Guard Timer for NAS Signaling Connection Release in PLMN Selection
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Solution Overview
Problem
In wireless mobile communication networks, UE (User Equipment) faces challenges in performing PLMN (Public Land Mobile Network) selection after a de-registration or detach procedure due to unresolved NAS signaling connections, particularly when the network fails to release the connection and the guard timer is not started, preventing the UE from entering idle mode for network selection.
Innovation Solution
The UE initiates a guard timer upon completion of a de-registration or detach procedure, locally releasing NAS signaling connections upon timer expiry to ensure it can enter idle mode and perform PLMN selection, thereby allowing network selection by starting a guard timer upon receiving a de-registration or detach accept message.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the network fails to release the NAS signaling connection after de-registration or detach procedure, then the connection remains active in the network, but the UE cannot enter idle mode to perform PLMN selection
Solution Approach 1:
The patent applies preliminary action by having the UE start a guard timer before actually releasing the NAS signaling connection. This timer is started in advance upon receiving the de-registration accept or detach accept message, allowing the UE to proactively prepare for connection release and subsequently enter idle mode for PLMN selection, even if the network fails to release the connection.
Solution Approach 2:
The patent implements feedback through the guard timer mechanism that monitors whether the network has released the NAS signaling connection. The timer provides feedback about the connection state, and upon expiry without receiving a release command, the UE autonomously releases the connection and transitions to idle mode, ensuring PLMN selection capability is restored.
2Adaptability or versatility
If the guard timer is not started after de-registration or detach procedure, then the UE maintains connection state, but the UE cannot perform PLMN selection requiring idle mode
Solution Approach 1:
The patent applies preliminary action by mandating that the UE starts the guard timer as part of the de-registration or detach procedure completion. This timer is started in advance to ensure the UE can subsequently enter idle mode for PLMN selection, making the system adaptable to network selection requirements while managing complexity through standardized timer initiation.
3Ease of operation
If the UE locally releases the NAS signaling connection upon guard timer expiry, then the UE can enter idle mode for PLMN selection, but the connection may be released before network confirmation
Solution Approach 1:
The patent applies beforehand cushioning by introducing a guard timer that provides a time buffer between the de-registration/detach procedure completion and the actual NAS signaling connection release. This timer cushioning allows the network adequate time to release the connection before the UE does so locally, preventing premature release while ensuring the UE can eventually enter idle mode for PLMN selection if the network fails to release the connection.
Data Source
AI summary
A method of NAS signaling connection handling when a UE initiates a de-registration or detach procedure to perform network selection is proposed. To allow the UE to perform PLMN selection, the UE needs to be in idle mode. Upon the completion of a UE-initiated de-registration or detach procedure, the UE starts a guard timer, e.g., T3540/T3440. In one example, the UE starts a guard timer upon receiving a de-registration accept message. In another example, the UE starts a guard timer upon receiving a detach accept message. The UE will locally release any NAS signaling connection upon the guard timer expiry so that the UE can enter idle mode and perform PLMN selection.