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

5.12.3 Secondary RAT Periodic Usage Data Reporting Procedure

Taught in 15. Rules, and paying for them (The 5G system architecture, in depth), 6. One network behaving like several (The 5G system architecture, overview).

Periodic reporting of the Secondary RAT usage data is an optional function. When NG-RAN, as defined in bullet e) of clause 5.12.12, is configured with a "time interval for Secondary RAT usage data reporting", the NG-RAN shall send a RAN Usage Data Report message for periodic reporting purposes to the SMF only when the timer expires for a UE for which Secondary RAT usage data reporting is ongoing. The timer runs from the last usage reporting for the UE.