AMF

Access and Mobility Management Function

The Access and Mobility Management Function (AMF) is a key network function in the 5G Core network that handles access control and mobility management for UEs. It serves as the single point of contact for UEs in the control plane.

AMF Overview

The AMF is responsible for managing the access and mobility aspects of UEs in the 5G system. It acts as the termination point for the N1 interface (UE-AMF) and the N2 interface (RAN-AMF).

Key AMF Functions

The AMF performs the following key functions:

• Registration Management: Handles UE registration, deregistration, and registration updates
• Connection Management: Manages the signaling connection between UE and network
• Mobility Management: Handles UE mobility within and between tracking areas
• Access Authentication and Authorization: Authenticates UEs and authorizes access to the network
• Security Context Management: Manages security contexts and keys
• NAS Signaling: Terminates NAS signaling from UEs
• Network Slice Selection: Selects appropriate network slices for UEs
• SMF Selection: Selects appropriate SMF for PDU sessions

AMF Interfaces

The AMF connects to other network functions through various interfaces:

AMF Services

In the service-based architecture, the AMF provides the following services:

• Namf_Communication: Communication service for other NFs to interact with AMF
• Namf_EventExposure: Event exposure service for subscribing to AMF events
• Namf_MT: Mobile Terminated service for MT SMS and location services
• Namf_Location: Location service for providing UE location information

Registration Management

The AMF handles various registration procedures:

• Initial Registration: When a UE first attaches to the network
• Mobility Registration Update: When a UE moves to a new tracking area
• Periodic Registration Update: Regular registration updates based on timer
• Emergency Registration: For emergency services access

Mobility Management

The AMF manages UE mobility through:

• Tracking Area Management: Managing tracking area lists and updates
• Handover Coordination: Coordinating handovers between base stations
• Idle Mode Mobility: Managing UE mobility in idle mode
• Connected Mode Mobility: Managing UE mobility in connected mode

Security Functions

The AMF performs several security-related functions:

• Authentication Coordination: Coordinates with AUSF for UE authentication
• Security Context Management: Manages security contexts and keys
• Security Mode Control: Initiates security mode procedures
• Key Derivation: Derives various security keys

Network Slicing Support

The AMF supports network slicing through:

• Slice Selection: Selects appropriate network slices for UEs
• Slice Authentication: Performs slice-specific authentication
• Slice Access Control: Controls access to network slices
• Slice-aware Mobility: Manages mobility considering slice constraints

Related Specifications

The AMF is specified in the following 3GPP documents:

• TS 23.501: System Architecture for the 5G System
• TS 23.502: Procedures for the 5G System
• TS 29.518: 5G System; Access and Mobility Management Services
• TS 24.501: Non-Access-Stratum (NAS) protocol for 5G System
• TS 38.413: NG Application Protocol (NGAP)