Non-roaming 5GS to EPS Handover with Alternate RAT Tunnel Creation Call Flow
This section describes the call flow of the non-roaming 5GS to EPS handover with alternate RAT tunnel creation.

Step | Description |
---|---|
1 |
A 5G session is established among UE, E-UTRAN, NGRAN, MME, AMF, S-GW, and SMF+PGW-C. NG-RAN initiates handover towards AMF. |
2 | AMF sends the Nsmf PDU Session Context Request to SMF+PGW-C. |
3 | SMF+PGW-C sends the Nsmf PDU Session CreateSMContext Response to AMF. This response includes details on the CP and UP tunnels for both the default and dedicated bearers. |
4 |
AMF sends the Relocation Request to MME. |
5 |
MME sends the Create Session Request to S-GW. |
6 |
S-GW sends the Create Session Response to MME. |
7 |
MME sends the Handover Request to E-UTRAN. |
8 |
E-UTRAN sends the acknowledgment of the Handover Request to MME. |
9 |
MME sends the Relocation Response to AMF. |
10 |
AMF sends the handover command to NG-RAN. |
11 |
NG-RAN sends the handover command to UE. |
12 |
UE sends the handover completion message to NG-RAN. |
13 |
The UL data path is set up among UE, E-UTRAN, NG-RAN, MME, AMF, S-GW, SMF+PGW-C, and UPF. E-UTRAN sends the Handover Notify message to MME. |
14 |
MME sends the notification on the relocation completion to AMF. |
15 |
AMF sends the acknowledgment message of relocation completion to MME. |
16 |
MME sends the Modify Bearer Request to S-GW. |
17 |
S-GW sends the Modify Bearer Request to SMF+PGW-C. |
18 |
SMF+PGW-C sends the N4 Session Modification Request to UPF. This request includes details for updating DL FAR with S-GW tunnel for both the default and dedicated bearers. |
19 |
The 4G Tunnels are updated with DL FAR information (S-GW tunnel information). SMF+PGW-C sends the Modify Bearer Response to S-GW. |
20 |
The DL data path is set up among UE, E-UTRAN, NG-RAN, MME, AMF, S-GW, SMF+PGW-C, and UPF. S-GW sends the Modify Bearer Response to MME. |