5G to Wi-Fi Handover with Alternate RAT Tunnel Creation Call Flow

This section describes the call flow of the 5G to Wi-Fi handover with an alternate RAT tunnel creation.

5G to Wi-Fi Handover with Alternate RAT Tunnel Creation Call Flow Description
Step	Description
1	ePDG sends the Create Session Request to SMF+PGW-C. This request includes details on S2bC F-TEID and S2bU F-TEID.
2	SMF+PGW-C sends the Policy Update Request to PCF.
3	PCF sends the Policy Update Response to SMF+PGW-C.
4	SMF+PGW-C sends the Charging Update Request to CHF.
5	CHF sends the Charging Update Response to SMF+PGW-C.
6	SMF+PGW-C sends the Create Session Response to ePDG. This response includes details on the stored Wi-Fi UL tunnel.
7	SMF+PGW-C sends the Create Bearer Request to ePDG. This request includes details on the dedicated bearers with UL tunnel.
8	ePDG sends the Create Bearer Response (DL tunnel information) to SMF+PGW-C.
9	SMF+PGW-C sends the N4 Modification Request to UPF. This request includes information on the DL FAR update and Query URR of gNB tunnel.
10	UPF sends the N4 Modification Response to SMF+PGW-C.
11	SMF+PGW-C sends the N1N2Message Transfer, which is the PDU Session Release Command to AMF.
12	AMF sends the 200 OK response to SMF+PGW-C.
13	AMF sends the SMContext Update Request (N2Message) to SMF+PGW-C.
14	SMF+PGW-C sends the SMContext Update Response (204 OK) to AMF.
15	AMF sends the SMContext Update Request (N1Message) to SMF+PGW-C.
16	SMF+PGW-C sends the SMContext Update Response (204 OK) to AMF.
17	SMF+PGW-C sends the SMContext Status Notification to AMF. This notification indicates the resource status as RELEASED.
18	AMF sends the 204 OK response to SMF+PGW-C. Then, on SMF+PGW-C, the policy and charging updates happen.