3GPP 23.501 v20.2.0 — the document's own text
4.4.2.2 Reference point to support SMS over NAS
Taught in 21. Emergency calls, messages, voice and location (The 5G system architecture, in depth).
N1: Reference point for SMS transfer between UE and AMF via NAS.
Following reference points are realized by service based interfaces:
N8: Reference point for SMS Subscription data retrieval between AMF and UDM.
N20: Reference point for SMS transfer between AMF and SMS Function.
N21: Reference point for SMS Function address registration management and SMS Management Subscription data retrieval between SMS Function and UDM.