CHF Server Reconciliation
The SMF falls back to the first available offline CHF server when the NF selected by NRF discovery is unreachable. The CHF Reconciliation feature involves deleting the existing subscribers that are associated to a set of offline NFs, and the subscribers that are in offline fallback mode.
The CHF server reconciliation works when any of the following two conditions are met:
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if the NRF detects that an offline CHF server is now active
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if the RAR is recieved from the CHF server on an offline converted session
For the condition #2, the session gets deleted directly. With the NRF discovery, this feature involves the following steps:
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SMF subscribes for the notification of NF instance IDs from NRF through NF_LIB component of Rest-ep.
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If the NF discovery query determines that all the NFs are down, the NF_LIB component treats these set of NFs as offline. If any one of the NFs is available again, the NRF triggers notification for the same to the SMF.
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The SMF performs NRF discovery after re-validation timer. If the NRF detects any new NF, the SMF receives the corresponding notification from the NRF.
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When the SMF learns that an NF is online and it satisfies the NF discovery query parameters, then the SMF initiates the CHF server reconciliation.
The following labels are introduced as part of this feature:
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disc_pdurel_chf_reconciliation: This label is defined under SMF_DISCONNECT_STATS to indicate the disconnect reason.
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chf_reconl_pdu_sess_rel: This label is defined under smf_service_stats metric to display the number of times the PDU session release procedure is initiated.