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

4.4.2.0 General

Taught in 21. Emergency calls, messages, voice and location (The 5G system architecture, in depth).

This clause introduces legacy SMS over NAS architecture, in which the interfaces between SMSF/UDM and SMS-GMSC/SMS-IWMSC/IP-SM-GW/SMS Router are still based on legacy protocol (i.e. MAP or Diameter).

The SBI-based SMS architecture and interfaces are specified in TS 23.540 [142].