N4 Path Failure Handling Call Flow

This section describes how the SMF handles the N4 path failures observed in non-roaming and roaming scenarios.

Handling of N4 Path Failures in Non-roaming Session

The following figure illustrates the N4 path failure handling call flow for a non-roaming session.

N4 Path Failure Handling Call Flow for Non-roaming Session
N4 Path Failure Handling Call Flow Description for Non-roaming Session

Step

Description

1

The SMF checks if the UPF is inactive due to N4 path failure.

2

If the SMF detects that the UPF is inactive, it fetches the back-off timer and cause value from the DNN profile configuration. The SMF sends the timer and cause value in the N1 PDU Session Release Command to AMF. Then, the SMF performs the PDU clean up.

Handling of N4 Path Failures in vUPF During Roaming Session

The following figure illustrates the call flow of handling N4 path failures in vUPF during the roaming session.

vUPF Path Failure Handling Call Flow for Roaming Session
vUPF Path Failure Handling Call Flow Description for Roaming Session

Step

Description

1

The vSMF checks if the vUPF is inactive due to N4 path failure.

2

If the vSMF detects that the vUPF is inactive, it fetches the back-off timer value and cause from the DNN profile configuration. The vSMF sends the timer and cause value in the N1 PDU Session Release Command to AMF. Then, the vSMF performs the PDU clean up.

Handling of N4 Path Failures in hUPF During Roaming Session

The following figure illustrates the call flow of handling N4 path failures in hUPF during the roaming session.

hUPF Path Failure Handling Call Flow for Roaming Session
hUPF Path Failure Handling Call Flow Description for Roaming Session

Step

Description

1

The hSMF checks if the hUPF is inactive due to N4 path failure.

2

If the hUPF is inactive, hSMF sends the back-off timer and cause to vSMF through the N16 update request.

3

The vSMF includes the back-off timer and cause value in N1 PDU Session Release Command message.