3GPP 23.501 v20.2.0 — the document's own text
6.2.14 NSSF
Taught in 4. What each network function does (The 5G system architecture, in depth), 2. Who does what in the core (The 5G system architecture, overview).
The Network Slice Selection Function (NSSF) supports the following functionality:
- Selecting the set of Network Slice instances serving the UE;
- Determining the Allowed NSSAI and, if needed, the mapping to the Subscribed S-NSSAIs;
- Determining the Configured NSSAI and, if needed, the mapping to the Subscribed S-NSSAIs;
- Determining the AMF Set to be used to serve the UE, or, based on configuration, a list of candidate AMF(s), possibly by querying the NRF;
- The NSSF may provide support for Network Slice restriction and Network Slice instance restriction based on NWDAF analytics.
- Determining whether an S-NSSAI has to be replaced and providing to the AMF the indication that the S-NSSAI is unavailable and a corresponding Alternative S-NSSAI, e.g. based on received NWDAF analytics (e.g. for Service Experience for a Network Slice or Slice load level), or local trigger from the OAM system.