3GPP 23.501 v20.2.0 — the document's own text

5.8.2.6.3 Reporting of Usage Information towards SMF

Taught in 13. Where the packets actually go (The 5G system architecture, in depth), 5. The connection, and what is promised on it (The 5G system architecture, overview).

The UPF shall support reporting of usage information to the SMF. The UPF shall be capable to support reporting based on different triggers, including:

Periodic reporting with period defined by the SMF.
Usage thresholds provided by the SMF.
Report on demand received from the SMF.

The SMF shall make sure that the multiple granularity levels required by the reporting keys in the Usage Reporting rules satisfy the following aggregation levels without requiring a knowledge of the granularity levels by the UPF:

PDU Session level reporting;
Traffic flow (for both charging and usage monitoring) level reporting as defined by the reporting keys in the Usage Reporting Rule (see the description above).

Based on the mapping between Monitoring key and PCC rule stored at the SMF, the SMF shall combine the reported information with session and subscriber related information which is available at the SMF, for Usage Monitoring reporting over the corresponding Npcf interface (N7 reference point).

Based on the mapping between Charging key and Sponsor Identity (if applicable) and PCC rule stored at the SMF, the SMF shall combine the reported information with session and subscriber related information which is available at the SMF, for offline and online charging reporting over the corresponding charging interfaces.

This functionality is specified in TS 32.255 [68].

The usage information shall be collected in the UPF and reported to the SMF as defined in 5.8.2.6, based on Monitoring Keys and triggers which are specified in TS 23.503 [45].