Section: 4.8.1.2 Connection Suspend procedure
Content: This procedure may be initiated by the serving NG-RAN node when the UE is in CM-CONNECTED and has at least one PDU session with active user plane connection and NG-eNB has received indication from the AMF that User Plane CIoT 5GS Optimisation, as defined in clause 5.31.18 of TS 23.501[ System architecture for the 5G System (5GS) ]  [2], is supported for the UE. Figure 4.8.1.2-1: NG-RAN initiated Connection Suspend procedure 1. NG-RAN to AMF: The NG-RAN sends the N2 Suspend Request message to the AMF, see TS 38.413[ NG-RAN; NG Application Protocol (NGAP) ]  [10]. The AMF enters CM-IDLE with Suspend indicator. Context information related to the NGAP UE association, UE Context and PDU session context, necessary to resume the connection is stored in the UE, NG-RAN node and in the AMF. The NG-RAN may include the Suspend cause and the N2 SM information. If the UE is served by an NG-eNB that supports WUS, then the NG-eNB should include the Information On Recommended Cells And RAN nodes For Paging in the N2 Suspend Request message; otherwise NG-RAN may include the Information On Recommended Cells And NG-RAN For Paging in the N2 Suspend Request message. If available, the AMF shall store this information to be used when paging the UE. The NG-RAN includes Information for Enhanced Coverage, if available, in the N2 Suspend Request message. If Service Gap Control is being applied to the UE (see clause 4.3.17.9) and the Service Gap timer is not already running, the Service Gap timer shall be started in the AMF when entering CM-IDLE, unless the connection was initiated after a paging of an MT event, or after a mobility registration procedure without Follow-on Request indication or after a mobility registration procedure for regulatory prioritized services like Emergency services or exception reporting. 2. AMF to SMF: For each of the PDU Sessions in the N2 Suspend Request, 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)). The Operation Type is set to "UP Suspend" to indicate suspend of user plane resources for the PDU Session. 3. SMF to UPF: N4 Session Modification Request (AN Tunnel Info to be suspended, Buffering on/off). The SMF initiates an N4 Session Modification procedure indicating the need to release the tunnel info of AN terminating N3 between AN and UPF. Buffering on/off indicates whether the UPF shall buffer incoming DL PDU or not. The UPF sends N4 Session Modification Response to acknowledge the SMF request. The SMF shall maintain the N3 tunnel info (including both AN Tunnel Info and the CN Tunnel Info). NOTE: The UPF maintains the CN tunnel info as it may receive uplink packets from the AN. 4. SMF to AMF: The SMF sends Nsmf_PDUSession_UpdateSMContext response to the AMF. 5. AMF to NG-RAN: After response for each PDU session in step 4, the AMF sends N2 Suspend Response to NG-RAN to successfully terminate the Connection Suspend procedure initiated by the NG-RAN, see TS 38.413[ NG-RAN; NG Application Protocol (NGAP) ]  [10]. 6. The NG-RAN sends RRC message to suspend the RRC Connection towards the UE including UE Resume ID, see TS 36.300[ Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Radio Access Network (E-UTRAN); Overall description; Stage 2 ]  [46]). If Service Gap Control is applied for the UE (see clause 5.31.16 of TS 23.501[ System architecture for the 5G System (5GS) ]  [2]) and the Service Gap timer is not already running, the Service Gap timer shall be started in the UE when entering CM-IDLE, unless the connection was initiated as a response to paging of an MT event, or after a mobility registration procedure without Follow-on Request Indication set or after a mobility registration procedure for regulatory prioritized services like Emergency services or exception reporting.