Connected Mode Call Flow
The following figure illustrates the flow for Service Request triggered by UE in Connected mode.

Step |
Description |
---|---|
1 |
UE initiates Service Request procedure by sending Service Request to (R)AN : AN message (AN parameters, Service Request (List Of PDU Sessions To Be Activated, List Of Allowed PDU Sessions, security parameters, PDU Session status)). The Service Request message is sent in UPLINK NAS TRANSPORT Message. |
2 |
AMF determines the PDU Session(s) to be activated and sends an Nsmf_PDUSession_UpdateSMContext Request to SMF(s) associated with the PDU Session(s) with upCnxState set to "ACTIVATING". AMF also initiates PDU Session Release procedure in the network for the PDU Sessions whose PDU Session ID(s) were indicated by the UE as not available in the PDU Session status. |
3 |
For a PDU Session that the SMF has determined to accept the activation of UP connection, the SMF sends Nsmf_PDUSession_UpdateSMContext Response with N2 SM information to the AMF. The N2 SM information contains information that the AMF provides to the NG-RAN. If SMF rejects the activation of UP of the PDU Session, it sends Nsmf_PDUSession_UpdateSMContext Response with cause. |
4 |
AMF to (R)AN: If the Service Request was triggered in CM-IDLE state, AMF sends Initial Context Setup Request with the N2 SM information received from SMF, MM NAS Service Accept and the other required parameters. If the Service Request was triggered in CM-CONNECTED state, AMF sends PDU Session Resource Setup Request with N2 SM information received from SMF and MM NAS Service Accept. MM NAS Service Accept includes PDU Session status in AMF. If the activation of UP of a PDU Session is rejected by an SMF, then the MM NAS Service Accept includes the PDU Session ID and the cause why the User Plane resources were not. Any local PDU Session Release during the Service Request procedure is indicated to the UE via the Session Status. If there are multiple PDU Sessions that involves SMF update, AMF waits for response from all SMFs before sending N2 SM information and MM NAS Service Accept to the RAN. |
5 |
AMF receives N2 Request Ack and if this contains N2 SM information, then it sends Nsmf_PDUSession_UpdateSMContext Request per PDU Session with this information to the SMF. |