5G System Learning - AMF Status Indication

1. AMF (The Access and Mobility Management Function ) is a critical control plane element in 5G, responsible for managing user equipment (UE) access, mobility, and security within the 5G system. It handles initial UE registration and authentication, and manages handovers between network cells and access networks. The AMF collaborates with other network functions (such as the SMF) to establish and maintain data sessions for users.

2. The AMF's responsibilities are divided into the following areas:

• UE Registration and Authentication: The AMF authenticates the UE, verifies its identity and subscription credentials, and grants it access to 5G services.

• Mobility Management: Responsible for handling the complex process of moving a UE from one cell to another or between different radio access networks (NG-RANs).

• Context Management: Maintains the UE context, which includes information about the UE's current location, session state, and security.
• Interaction with Other Network Elements
• SMF (Session Management Function): The AMF collaborates with the SMF to establish, modify, and manage user data sessions.
• UDM (Unified Data Management): It communicates with the UDM to retrieve and manage user subscription information.      AUSF (Authentication Server Function): The AMF selects the appropriate AUSF to authenticate the UE's identity during registration.
• NSSF (Network Slice Selection Function): The AMF uses the NSSF to discover and select the appropriate network slice and functions based on the UE's location and requirements.
• Network Function Management: The AMF uses a service-based interface and the Network Repository Function (NRF) to discover and select other network functions.

3. The AMF Status Indication procedure is designed to support AMF management functions. This procedure uses non-UE-associated signaling and successful operation is shown in Figure 8.7.6.2-1 below, where:

• The AMF initiates this procedure by sending an "AMF Status Indication" message to the NG-RAN node.
• Upon receipt of the AMF Status Indication message, the NG-RAN node shall assume that the indicated GUAMI is unavailable and perform AMF reselection as defined in TS 23.501.
• If supported, the NG-RAN node shall take appropriate action as specified in TS 23.501 based on the existence of the timer method for the GUAMI removal IE.
• If the Backup AMF Name IE is included in the AMF Status Indication message, the NG-RAN node shall (if supported) perform AMF reselection according to the AMF indicated by the Backup AMF Name IE as specified in TS 23.501. If the Extended Backup AMF Name IE is included in the AMF Status Indication message, the NG-RAN node shall (if supported) perform AMF reselection according to the AMF indicated by the Extended Backup AMF Name IE as specified in TS 23.501.