4G to 5G Handover Flow for Pure-S Call Flow

This section describes the 4G to 5G Handover flow for Pure-S call flow.

4G to 5G Handover Flow for Pure-S Call Flow
4G to 5G Handover Flow for Pure-S Call Flow Description

Step

Description

1

4G call is established.

The E-UTRAN sends the Handover Required message to the MME.

2

The MME sends the Forward Relocation Request to the AMF.

3

The AMF sends the Handover Request message to the NG-RAN.

4

The AMF receives Handover Request ACK message.

5

The MME receives the Forward Relocation Response from the AMF.

6

The MME sends the Create IDFT Request with the Bearer Context with the eNodeB DL and UL FWD FTEID, to the Target SGW-C.

7

The Target SGW-C sends the Sx Modification Request with Create PDRs and FARs to the Target SGW-U.

8

The Target SGW-U sends the Sx Modification Response with Create PDRs and FARs to the Target SGW-C.

9

The Target SGW-C sends the Create IDFT Request with the Bearer Context along with eNodeB DL and UL FWD FTEID to the MME.

10

The MME sends the Create IDFT Request with the Bearer Context along with target SGW DL and UL FWD FTEID to the Source SGW-C.

11

The Source SGW-C sends the Sx Modification Request with Create PDRs and FARs to the Source SGW-U.

12

The Source SGW-C receives the Sx Modification Response with Create PDRs and FARs from the Source SGW-U.

13

The MME receives the Create IDFT Response with the Bearer Context along with SGW DL and UL FWD FTEID, from the Source SGW-C.

The PDN sends the Downlink Data to the Source SGW-U, and the Source SGW-U sends the Downlink Data to the Source eNodeB.

The indirect forwarding data (IDFT Tunnel) starts from the Source eNodeB to the Target SGW-U, and from the Target SGW-U to the Target eNodeB.

The Target eNodeB sends the Downlink Data to the UE.

The UE sends Uplink Data to the Source eNodeB, and the Source eNodeB sends the Uplink Data to the Source SGW-U.

The Source SGW-U sends the indirect forwarding data to the Target SGW-U, and the Target SGW-U sends the indirect forwarding data to the Target eNodeB.

14

The MME sends the Modify Bearer Request to the Target SGW-C.

15

The MME receives the Modify Bearer Response from the Target SGW-C.

16

The MME sends the Delete IDFT Request to the Target SGW-C.

17

The Target SGW-C sends the Sx Modification Request to the Target SGW-U, to remove the PDRs and FARs.

18

The Target SGW-C receives the Sx Modification Response from the Target SGW-U.

19

The MME receives the Delete IDFT Response from the Target SGW-C.