Temporary Forbidden PLMN List and Timer T3247 Mechanism
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Solution Overview
Problem
Current 3GPP specifications lead to permanent unavailability of Public Land Mobile Networks (PLMNs) when reject messages from fake operators are misinterpreted, causing PLMN IDs to be added to the Forbidden PLMN list without integrity protection, resulting in unnecessary power consumption and delayed service recovery.
Innovation Solution
Introducing a temporary Forbidden PLMN list and a timer (T3247) to prevent immediate addition of PLMN IDs to the permanent list upon reject messages without integrity protection, allowing retries after the timer expires, thus avoiding malicious blocking and enabling network access recovery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the UE adds PLMN ID to the Forbidden PLMN list upon receiving reject messages without integrity protection, then the UE avoids unnecessary registration attempts to fake operators, but the UE experiences permanent blocking and delayed service recovery even when the network becomes available
Solution Approach 1:
The patent segments the Forbidden PLMN list into two distinct parts: a permanent Forbidden PLMN list stored in the SIM/USIM and a temporary extension list stored in the UE's volatile memory. This segmentation allows the UE to maintain permanent blocking for confirmed malicious networks while enabling temporary blocking with auto-expiry for suspicious networks, thus resolving the contradiction between avoiding fake operators and enabling rapid service recovery.
Solution Approach 2:
The patent implements preliminary action by introducing a timer (T3247) that automatically expires after a predetermined duration. This timer is started when a PLMN ID is added to the temporary extension list, and its expiry automatically removes the PLMN ID from the list without requiring user intervention or additional network communication, enabling automatic service recovery.
2Object-affected harmful factors
If the UE maintains a permanent Forbidden PLMN list to block fake operators, then the UE avoids security risks, but the UE consumes unnecessary power and delays service recovery when networks are temporarily unavailable
Solution Approach 1:
The patent segments the blocking mechanism into permanent and temporary components. The permanent Forbidden PLMN list in the SIM/USIM provides ongoing security protection, while the temporary extension list in volatile memory handles suspicious networks with automatic expiry. This reduces power consumption compared to maintaining all blocked networks permanently, as temporary entries are automatically removed after timer expiry.
Solution Approach 2:
The patent uses the temporary extension list as a disposable, short-lived blocking mechanism. Entries in this list are automatically removed after the timer expires, eliminating the need for continuous power consumption to maintain the blocking state. This allows the UE to aggressively block suspicious networks temporarily without the long-term power cost of permanent blocking.
3Reliability
If the UE immediately adds PLMN ID to the Forbidden PLMN list upon reject messages, then the UE prevents repeated registration attempts to malicious networks, but the UE loses network access opportunities when the network issue is temporary
Solution Approach 1:
The patent segments the blocking mechanism into permanent and temporary lists. The permanent list provides reliable blocking for confirmed malicious networks, while the temporary extension list provides flexible, time-limited blocking for suspicious networks. This dual-list approach maintains blocking effectiveness while improving adaptability to temporary network issues.
Solution Approach 2:
The patent introduces dynamic behavior to the blocking mechanism through the timer (T3247). The temporary extension list entries are dynamically added and removed based on timer expiry, allowing the UE to adapt its network access behavior over time. This dynamic approach enables the UE to block suspicious networks initially but automatically recover access if the network becomes available within the timer period.
Data Source
AI summary
A method of enhanced handling of a Forbidden Public Land Mobile Network (PLMN) list is proposed. When a UE tries to attach to a PLMN and receives an ATTACH Reject message having no integrity protection, it could be transmitted from a network entity trying to block the PLMN for providing service. Therefore, by introducing a temporary forbidden PLMN list and a timer T3247, UE can avoid adding the PLMN ID to the Forbidden PLMN list and avoid being blocked for network access. Instead, UE is only temporary refrained from selecting the PLMN ID and is able to retry for the network access after T3247 expiry. The temporary list together with T3247 mechanism thus gives UE more opportunity to try with the same PLMN ID at a different time and/or a different UE location, where the malicious blocking is no longer available.