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.

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.

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.

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. |