3GPP 24.501 v20.0.0 — the document's own text

5.5.1.3.3 5GMM common procedure initiation

Taught in 4. Inside TS 24.501, the document at the centre (CT1 — the group that writes what your phone says, overview).

The AMF may initiate 5GMM common procedures, e.g. the identification, authentication and security procedures during the registration procedure, depending on the information received in the REGISTRATION REQUEST message.

The AMF may be configured to skip the authentication procedure even if no 5GS security context is available and proceed directly to the execution of the security mode control procedure as specified in clause 5.4.2, during the registration procedure for mobility and periodic registration update for a UE that has only an emergency PDU session.

The AMF shall not initiate a 5GMM authentication procedure before completion of the registration procedure for mobility and periodic registration update, if the following conditions apply:

the UE initiated the registration procedure for mobility and periodic registration update after handover or inter-system change to N1 mode in 5GMM-CONNECTED mode;
the target cell is a shared network cell; and

c.1) the UE has provided its 5G-GUTI in the 5GS mobile identity IE or the Additional GUTI IE in the REGISTRATION REQUEST message, and the PLMN identity included in the 5G-GUTI is different from the selected PLMN identity of the target cell; or

c.2) the UE has included the 5G-GUTI mapped from the 4G-GUTI in the 5GS mobile identity IE and not included an Additional GUTI IE in the REGISTRATION REQUEST message, and the PLMN identity included in the 5G-GUTI is different from the selected PLMN identity of the target cell.