3GPP 24.501 v20.0.0 — the document's own text
8.2.7.38 Negotiated NB-N1 mode DRX parameters
Taught in 4. Inside TS 24.501, the document at the centre (CT1 — the group that writes what your phone says, overview).
The network shall include the Negotiated NB-N1 mode DRX parameters IE if the requested NB-N1 mode DRX parameters IE was included in the REGISTRATION REQUEST message.