AMF
Access and Mobility Management Function: the 5GC control-plane function handling registration, connection, mobility management, and NAS protocol termination from UEs.
The AMF is the first 5G core function a phone really talks to. After the radio side sets up an NGAP association, the gNB relays the UE's NAS messages to a chosen AMF, and from then on the AMF owns that subscriber's control-plane context — registration state, reachability, the security context after authentication, and which slices the UE is allowed onto.
It deliberately does not handle the data path or session details. When the UE wants connectivity, the AMF picks an SMF and forwards the session request; the SMF does the heavy lifting. Mobility is the AMF's other big job: it tracks the UE across TAIs, drives paging when something needs to reach an idle device, and coordinates handovers it can't leave entirely to the RAN. On the SBA it exposes Namf services that other NFs call to communicate with, or page, a given UE.
Frequently asked questions
- What is the difference between the AMF and the LTE MME?
- The MME in 4G did almost everything on the control plane — mobility, NAS, and session/bearer management all in one box. 5G split that. The AMF keeps the access and mobility half (registration, connection management, NAS, paging), while session management moved out to the SMF. So one MME function roughly maps to AMF + SMF, and that separation is what lets you scale and deploy them independently.
- Does the AMF terminate NAS signalling?
- Yes for the mobility management NAS (registration, service request, authentication). Session management NAS is generated by the SMF but tunnelled transparently through the AMF, which forwards it without interpreting the contents.
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