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

Step | Description |
---|---|
1 |
A 5G session is established among UE, E-UTRAN, NG-RAN, MME, AMF, S-GW, and SMF+PGW-C. E-UTRAN initiates handover towards MME. |
2 | MME sends the Forward Relocation Request to AMF. |
3 |
AMF sends the Nsmf PDU Session CreateSMContext request to SMF+PGW-C. This request includes details on the UE PDN connection and handover state. |
4 |
SMF+PGW-C checks for the following procedures:
SMF+PGW-C sends the Nsmf PDUSession CreateSMContext Response to AMF. This response includes the N2 Setup Request with the UPF UL tunnel information. |
5 |
AMF sends the handover request to NG-RAN. |
6 |
NG-RAN sends the acknowledgment of the handover request to AMF. |
7 |
AMF sends the Nsmf PDU Session Update SMF Context Request to SMF+PGW-C. This request includes the handover request with the gNB DL tunnel information. |
8 |
SMF+PGW-C sends the Nsmf PDU Session Update SMF Context Response to AMF. |
9 |
AMF sends the Forward Relocation Response to MME. |
10 |
MME sends the Handover Command to E-UTRAN. |
11 |
E-UTRAN sends the Handover Command to UE. |
12 |
UE sends the message on handover completion to NG-RAN. |
13 |
NG-RAN sends the Handover Notify message to AMF. |
14 |
AMF sends the Nsmf PDU Session Update SMF Context Request to SMF+PGW-C after the completion of the handover. |
15 |
SMF+PGW-C sends the N4 Session Modification Request to UPF. This request is for updating the DL FAR with the gNB tunnel information. |
16 |
The 5G Tunnel is updated with gNB tunnel information for the DL data. UPF sends the N4 Modification Response to SMF+PGW-C. |
17 |
SMF+PGW-C sends the Nsmf PDU Session Update SMContext Response to AMF. |