Call Flows
This section includes the following call flow.
| Step | Description |
|---|---|
| 1 | gNB sends the dedicated bearer creation failure information with the fallback cause through AMF. |
| 2 | EPS fallback timer starts. |
| With the successful EPS fallback following the 5G to 4G handover, steps 3 to12 occur. | |
| 3 | EPS triggers pending dedicated bearer creation. |
| 4 | Delay timer starts. |
| 5 | SMF (+S5-C) sends the PFCP session modification request to UPF (+S5-U). |
| 6 | PDR and FAR are created. |
| 7 | UPF (+S5-U) sends the PFCP session modification response to SMF (+S5-C). |
| 8 | The information on the created PDR with the GTP-U TEID is available. |
| 9 | SMF (+S5-C) sends the Create Bearer Request to S-GW. |
| 10 | S-GW sends the Create Bearer Response to SMF (+S5-C). |
| 11 | SMF (+S5-C) sends the PFCP Session Modification Request to UPF (+S5-U). |
| 12 | UPF (+S5-U) sends the notification of the successful dedicated bearer creation to PCF. |
| 13 | EPS Fallback Guard Timer stops. |
| 14 | PCF sends the “200 OK” acknowledgment to SMF (+S5-C). |
| In the EPS fallback timer expiry before handover completion scenario, steps 13 to15 occur. | |
| 15 | SMF (+S5-C) sends the failure notification of the dedicated bearer creation to PCF. |
| 16 | PCF sends the “200 OK” acknowledgment to SMF (+S5-C). |
| 17 | The 5G to 4G handover procedure continues. |