Environment
Device: applicable to all
SIM type: applicable to all
Question
How often do I need to clear FPLMN?
Can you advise on how can we implement automatic FPLMN clearing logic?
Answer
It depends on the use case.
A few general guidelines are:
FPLMN should not be cleared if network is working as expected.
FPLMN should be cleared when all available networks are on the FPLMN list.
FPLMN should be cleared when none of the networks not on the FPLMN list allows the device to register.
FPLMN should not be cleared excessively / too often, for multiple reasons.
Common logic scenarios include:
Clearing FPLMN after X number of unsuccessful registration attempts;
Clearing FPLMN upon device reboot;
Introducing a sleep mode in between attempts to preserve battery life.
Consult your hardware manufacturer for further guidance.
If you would like to learn how to clear FPLMN list, see this article:
Cause
Concerns related to interrupted connections
Clearing the FPLMN list wipes the record of previously failed networks. If the device later experiences a temporary issue (e.g., weak signal), it may attempt to reselect or re-register with one of those previously failed networks. Without the FPLMN acting as filter in place, the modem will no longer avoid these "bad" networks and might waste time and energy retrying them, resulting in:
Longer time-to-connect during future registration attempts;
Increased risk of temporary service loss, especially in marginal coverage zones.
Concerns related to power consumption
Clearing the FPLMN list too frequently can increase power consumption, especially in low-power or battery-operated devices. Each clear operation may trigger network re-selection and scanning, causing the modem to use its power resources more often than necessary. This not only consumes extra energy but may also interfere with the device’s ability to remain in low-power idle or sleep states, ultimately reducing battery life and operational efficiency.
Concerns related to SIM's flash memory wear*
The FPLMN list is stored in non-volatile memory on the SIM card, typically flash or EEPROM, which has a limited number of write/erase cycles. Each time the FPLMN list is updated or cleared, it results in a write/erase operation to this memory. Repeatedly clearing the FPLMN list, especially when it’s unnecessary (e.g., when already empty), can cause premature wear to the memory cells storing this file. Over time, this can lead to SIM corruption or failure, particularly in environments where devices reset or retry network connections often.
Our UICC SIMs follow ETSI standards and can sustain 20 million updates of highly stressed data throughout their lifetime, so keep this in mind when designing FPLMN-clearing logic.
* This does not apply to SoftSIM.