How it Works
This section describes how this feature works.
The AMF initiates the Configuration Update Command procedure when it observes a change in the configuration that was previously sent to a UE. Depending on the nature of the configuration that is modified, the AMF communicates with the UE to send an acknowledgment indicating that the configuration has changed or request the UE to register with AMF again.
The AMF checks for the configuration changes and starts the Configuration Update Command after the following procedures are completed:
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PDU establishment
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Xn-based handover
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N2 handover without the AMF change
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UE-initiated service request in the IDLE state without ICSR or without PDU.
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UE-initiated service request in the IDLE state with ICSR.
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Data change notifications from UDM
Timers
The AMF uses timers to detect configuration changes for UEs in the IDLE mode and UEs in the CONNECTED mode without any signaling activity. If AMF detects changes in configuration for UE in the IDLE mode, the UE is paged. Based on the response, the AMF sends the Configuration Update Command.
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T3555—The AMF transmits the Configuration Update Command message with an acknowledgment request to the UE. While waiting for a response from the UE, AMF starts the T3555 timer. If the timer expires, the AMF retransmits the Configuration Update Command message.
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T3512—When the UE moves to the IDLE mode, the AMF starts an internal timer which is derived from T3512 timer value subtracted by 4 minutes. The resulting value must be greater than 60 seconds. When the timer expires, the AMF checks for any configuration changes and triggers Paging if required.
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Tidle—The tidle timer allows AMF to monitor the UE in the CONNECTED mode without any signaling activity for a defined period. On the expiry of this timer, the AMF performs one of the following actions:
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If the configuration is modified and the feature is enabled, the AMF initiates the UE Configuration Update Command and restarts the tidle timer.
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If the configuration has not changed or the feature is disabled, the AMF moves the UE to the IDLE state by sending the respective messages towards gNB and SMF.
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