Call Flows

This section includes the following call flow.

EPS Fallback Guard Timer Call Flow


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