Section: 4.8.3 N2 Notification procedure
Content: This procedure is used by an AMF to request the NG-RAN to report RRC state information, when the target UE is in CM-CONNECTED state. When AMF has requested reporting of subsequent state changes, the need for the NG-RAN to continue reporting ceases when the UE transitions to CM-IDLE or the AMF sends a cancel indication. This procedure may be used for services that require RRC state information (e.g. 5GC MT control and paging assistance, O&M and collection of statistics), or for subscription to the service by other NFs. See TS 38.413[ NG-RAN; NG Application Protocol (NGAP) ]  [10] for details of the procedure. Reporting of RRC state transitions can be requested per UE by AMF. Continuous reporting of all RRC state transitions can be enabled by operator local configuration. Figure 4.8.3-1: RRC state transition notification 1. The AMF sends a UE State Transition Notification Request to the NG-RAN as described in TS 38.413[ NG-RAN; NG Application Protocol (NGAP) ]  [10]. The UE State Transition Notification Request message shall identify the UE for which notification(s) are requested and may contain a reporting type. The reporting type either indicates subsequent state transitions shall be notified at every RRC state transition (i.e. from RRC_CONNECTED state to RRC_INACTIVE state, or from RRC_INACTIVE to RRC_CONNECTED state), or it indicates Single RRC_CONNECTED state notification. 2. The NG-RAN sends the UE Notification message to report the current RRC state for the UE (i.e. RRC_INACTIVE state or RRC_CONNECTED state). The current UE location information (i.e. TAI + Cell Identity) is always included when RRC state information is reported. 2b. When the AMF has requested reporting about subsequent state transitions, the NG-RAN sends subsequent UE Notification messages to the AMF at every RRC state transition until the UE transitions to CM-IDLE or NG-RAN receives a Cancel UE State Notification message from the AMF. When the AMF has requested reporting for Single RRC_CONNECTED state notification and UE is in RRC_CONNECTED state, the NG-RAN sends one UE Notification message but no subsequent messages. If UE is in RRC_INACTIVE state, the NG-RAN sends one UE Notification message plus one subsequent UE Notification message when RRC state transits to RRC_CONNECTED. 3. The AMF can send a Cancel UE State Notification message to inform the NG-RAN that it should terminate notifications for a given UE. This message should only be used when notification(s) about subsequent state transitions was requested at every RRC state transition.