Section: 4.8.1.1a Connection Inactive procedure with CN based MT communication handling
Content: This procedure may be initiated by the serving NG-RAN node when CN based mobile terminating (MT) communication handling is requested for a UE that is configured with eDRX cycle value longer than 10.24 seconds for RRC_INACTIVE state and has at least one PDU session with active user plane as defined in clause 5.31.7 of TS 23.501[ System architecture for the 5G System (5GS) ]  [2]. Figure 4.8.1.1a-1: NG-RAN initiated Connection Inactive procedure with CN based MT communication handling 0. The UE is registered in the network with negotiated eDRX parameters for CM-IDLE state and is in CM-CONNECTED with RRC_CONNECTED state. The AMF provides the eDRX values for CM-IDLE state to NG-RAN as part of the RRC Inactive Assistance Information as defined in clause 5.3.3.2.5 of TS 23.501[ System architecture for the 5G System (5GS) ]  [2]. 1. NG-RAN determines eDRX values for UE in RRC_INACTIVE state and decides to initiate Connection Inactive with CN based MT communication handling as specified in clause 5.31.7.2.4 of TS 23.501[ System architecture for the 5G System (5GS) ]  [2]. 1a. Optionally the NG-RAN may initiate state transition from RRC_CONNECTED to RRC_INACTIVE with RRC configuring eDRX value as specified in TS 38.300[ NR; NR and NG-RAN Overall description; Stage-2 ]  [9]. The NG-RAN may send the request in step 2 towards CN immediately following step 1a or the NG-RAN may delay this request towards CN as specified in clause 5.31.7.2.1 of TS 23.501[ System architecture for the 5G System (5GS) ]  [2]. 2. Either immediately following step 1a or after having delayed the request for NG-RAN based on implementation, the NG-RAN sends N2 MT Communication Handling request message to AMF indicating the UE is transitioning to RRC_INACTIVE state. The CN takes the NG-RAN request into consideration and handles MT communication. The NG-RAN also provides the determined eDRX values for RRC_INACTIVE to AMF. If the NG-RAN receives DL NAS message and the UE is in RRC_INACTIVE with RRC configured eDRX and is considered not reachable, NG-RAN indicates to the AMF a NAS non-delivery and then initiates for the CN to handle mobile terminated (MT) communication. 3. For each of the PDU sessions with user plane resources have been activated, the AMF invokes Nsmf_PDUSession_UpdateSMContext Request (PDU Session ID, Cause, Operation type, User Location Information, Age of Location Information, N2 SM Information (Secondary RAT usage data), CN based MT handling indication) towards SMF. The Operation Type is set to a value that indicates to stop user plane DL data transmissions towards the UE and enable data buffering. The SMF starts data buffering for MT data if the data buffering is handled in SMF. 4. If data buffering is handled in the UPF, the SMF updates the UPF with proper rules for MT data handling. 5. The SMF sends the Nsmf_PDUSession_UpdateSMContext response. 6. The AMF sends N2 MT Communication Handling response message to NG-RAN acknowledging the NG-RAN request and indicating the AMF has taken the NG-RAN request into account. The AMF considers the UE is in CM-CONNECTED with RRC_INACTIVE state. 7. If the UE connection is not released as specified in step 1a, the NG-RAN initiates state transition from RRC_CONNECTED to RRC_INACTIVE with RRC configuring the eDRX values as specified in TS 38.300[ NR; NR and NG-RAN Overall description; Stage-2 ]  [9].