How It Works
The EPS fallback timer starts after receiving the notification for dedicated bearer creation failure with the EPS fallback cause from gNB through AMF. In this case, SMF does not send the failure notification to PCF and waits for 5G to 4G handover to complete. Then, SMF triggers the bearer creation in 4G. The EPS fallback timer stops on the completion of the 5G to 4G handover.
In case the timer expires before the completion of the 5G to 4G handover, SMF sends a notification for dedicated bearer creation failure to PCF. Then, the new statistics counter, with the “smf_eps_fb” and “timeout” labels, is incremented. However, the 5G to 4G handover procedure continues.