Network-Initiated Modification Call Flow for Active User Plane and UE in CM-Connected State
This section describes the network-initiated modification call flow when the UE is in CM-Connected State and the User Plane is activated. The network can be PCF, UDM, or SMF.

Step | Description |
---|---|
1 | The PCF sends the notification towards SMF with policy decision to apply. |
2 | The SMF sends an acknowledgement for the policy notification to the PCF. |
3 | The SMF identifies the changes in QoS model that occur due to policy decision and triggers the NAMF Communication N1 and N2 message transfer toward AMF. This message transfer includes details, such as PDU Session ID, N2 SM information, N1 SM information, and N1 and N2 transfer failure notification target address. N2 includes the PDU session resource modify request transfer IE and N1 includes the PDU session modification request. |
4 | As UE is in CM-Connected state, the AMF initiates N1 and N2 transfer response. This response includes the “200 OK” status code and “N1_N2_TRANSFER_INITIATED” cause. |
5 | The user plane modification procedures begin both towards RAN and UE. |
6 | After receiving a response from RAN, the AMF sends the NSMF PDU Session Update SM Context Request towards the SMF. This request contains the SM information of the N2 interface. |
7 | The SMF responds back to the AMF with “200 OK” status code for the NSMF PDU Session Update SM Context Request. |
8 | After receiving a response from the UE, the AMF sends the NSMF PDU Session Update SM Context Request toward SMF. This request contains the SM information of the N1 interface. |
9 | The SMF responds back to the AMF with “200 OK” status code for NSMF PDU Session Update SM Context Request. |
10 | Based on the new QoS information, the SMF initiates the N4 Modification procedure towards the UPF to modify the session. |
11 | The UPF modifies the session and sends the acknowledgement of modification to the SMF. |