AMF stands for Access and Mobility Management Function, which is a core network component in 5G. The AMF is responsible for managing access and mobility for 5G devices, and it interacts with other network functions such as the UPF (User Plane Function), SMF (Session Management Function), and AUSF (Authentication Server Function).
The AMF performs the following functions:
- Device registration: The AMF is responsible for registering a 5G device with the network and assigning it a unique identifier. This allows the network to keep track of the device and its location.
- Access management: The AMF performs access management functions such as authentication, authorization, and accounting (AAA) for 5G devices. It verifies the identity of the device and determines whether it is authorized to access the network.
- Mobility management: The AMF tracks the location of the device and manages handovers between cells and base stations. It ensures that the device maintains connectivity as it moves through different areas of the network.
- Policy enforcement: The AMF enforces network policies such as Quality of Service (QoS) and charging policies. It ensures that the network resources are allocated appropriately and that the device is charged correctly for the services it uses.
- Session management: The AMF manages the establishment, modification, and termination of 5G sessions for devices. It coordinates with other network functions such as the Session Management Function (SMF) to ensure that sessions are set up correctly and resources are allocated appropriately.
- User plane function (UPF) selection: The AMF selects the appropriate UPF based on network policies and the device’s location. The UPF is responsible for forwarding user data between the device and the network.
- Subscriber data management: The AMF stores and manages subscriber data such as the device’s profile, subscription data, and service data. This allows the network to provide personalized services to the device.
- Security management: The AMF is responsible for ensuring the security of 5G devices and the network. It manages security functions such as key management, authentication, and encryption.
- Network slicing: The AMF plays a critical role in network slicing, which allows the network to create virtualized network segments with dedicated resources and services for different use cases. The AMF is responsible for managing the access and mobility of devices within each network slice.
- Network integration: The AMF is responsible for integrating the 5G core network with external networks, such as 4G LTE networks or Wi-Fi networks. It coordinates with other network functions to ensure a seamless handover between different networks.
- Control plane management: The AMF manages the control plane of the 5G network, which is responsible for signalling and network management. It ensures that signalling messages are transmitted correctly between network functions and that the network resources are managed efficiently.
- Fault management: The AMF is responsible for detecting and managing faults within the 5G core network. It monitors the network for anomalies and alerts network operators if a fault is detected.
- Policy control: The AMF is responsible for enforcing policies related to network resource allocation, Quality of Service (QoS), and charging. It ensures that the policies are applied correctly and that the device is charged appropriately for the services it uses.
- Location management: The AMF is responsible for tracking the location of 5G devices and managing their mobility. It ensures that devices maintain connectivity as they move through different areas of the network.
- Network optimization: The AMF plays a key role in optimizing the 5G network for performance and efficiency. It monitors network usage and adapts the network resources to meet the demands of the devices.
AMF Role in NGAP (Next Generation Application Protocol)
- The AMF is a NGAP service user and provider in 5G.
- As a NGAP service user, the AMF sends NGAP messages to the RAN to manage the access and mobility of 5G devices.
- As a NGAP service provider, the AMF receives NGAP messages from the RAN.
- The AMF interacts with other network functions through the NGAP protocol, such as the gNB and SMF.
- The AMF uses NGAP messages to request resources, establish connections, initiate handovers, and manage the sessions of 5G devices.
- NGAP messages sent by the AMF include RAN setup request, RAN setup response, handover request, handover request acknowledgement, and path switch request.
- NGAP messages received by the AMF include UE context release request, UE context release command, and UE context release complete.
- The AMF is responsible for managing the mobility of 5G devices, such as performing location tracking and handovers between different gNBs.
- The AMF also manages the establishment and termination of sessions for 5G devices, coordinating with the SMF to ensure proper resource allocation and policy enforcement.
- The NGAP protocol is critical for enabling communication between the RAN and the 5G core network, with the AMF playing a key role in managing this communication.
NGAP message flows
List of AMF Services
Table 188.8.131.52-1 as per 3gpp
NAS Message Flow showing AMF involvement
The NAS message flows in 5G typically involve the following messages:
- Initial NAS message: The UE sends an initial NAS message, such as an Attach Request or Service Request, to the 5GC to initiate a session.
- Authentication and Security: The 5GC sends an Authentication Request message to the UE to authenticate the UE’s identity. The UE responds with an Authentication Response message, which includes a shared secret key. The 5GC then sends a Security Mode Command message to the UE, which contains security parameters to establish a secure connection.
- Registration: Once authentication and security are established, the UE sends a Registration Request message to the 5GC to register with the network. The 5GC responds with a Registration Accept message, which contains information about the assigned temporary identifier (GUTI) and other session parameters.
- Session management: During the session, the UE may initiate session management messages, such as a Service Request message to request a new service or a Session Modification Request message to modify an existing session.
- Detach: When the UE wishes to end the session, it sends a Detach Request message to the 5GC to detach from the network. The 5GC responds with a Detach Accept message, which confirms the detachment.