Notifications using the UE Configuration Update Command
The UE Configuration Update Command is responsible for communicating the modification in the SMS state to the UE. The SMS state, such as allowed and not allowed is modified when the AMF CLI is modified or the AMF receives the subscription change notification through the UDM data change notification.
When the AMF detects changes in the SMS state for a UE, and the UE requested in the previously sent Registration Request for the SMS, the AMF notifies the new SMS state through the UE Configuration Update Command.
If the UE had requested the SMS based on CLI configuration or SMS subscription, the AMF marks the SMS as allowed or not allowed and informs the UE through the Registration Accept message. Later, when the SMS state changes at AMF; for example, the UDM subscriptions change the SMS state from allowed to not allowed. In that case, the UE Configuration Update Command notifies the UE with the SMS IE indication as not allowed.
For the UDM notifications, when the UE is in the CONNECTED state, the UE Configuration Update Command is triggered instantly. However, paging is triggered based on the AMF configuration if the UE is in the IDLE state.
Whenever the SMS state at AMF changes from allowed to not allowed, and if the SMS was previously activated, the AMF sends the Deactivation Request to SMSF.