UE SNPN Reject List Handling for Congestion-Free Network Return

The UE stores SNPN IDs in a 'permanently forbidden SNPNs for access for localized services' list when receiving registration reject messages with cause values indicating permanent unauthorized access. This preliminary action allows the UE to automatically exclude these SNPNs from future registration attempts, reducing congestion in the home network without requiring complex real-time decision-making procedures during network return transitions.

The patent extracts the SNPN ID information from the registration reject message and stores it separately in a dedicated list structure ('permanently forbidden SNPNs for access for localized services'). This extraction approach simplifies the management complexity by isolating the forbidden SNPN list from the main registration processing logic, while maintaining reliable access control through clear separation of concerns.

The patent implements timer-based procedures where the UE monitors the expiration of timers (e.g., Tsor-cm timer) to determine when to transition from NPN to home network. The timer provides feedback on the elapsed time since the last registration attempt, enabling precise timing control for network return transitions while maintaining manageable procedure complexity through standardized timer expiration checks.