Handling Failed QoS Flow Identifier During PDU Session Modification
The SMF supports handling of the failed QoS flows over N2 interface during the PDU session modification.
If the modification of a PDU session or a QoS flow fails, the NG-RAN node falls back to the older configuration. That is, it falls back to the configuration of the session or the flow that was available before receiving the PDU SESSION RESOURCE MODIFY REQUEST message.
The SMF receives the QoS Flow Identifier for which the flow add/modify failed during the PDU SESSION RESOURCE MODIFY REQUEST.
If the new flow addition fails, the SMF performs the following:
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Removes the failed flow towards N1 (UE)
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Stops sending the failed flow-related information towards N4 (UPF)
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Stops sending the failed flow-related information towards N40 (CHF)
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Checks if the triggers are enabled and then sends the rule report for the failed flow towards N7 (PCF).
If the modification of flow fails, the SMF performs the following:
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Replaces the old information for the failed flow towards N1 (UE)
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Stops sending the modified flow-related information towards N4 (UPF)
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Stops sending the modified flow-related information towards N40 (CHF)
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Checks if the triggers are enabled and then sends the Rule Report for the failed flow towards N7 (PCF).
The following table captures the SMF behavior for the cause values included in the PDU Session Resource Modify Unsuccessful Transfer IE. These cause values are applicable for the PDU session modification procedure.
Cause Group |
Cause Value |
SMF Behavior |
Comment |
---|---|---|---|
Radio Network Layer Cause |
|||
Unspecified |
General |
||
Unknown PDU Session ID |
Delete the session |
N1 FiveGSM Cause reactivation requested |
|
Unknown QoS Flow ID |
Send delete details to N1 Send PCF report about rule(s) |
||
Multiple PDU Session ID Instances |
Delete the session |
||
Multiple QoS Flow ID Instances |
Delete the session |
N1 FiveGSM Cause reactivation requested |
|
Xn handover triggered |
Act based on collision handling |
||
Not supported 5QI value |
Send delete details to N1 Send PCF report about rule(s) |
||
IMS voice EPS fallback or RAT fallback triggered |
Already supported |
||
Transport Layer Cause |
|||
Transport resource unavailable |
Send delete details to N1 Send PCF report about rule(s) |
||
Unspecified |
|||
NAS Cause |
|||
Normal release |
Delete the session |
||
Authentication failure |
Delete the session |
||
Deregister |
Delete the session |
||
Unspecified |
Delete the session |
||
Protocol Cause |
|||
Transfer syntax error |
N1 rollback Error log fail procedure |
||
Abstract syntax error (reject) |
N1 rollback Error log fail procedure |
||
Abstract syntax error (ignore and notify) |
N1 rollback Error log fail procedure |
||
Message not compatible with receiver state |
N1 rollback Error log fail procedure |
||
Semantic error |
N1 rollback Error log fail procedure |
||
Abstract syntax error (falsely constructed message) |
N1 rollback Error log fail procedure |
||
Unspecified |
N1 rollback Error log fail procedure |
||
Miscellaneous Cause |
|||
Control processing overload |
N1 rollback Error log fail procedure |
||
Not enough user plane processing resources |
N1 rollback Error log fail procedure |
||
Hardware failure |
Delete the session |
||
O&M intervention |
N1 rollback Error log fail procedure |
||
Unknown PLMN |
Delete the session |
Bulk Statistics
The following statistics provide details about the failed QoS flows over the N2 interface.
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policy_pdu_flows_total
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total attempted
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total succeeded
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total failed
-
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policy_pdu_flows_current
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current attempted
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current succeeded
-
current failed
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