Allowed NSSAI, Configured NSSAI, Requested NSSAI

Three NSSAI Types, Three Roles

The 5G system uses three related but distinct NSSAI concepts to manage slice access. Configured NSSAI is the set of S-NSSAIs provisioned on the UE's USIM by the operator, representing everything the subscriber is entitled to request. Requested NSSAI is the subset the UE actually sends in its Registration Request, reflecting which slices it needs right now. Allowed NSSAI is what the network returns in the Registration Accept message, which may be smaller than what was requested if some slices are unavailable or not authorized in the current serving area.