there are seven NextGen core NFs, namely, (1) AMF, (2) Session Management Function (SMF), (3) Policy Control Function (PCF), (4) Application Function (AF), (5) Authentication Server Function (AUSF), (6) User Plane Function (UPF), and (7) User Data Management (UDM).
The 5G Session Management Function (SMF) is a Fundamental element of the 5G Service-Based Architecture (SBA). The SMF is primarily responsible for interacting with the decoupled data plane, creating updating and removing Protocol Data Unit (PDU) sessions and managing session context with the User Plane Function (UPF).
Application Protocol (NGAP) to carry Non Access Stratum (NAS) messages across the N1 or N2 reference interfaces in order to request a new session. The Access and Mobility Management Function (AMF) receives these requests and handles anything to do with connection or mobility management while forwarding session management requirements over the N11 interface to the SMF. The AMF determines which SMF is best suited to handle the connection request by querying the Network Repository Function (NRF). That interface and the N11 interface between the AMF and the specific SMF assigned by the NRF, use the Service Based Interface (SBI) message bus, to which all Service-Base Application elements are connected. The SBI message bus employs RESTful API principles over HTTP/2 -- web technologies that dramatically simplify and accelerate service deployments.