IDFT Handling during S1 Handover
The following illustration describes the IDFT handling during S1 handover with collapsed UPF.

| Step | Description |
|---|---|
| 1 |
As part of initial attach, N4 and Sxa session is already established with SMF and UPF. S1 handoff is triggered. The MME sends Indirect Tunnel Request Message to the SGW-C/cnSGW. |
| 2 |
The SGW-C/cnSGW sends Sx Modify Request (Sxa) to the UPF. At UPF:
|
| 3 | The UPF sends Sx Modify Response (Sxa) to the SGW-C/cnSGW. |
| 4 | The SGW-C/cnSGW sends Create Indirect Tunnel Response Message to the MME. |
| 5 | The Source eNodeB sends IDFT data packet to the UPF. If there’s no matching 3 tuple stream at UPF, the packet is forwarded to SessMgr. |
| 6 | The UPF sends IDFT data packet to the destination eNodeB. |