Non 3GPP Untrusted LTE to WiFi Handover
This section describes the non-3GPP untrusted LTE to WiFi handover call flow.

Step |
Description |
---|---|
1 |
Session is established in LTE with a default bearer and dedicate bearer with 8 TFTs. |
2 |
LTE to Wi-Fi Handover is triggered, when CSReq is received with hi flag configured from ePDG. |
3 |
After successfully handling CSReq, CSResp is sent back to ePDG, indicating that the default bearer is successfully handed over. |
4 |
For the dedicated bearer which has 8 TFT, since all TFTs cannot be sent in CBReq, the CBReq message is triggered with only 4 TFTs toward ePDG. |
5 |
After successful CBResponse from ePDG, SMF sends the remaining TFTs in the UBReq message. |
6 |
After successful UBResponse from ePDG, SMF continues with completion of establishing the bearer towards UPF. |
7 |
In case of failure in CBResponse or failure in UBResponse at Step 5 or Step 6, the SMF deletes that bearer, and if armed, sends rule report to PCF with corresponding rules information as Inactive. |
Important | Steps 4-7 are applicable for LTE to Wi-Fi and NR to Wi-Fi if a dedicate bearer has more than 4 TFTs. |