NSSF

Technical Explanation

When a UE attempts to register with requested network slices (Requested NSSAI), the serving AMF queries the NSSF over the Nnssf Service-Based Interface. The NSSF evaluates the UE subscription from UDM, operator slicing policies, roaming agreements, and slice availability to determine the Allowed NSSAI, Configured NSSAI, and the target AMF set capable of serving those slices.

Key Functions

• Selecting the set of Network Slice instances serving the UE
• Determining the Allowed NSSAI and Configured NSSAI for the UE
• Selecting the candidate AMF set or redirecting registration to a dedicated AMF
• Determining the NRF to be used to discover Network Functions for the selected slices