a specific interval in order to recover from such scenarios. However, modules that only support Release 9 or below might not be able to clear the list automatically, and may therefore be unable to reconnect without manually clearing the FPLMN list or rebooting the device.

Depending on requirements, implementing a suitable recovery mechanism is recommended. For example, if a device has a user-accessible reset button, the IoT Device Application should be designed to actively clear the FPLMN list as part of its reset procedure.

For devices that will operate autonomously, the application should automatically clear the FPLMN list if the device has not been able to connect to a network for a long time (e.g.: 2 days). Note that if a device has completely lost connectivity, remotely triggering a reset procedure would not be possible and, therefore, would not be a suitable recovery mechanism on its own.

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