CHF and PCF Integration for N26 4G to 5G Handover Call Flow

This section describes the call flow for the CHF and PCF Integration for N26 4G to 5G handovers.

CHF and PCF Integration for N26 4G to 5G Handover Call Flow
CHF and PCF Integration for N26 4G to 5G Handover Call Flow Description
StepDescription
1

The PDU session is established over MME, SGW, 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.

2

The T-AMF sends SM Context Create Request to the SMF. This request includes information on handover state as preparing, UE location, UE time zone, serving NFID, serving network, and RAT type.

2aThe SMF detects access-side changes that are received in the SM Context Create 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 N26-based Handover Preparation procedure starts from T-AMF toward the SMF or PGW-C and UHF and vice versa, as defined in 3GPP TS 23.502, section 4.1.9.3.
4In the N26 Handover Execution procedure, the UPF sends the usage report as part of N4 modification response to SMF. The SMF holds the final SM Context Update Response when the SMF detects the CHF or PCF triggers.
5The 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 and usage report), customer identification, and PDU session charging information.
6The 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.
6aThe 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.
7The SMF posts the internal transaction to send the SM policy update information for PCF triggers.
8The SMF sends the SM Context Update Response, for which the handover state is complete, to the AMF.
9The SMF sends the SM Policy Control Update information to the PCF. The SM Policy Control Update includes details, such as the user location information, UE time zone, and serving network.
10The PCF sends the SM Policy Control Update Response, which is the SM policy decision, to the SMF.
11The SMF processes the SM policy decision that is received as response and handles the response as PCF Initiation Modify procedure, as defined in 3GPP TS 23.502, section 4.3.3.2.