Section: I.9.2.3 Primary authentication using DCS
Content: When the primary authentication is performed between the UE and the DCS, the authentication requirements and procedures defined in clause I.2 for Credential Holder shall apply with the DCS taking the role of the Credentials Holder. When the DCS uses AAA Server for primary authentication, AUSF directly selects the NSSAAF as specified in 23.501 [2]. In this case, the UDM is not involved in the procedure defined in clause I.2.2.2.2, and the step 3 to step 5 shall be skipped. When 5G AKA or EAP-AKA’ is used, the DCS shall act as a AUSF/UDM. The choice of primary authentication method used between the UE and the DCS is left to the decision of the DCS. When the primary authentication is performed between the UE and the DCS via the AUSF using EAP-TTLS, Annex U can be used.