UE-Initiated PDU Session Modification Call Flow
This section describes the UE-Initiated PDU Session Modification call flow.
The PDU Session Modification is required when one or several of the QoS parameters exchanged between the UE and the network needs to be modified.

Step |
Description |
---|---|
1, 2, 3 |
The UE initiates the PDU Session Modification procedure by the transmission of an NAS message (N1 SM container (PDU Session Modification Request (PDU session ID, Packet Filters, Operation, Requested QoS, Segregation, 5GSM Core Network Capability)), and PDU Session ID) message. The AMF invokes the Nsmf_PDUSession_UpdateSMContext Request towards the SMF. |
4 |
The SMF responds to the AMF through Nsmf_PDUSession_UpdateSMContext (N2 SM information (PDU Session ID, QFI(s), QoS Profile(s), Session-AMBR), N1 SM container (PDU Session Modification Command (PDU Session ID, QoS parameters, Session-AMBR))). The N2 SM information carries information that the AMF provides to the RAN. It may include the QoS profiles and the corresponding QFIs to notify the RAN that one or more QoS flows were added, or modified. It may include only QFI(s) to notify the RAN that one or more QoS flows were removed. The N2 SM information provided to the RAN includes information for establishment of User Plane resources. The N1 SM container carries the PDU Session Modification Command that the AMF provide to the UE. |
5 |
The SMF invokes Namf_Communication_N1N2MessageTransfer (N2 SM information (PDU Session ID, QFI(s), QoS Profile(s), Session-AMBR), N1 SM container (PDU Session Modification Command (PDU Session ID, QoS rule(s), QoS parameters, and Session-AMBR). |
6 |
The AMF sends N2 PDU Session Request (N2 SM information received from SMF, NAS message (PDU Session ID, N1 SM container (PDU Session Modification Command)) Message to the RAN. |
7 |
The RAN issues AN-specific signaling exchange with the UE that is related with the information received from SMF. |
8 |
The RAN acknowledges N2 PDU Session Request by sending a N2 PDU Session Ack (N2 SM information (List of accepted/rejected QFI(s), AN Tunnel Info, PDU Session ID), User location Information) Message to the AMF. |
9, 10 |
The AMF forwards the N2 SM information and the User location Information received from the AN to the SMF through Nsmf_PDUSession_UpdateSMContext service operation. The SMF replies with a Nsmf_PDUSession_UpdateSMContext Response. |
11 |
The UE acknowledges the PDU Session Modification Command by sending a NAS message (PDU Session ID, N1 SM container (PDU Session Modification Command Ack)) message. |
12 |
The RAN forwards the NAS message to the AMF. |
13 |
The AMF forwards the N1 SM container (PDU Session Modification Command Ack) and User Location Information received from the AN to the SMF through Nsmf_PDUSession_UpdateSMContext service operation. The SMF replies with a Nsmf_PDUSession_UpdateSMContext Response. |