1. Network Slice Selection Function (NSSF) Cloud Native User's Guide
  2. Overview

3 Overview

This document provides information on how to use the Oracle Communications Network Slice Selection Function (OCNSSF) in the cloud native 5G core network.

Network slices enables the users to provide customized networks with different functionality (Example: mobility), performance requirements (Example: latency, availability, reliability etc). Network slices may differ for supported features and network function optimisations. In such cases, network slices may have different S-NSSAIs with different slice and service types. The user can deploy instances of multiple network slices delivering exactly the same features but for different groups of User Equipments (UE). As these instances deliver a different committed service because they are dedicated to a customer, in which case such network slices may have different S-NSSAIs with the same slice or service type but different slice differentiators. OCNSSF fulfills the requirement for determining the individual network function pertaining to a slice. This section includes information about the role of OCNSSF in the 5G Service based architecture.

Network Slice Selection Function is a functional element that supports the following functionalities:
  • OCNSSF enables the Access and Mobility Management Function (AMF) to perform initial registration and PDU session establishment.
  • OCNSSF uses an NF Service Consumer (AMF) to update the S-NSSAI(s) the AMF supports and notify any change in status.
  • OCNSSF selects the network slicing instance (NSI) and determines the authorized Network Slice Selection Assistance Information (NSSAIs) and AMF to serve the UE.
  • AMF can retrieve NRF, NSI ID, target AMFs as part of UE initial registration and PDU establishment procedure.
  • OCNSSF interaction with NRF allows retrieving specific NF services to be used for registration request.

NSSF is responsible for providing the following information as and when queried by the AMF:

  • Allowed NSSAIs
  • Configured NSSAIs
  • Restricted NSSAIs
  • Candidate AMF List (in case of registration)
  • Network Slice instance ID (for PDU registration)
  • Slice-level NRF information (for PDU Connectivity)

OCNSSF supports the above functions through the following NSSF services:

  • Network Slice Selection service (Nnssf_NSSelection): This service is used by an NF Service Consumer (AMF) to retrieve the information related to network slice. Network Slice Selection Service enables Network Slice selection in the serving Home Public Land Mobile Network (HPLMN).
  • NS-Availability Service (Nnssf_NSAvailability): This service is used by an NF Service Consumer (AMF) to update the S-NSSAI(s) the AMF supports on a per TA basis on the NSSF. Also to notify any change in status, on a per TA basis, of the SNSSAIs available per TA (unrestricted) and the restricted SNSSAI(s) per PLMN in that TA in the serving PLMN of the UE.