CHF and PCF Integration for Intra-AMF and Inter-AMF N2-Based Handovers Call Flow

This section describes the call flow for the CHF and PCF Integration for Intra-AMF and Inter-AMF N2-based handovers.

CHF and PCF Integration for Intra-AMF and Inter-AMF N2-Based Handovers Call Flow
CHF and PCF Integration for Intra-AMF and Inter-AMF N2-Based Handovers Call Flow Description
StepDescription
1

The PDU session is established over S-AMF and SMF by communicating with UPF, PCF, or CHF for IPv4, IPv6, or dual-stack.

The PCF provides Policy Control Request trigger for SM policy decision as response to the request for creation of SM policy control.

The CHF provides session-level and rating-group-level triggers to SMF as the Charging Data Create Response.

2The T-AMF sends SM Context Update Request by including handover state to the SMF. The handover state includes the information on preparation, UE location, UE time zone, target serving NFID, and serving network. The AMF includes target serving NFID information for inter-AMF handoff.
2aThe SMF detects access-side changes that are received in the SM Context Update Request and the charging triggers with the information that is available in Step 2.
2bThe SMF detects the PCF triggers with the information that is available in Step 2.
3The N2-based Handover Preparation procedure starts from T-AMF towards the SMF and CHF and vice-versa.
4In the N2-based Handover Execution procedure, in case of inter-AMF handoff, the SMF receives SM Context Release Request from S-AMF and responds with the SM Context Release Response to the S-AMF.
5In N2-based Handover Execution procedure, the UPF provides the usage report as part of N4 modification response. The SMF holds the final SM Context Release Response when the SMF detects the CHF or PCF triggers.
6The SMF sends the Charging Data Update Request to the CHF. This request includes the information on session-level triggers, multi-unit-Information (with rating-group-level triggers with usage report), customer identification, and PDU session charging information.
7The CHF sends the Charging Data Update Response with optional multi-unit-information. The CHF also sends the new session or rating-group-level triggers to the SMF.
7aThe SMF processes the Charging Data Update Response and updates the PDU session. The SMF does not send the N4 modification request to the UPF for the newly received information from the CHF.
8The SMF posts the internal transaction to send the SM policy update information for PCF triggers.
9The SMF sends the SM Context Update Response, for which the handover state is complete, to the T-AMF.
10The SMF sends the SM Policy Control Update information to the PCF. The SM Policy Control Update information includes details, such as the user location information, UE time zone, and serving network.
11The PCF sends the SM Policy Control Update Response, which is the SM policy decision, to the SMF.
12The SMF processes the SM policy decision that is received as response and handles the response as PCF Initiation Modify procedure.