UE Congestion Control Across PLMN Changes Using Back-Off Timers
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Solution Overview
Problem
In the 5G System (5GS), there is ambiguity regarding the continuation of congestion control when a User Equipment (UE) changes from a home Public Land Mobile Network (PLMN) to a destination PLMN, leading to unclear management of control signals.
Innovation Solution
The UE implements a mechanism where it receives a Protocol Data Unit (PDU) session establishment reject message with a back-off timer value and specific Single Network Slice Selection Assistance Information (S-NSSAI), and based on this, it postpones any further PDU session establishment or modification requests until the timer expires, ensuring consistent congestion control across PLMNs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the UE continues congestion control when changing from home PLMN to destination PLMN, then network resource allocation is improved, but device complexity increases due to unclear control signal management
Solution Approach 1:
The network side performs preliminary action by including congestion control indication information in the PDU session establishment reject message before the UE changes PLMN. This allows the UE to pre-configure the back-off timer and congestion control parameters, ensuring continuous congestion control when moving to destination PLMN without requiring complex real-time decision-making at the UE side.
Solution Approach 2:
The congestion control indication information and back-off timer value act as intermediaries between the network side and UE. These parameters carry the network's congestion control intentions across PLMN boundaries, simplifying UE behavior by providing clear, pre-defined instructions rather than requiring the UE to manage complex control signals autonomously.
2Speed
If the UE sends PDU session establishment requests during network transition, then communication speed is improved, but network resource allocation deteriorates due to unnecessary requests
Solution Approach 1:
The network side performs preliminary anti-action by sending congestion control indication information and starting a back-off timer in the PDU session establishment reject message before the UE initiates new session requests. This pre-prevents the UE from sending unnecessary PDU session establishment or modification requests during the back-off period, reducing network resource consumption while maintaining clear communication protocols.
3Reliability
If the back-off timer is applied to every PLMN, then congestion control reliability is improved, but device complexity increases
Solution Approach 1:
The back-off timer mechanism is designed with universality to function across multiple PLMNs. The congestion control indication information and back-off timer values are configured to apply to every PLMN or registered PLMN as indicated by the network, allowing the same timer management mechanism to serve multiple networks without requiring separate timer configurations for each PLMN, thus reducing device complexity while maintaining broad applicability.
Data Source
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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.