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

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

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

Step

Description

1

5G call is established.

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

2

The AMF sends the Relocation Request to the MME.

3

The MME sends the Create Session Request to the Target SGW-C.

4

The MME receives the Create Session Response from the Target SGW-C.

5

The MME sends the Handover Request to the E-UTRAN.

6

The MME receives the Handover Request ACK from the E-UTRAN.

7

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

8

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

9

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

10

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

11

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

12

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

13

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

14

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

15

The MME sends the Relocation Response to the AMF.

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

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

16

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

17

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

18

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

19

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

20

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

21

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