How it Works
The SMF provides an option to configure back-off timer value with failure condition and Cause value. For configuration details, see the Configuring Back-off Timer section in this guide.
The SMF detects if the UPF is down due to N4 path failure. If the UPF is down, SMF includes the configured back-off timer value and cause value in the N1 PDU Session Release Command while clearing PDU session.
In home-routed roaming scenario, vSMF includes the back-off timer and cause value in PDU Session Release Command message sent over N1 when any of the following conditions are met:
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hSMF detects that the hUPF is inactive due to path failure.
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vSMF detects that the vUPF is inactive due to path failure.
If the SMF or PGW-C detects that the IP addresses are exhausted, SMF includes the back-off timer and cause value in the N1 PDU Session Establishment Reject message or Create Session Response depending on the RAT type.
In the roaming scenario, if the hSMF detects that the IP addresses are exhausted, it sends PDU Session Create Error to vSMF with the back-off timer and cause values. Based on this value, vSMF includes the back-off timer and Cause value in N1 PDU Session Establishment Reject message.
Note | Encoding of back-off timer in PDU Release Command and PDU Establishment Reject is as defined in 3GPP TS 24.008—Mobile radio interface Layer 3 specification; Core network protocols; Stage 3. Encoding of back-off timer in Create Session Response is as defined in 3GPP TS 29.274—3GPP Evolved Packet System (EPS); Evolved General Packet Radio Service (GPRS) Tunnelling Protocol for Control plane (GTPv2-C); Stage 3. |