Initial Attach with SGW-C/cnSGW and SMF/IWF

The following illustration describes the initial attach call flow with collapsed UPF.

Initial Attach with SGW-C/cnSGW and SMF/IWF Call Flow Description
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:

  • Allocates Sxa session

  • Allocates S-GW Ingress and Egress local F-TEID

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.