Forbidden PLMN

Register Maintenance

Cellular modules update non-volatile memory whenever a base station returns location updating rejection codes. Adding an entry to the forbidden plmn list occurs automatically after receiving specific network cause values such as PLMN Not Allowed or Roaming Not Allowed In This Location Area.

Selection Behavior

Automatic network selection algorithms bypass blocked carrier identities during initial cell search procedures. A modem encountering a forbidden plmn checks alternative available frequencies to locate an allowed carrier without transmitting access requests to restricted cell towers. Manual selection attempts by management software bypass this restriction, forcing the terminal to attempt registration despite existing database blocks.

Suppressing futile registration attempts extends battery endurance in remote cellular deployments.

Removal Threshold

Storage boundaries for restricted networks depend on SIM card memory architecture and modem file systems. Clearing a forbidden plmn requires power cycles, manual operator commands or explicit over-the-air updates from the home network manager. Stale rejection entries prevent devices from connecting to newly activated cellular towers.