Section: 4.8.2.2b Network Triggered Connection Resume in RRC_INACTIVE with CN based MT communication handling
Content: When the UE is in CM-CONNECTED with RRC_INACTIVE state with CN based mobile terminating (MT) communication handling, high latency communication as described in clause 5.31.8 of TS 23.501[ System architecture for the 5G System (5GS) ]  [2] is applied. This procedure may be triggered by MT data, or a N1 procedure from SMF and UPF as shown in Figure 4.8.2.2b-1. When the procedure is triggered by other NFs (e.g. SMSF, LMF, GMLC), the UPF (or SMF) in the following figure should be replaced by the respective NF (the corresponding service operations used by other NFs when they communicate with AMF may also be different from the service operations used by SMF/UPF). For MT-SMS delivery request from SMSF, see also procedures defined in clause 4.13.3.6, clause 4.13.3.7 and clause 4.13.3.8. During the procedure, the NG-RAN (i.e. gNB) performs RAN paging towards the UE based on the N2 message from the AMF in order to trigger the UE triggered Connection Resume procedure in clause 4.8.2.2. Figure 4.8.2.2b-1: Network Triggered Connection Resume for UE in RRC_INACTIVE with CN based MT communication handling 1a. When downlink data is received and the SMF/UPF is requested to perform buffering as specified in clause 4.8.1.1a, the UPF/SMF checks with AMF for the possibility of data delivery, similar to step 2 of clause 4.24.2 with the following differences: - The UPF provides the DL data size information of the QoS Flow when sending Data Notification to SMF if the UPF has received instruction from SMF. - In the Namf_MT_EnableUEReachability the SMF may also send the following parameters the PPI, the ARP and the 5QI, DL data size and/or QFI for the QoS Flow of the PDU Session which triggered the request for paging policy differentiation as defined in clause 5.4.3.2 of TS 23.501[ System architecture for the 5G System (5GS) ]  [2]. If the SMF, while waiting for UE triggered Connection Resume indication or a reject response (with Estimated Maximum Wait time) from the AMF, receives any additional Data Notification message due to additional data packets for another QoS Flow associated with a higher priority (i.e. ARP priority level) than the priority indicated to the AMF in the previous Namf_MT_EnableUEReachability, or the SMF derive a different Paging Policy Indicator according to the additional Data Notification, the SMF invokes a new Namf_MT_EnableUEReachability indicating the higher priority or different Paging Policy Indicator to the AMF. The information contained in the new Namf_MT_EnableUEReachability request overrides the information from the previous Namf_MT_EnableUEReachability request that is stored in the AMF. If the SMF receives any additional Data Notification messages due to additional data packets for another QoS Flow associated with same or lower priority than the priority indicated to the AMF in the previous Namf_MT_EnableUEReachability or if the SMF has sent the second Namf_MT_EnableUEReachability message indicating the higher priority and receives additional downlink data packets for this UE, based on local configuration, the SMF either buffers these Data Notification messages and does not send a new Namf_MT_EnableUEReachability message, or the SMF sends a new Namf_MT_EnableUEReachability message to AMF. - The AMF determines if the UE is reachable based on the stored eDRX values for RRC_INACTIVE state provided by NG-RAN in clause 4.8.1.1a. If the UE is unreachable, the AMF stores the information received in the Namf_MT_EnableUEReachability request and provides the Estimated Maximum Wait time in the response message based on the eDRX values for RRC_INACTIVE in AMF (steps 2-5 are postponed until the UE becomes reachable). If the UE is considered reachable, step 2 is executed immediately. NOTE 1: This handling is similar to CM-IDLE with eDRX. When the AMF provides the Estimated Maximum Wait time, it can consider the time needed for RRC level procedures (e.g. RRC RNA update procedure) when UE wakes up from the eDRX cycle. NOTE 2: The other NFs can use the Namf_Communication_N1N2MessageTransfer service operation to deliver the MT signalling. 2. When the AMF determines that the UE is reachable, the AMF sends a RAN Paging Request message to NG-RAN with the request for the UE's RRC connection to be resumed. The AMF may include the following per QoS Flow parameter(s) the PPI, the ARP and the 5QI, DL data size and/or QFI for the QoS Flow(s) of the PDU Session in the RAN Paging Request message to trigger and enable RAN paging. If the AMF receives MT signalling (i.e. via Namf_Communication_N1N2MessageTransfer) in step 1a, AMF includes DL Signalling indication in the N2 RAN Paging Request message. 3. NG-RAN performs RAN paging towards the UE considering the parameters provided by the AMF. Based on the DL data size for QoS Flow(s), if it's provided, the NG-RAN determines whether to set the MT-SDT flag as defined in TS 38.300[ NR; NR and NG-RAN Overall description; Stage-2 ]  [9]). 4. When the UE receives RAN paging, it initiates the UE triggered Connection Resume procedure and NG-RAN notifies CN as specified in clause 4.8.2.2 including the N2 Notification in step 3b. 5. The UPF triggers downlink data delivery if there is any. The AMF sends downlink NAS messages if there is any.