The Unified Data Management (UDM) is a fundamental Network Function (NF) within the 5G Core's Service-Based Architecture. Its primary role is to manage and provide access to a unified database containing user subscription information. This includes user identification (SUPI), authentication credentials, access authorization policies, and mobility/session subscription data. The UDM exposes these functionalities as services (e.g., NudmSubscriberDataManagement, NudmUEAuthentication) over the Service-Based Interface (SBI) to other authorized NFs, such as the Access and Mobility Management Function (AMF), Session Management Function (SMF), and Authentication Server Function (AUSF). It acts as a front-end to the Unified Data Repository (UDR).

B. This describes the Authentication Server Function (AUSF), which is responsible for executing the authentication procedures, using credentials it obtains from the UDM.

C. The UDM is a network function, not a data repository. It manages structured data stored in the Unified Data Repository (UDR), not unstructured data.

D. This describes the Network Repository Function (NRF), which maintains a registry of available NF instances and their profiles, enabling service discovery within the 5G Core.

1. 3GPP TS 23.501, "System architecture for the 5G System (5GS); Stage 2" (Release 17).

Section 6.2.3, Unified Data Management (UDM): This section explicitly defines the UDM's functionalities, including generation of authentication credentials, user identification handling, access authorization, and subscription management. It also details how the UDM provides services to the AMF, SMF, and AUSF.

2. Nokia, "Cloud native data and identity management for the 5G era" White Paper.

Page 4, "Nokia Unified Data Management": This document describes the Nokia UDM as a function that "manages subscription information for the 5G core" and "provides this information to the AMF, SMF and AUSF network functions." This directly supports the description in option A.

3. A. A. N. Abdalla, M. A. M. Ali and H. S. Ali, "A Comprehensive Survey on 5G Core (5GC) Network," 2021 International Conference on Computer, Control, Electrical, and Electronics Engineering (ICCCEEE), Khartoum, Sudan, 2021, pp. 1-6.

Section III.B, "5G Core Network Functions": This academic paper describes the UDM as the function that "stores the long-term security credentials used in the authentication for the SUPI, subscription data, and profiles of the user." It also notes its role in providing services to AMF, SMF, and AUSF. DOI: 10.1109/ICCCEEE54232.2021.9621328.