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

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