WiFi to LTE Handover

The following illustration describes the WiFi to LTE handover call flow.

WiFi to LTE Handover Call Flow Description
Step Description
1

N4 Session is established for WiFi between SMF/IWF and UPF.

The MME sends Create Session Request (relocating to 4G) to the SGW-C/cnSGW.

2 The SGW-C/cnSGW sends Sx Session Establishment Request (No F-TEID) to the UPF.
3

IMSI-based lookup is done at SxDemux for SessMgr ID.

The UPF sends Sx Establishment Response to the SGW-C/cnSGW.

4 The SGW-C/cnSGW sends Create Session Request to the SMF/IWF.
5 The SMF/IWF sends Sx Modify Request with new Uplink RB PDR to the UPF.
6 The UPF sends Sx Modify Response to the SMF/IWF with new TEID for Uplink data.
7 The SMF/IWF sends Create Session Response to the SGW-C/cnSGW.
8 The SGW-C/cnSGW sends Sx Modify Request to the UPF with updated Uplink FAR.
9

Uplink path is established.

The UPF sends Sx Modify Response to the SGW-C/cnSGW.

10 The SGW-C/cnSGW sends Create Session Response to the MME.
11 The MME sends Modify Bearer Request to the SGW-C/cnSGW.
12 The SGW-C/cnSGW sends Sx Modify Request to the UPF with eNodeB TEIDs.
13 The UPF sends Sx Modify Response back to the SGW-C/cnSGW.
14 The SGW-C/cnSGW sends Modify Bearer Request to the SMF/IWF.
15 The SMF/IWF sends tunnel switch Sx Modify Request to the UPF.
16

Collapsed datapath with Sxa session is established at UPF.

The UPF sends Sx Modify Response to the SMF/IWF.

17 The SMF/IWF sends Modify Bearer Response to the SGW-C/cnSGW.
18 The SGW-C/cnSGW sends Modify Bearer Response to the MME.