UE Back-Off Timer for PLMN Change Congestion Control
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Solution Overview
Problem
In the 5G mobile communication system, it is unclear whether congestion control is maintained when a User Equipment (UE) changes its Public Land Mobile Network (PLMN), specifically regarding resource availability for specific network slices and Data Network Names (DNNs), leading to inefficiencies in control signal management during system changes.
Innovation Solution
A UE implementation that receives a Protocol Data Unit (PDU) session establishment reject message starts a back-off timer when resource insufficiency is indicated for a specific slice and DNN, and temporarily halts subsequent PDU session establishment or modification requests across all PLMNs until the timer expires, ensuring consistent congestion control management.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the UE continues PDU session establishment requests after receiving resource insufficiency indication in home PLMN, then the UE can attempt to establish sessions in destination PLMN, but this causes resource overload and ineffective congestion control
Solution Approach 1:
The patent applies preliminary anti-action by implementing congestion control mechanisms before the UE can cause resource overload in the destination PLMN. When the home PLMN sends a PDU session establishment reject message with resource insufficiency indication, the UE proactively prevents further session establishment requests across all PLMNs by starting a back-off timer, thereby avoiding the harmful effect of resource overload before it occurs.
Solution Approach 2:
The patent uses the back-off timer as an intermediary mechanism to mediate between the UE's need to establish sessions and the network's resource constraints. The timer acts as a controlled delay that prevents immediate re-attempts, allowing the network to recover resources while providing a structured approach to congestion control that balances session establishment needs with resource availability.
2Device complexity
If the UE implements congestion control in home PLMN only, then the control mechanism is simple to implement, but the congestion control is not maintained when changing to destination PLMN
Solution Approach 1:
The patent applies universality by making the congestion control mechanism applicable across multiple PLMNs rather than being limited to the home PLMN. The back-off timer mechanism established in response to home PLMN resource insufficiency indications automatically extends to prevent session establishment requests in destination PLMNs as well, providing universal congestion control that maintains reliability during PLMN changes without requiring separate control mechanisms for each PLMN.
3Speed
If the UE immediately re-attempts PDU session establishment after reject message, then the response time is fast, but this leads to repeated resource requests and ineffective congestion management
Solution Approach 1:
The patent implements periodic action by using the back-off timer to create controlled intervals between session establishment attempts. Instead of immediate continuous re-attempts, the UE waits for the timer to expire before attempting new sessions, providing a periodic rhythm to congestion control that reduces wasted re-attempt time while maintaining the capability for relatively quick session establishment when resources become available.
Data Source
AI summary
According to one aspect of the present invention, a communication control method is provided that determines whether congestion control is to be continued in a destination PLMN in a case that a PLMN is changed during the application of congestion control and the PLMN before the change is a home PLMN. In a case that the PLMN is changed while a back-off timer received along with a cause value for the congestion control is running and the PLMN before the change is a home PLMN, it is determined whether to allow UE to transmit an SM request message in the destination, based on the presence or absence of an information element notified from the network.