Initial Attach with SGW-C/cnSGW and SMF/IWF
The following illustration describes the initial attach call flow with collapsed UPF.

| Step | Description |
|---|---|
| 1 | Create Session Request (CSReq) is received by SGW-C/cnSGW and it selects the UPF. |
| 2 |
The SGW-C/cnSGW sends Sx Establishment Request (Sxa) to the UPF. The UPF:
|
| 3 | The UPF sends Sx Establishment Response (Sxa) back to SGW-C/cnSGW. |
| 4 |
The SGW-C/cnSGW sends CSReq to SMF/IWF. The SMF/IWF selects the same UPF that is selected by SGW-C/cnSGW. |
| 5 | The SMF/IWF sends Sx Establishment Request (N4) to the UPF. |
| 6 | The UPF sends Sx Establishment Response (N4) to the SMF/IWF. |
| 7 | The SMF/IWF sends Create Session Response to the SGW-C/cnSGW. |
| 8 |
The SGW-C/cnSGW sends Sx Modify Request (Sxa) to the UPF. The UPF updates P-GW data F-TEID as part of Egress FAR. The UPF also interconnects Sxa and N4 session using internal logic and removes already-created Bearer Stream (3 tuple). |
| 9 | The UPF sends Sx Modify Response (Sxa) 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 (Sxa) to the UPF. The UPF updates eNodeB F-TEID as part of Ingress FAR. |
| 13 | The UPF sends Sx Modify Response to the SGW-C/cnSGW. |
| 14 | The SGW-C/cnSGW sends Modify Bearer Response to the MME. |