How it Works
The SMF utilizes the NF Failover to achieve the UDM failover support functionality. This section provides information on how the SMF handles message-level failures and the corresponding HTTP status code-based failures.
The UDM failover supports the following messages that are initiated from the SMF.
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UE-Connection-Management (UE-CM)
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Nudm_UECM_Registration
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Nudm_UECM_DeRegistration
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UE-Subscription-Management (UE-SDM)
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Nudm_SDM_Get
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Nudm_SDM_Subscribe
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Nudm_SDM_Unsubscribe
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During the PDU session lifecycle, the SMF exchanges the preceding messages at various stages with the UDM. Depending on the HTTP status code configured in the NRF failure profile, the SMF performs one of the following actions:
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Ignore
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Continue
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Terminate
The SMF provides the following actions to attempt the same request to other available UDM servers.
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retry-and-terminate
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retry-and-ignore
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retry-and-continue
When all the retry attempts fail, the SMF takes the appropriate failure handling action. For example, if the FH action is retry-and-terminate, the SMF terminates the call after all the attempts fail.
Note | The SMF allows dynamic changes to the failure handling template configuration. Any changes to the configuration apply only to the new calls. |
Scenario |
Service |
Message |
Condition |
Action |
Success Response |
Handling of Failure Response |
||
---|---|---|---|---|---|---|---|---|
Terminate |
Continue |
Ignore |
||||||
PDU Session Creation procedures in 5G, 4G, WiFi Inter-RAT Handover procedures |
UECM |
Nudm_ UECM _Registration |
If the Nudm UECM Registration is not done and the access type is not 4G |
Send the message |
Mark the Registration is successful |
Terminate call |
Continue call |
Continue call |
Nudm_UECM _DeRegistration |
If the Nudm UECM Registration is done |
Send the message |
No action |
Terminate call |
Terminate call |
Terminate call |
||
PDU Session Creation procedures in 5G, 4G, WiFi |
SDM |
Nudm_SDM_Get |
If skipping the subscription fetch config is not enabled |
Send the message |
Mark the subscription fetch is successful |
Terminate call |
Continue call |
Continue call |
Nudm_ SDM _Subscribe |
If the subscription fetch is successful |
Send the message |
No action |
Terminate call |
Continue call if the subscription is not done |
Continue call if the subscription is not done |
||
PDU Session Release procedures in 5G, 4G, WiFi |
SDM |
Nudm_SDM _Unsubscribe |
If the subscription fetch is successful and the registration isns |
Send the message |
No action |
Terminate call |
Continue call |
Continue call |
Note |
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