Introduction

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 operators to provide customized networks with different functionality (e.g. mobility), performance requirements (e.g. latency, availability, reliability...etc.). Network slices may differ for supported features and network functions optimisations, in which case such Network Slices may have e.g. different S-NSSAIs with different Slice/Service Types. The operator can deploy multiple Network Slice instances delivering exactly the same features but for different groups of UEs, e.g. as they deliver a different committed service and/or because they are dedicated to a customer, in which case such Network Slices may have e.g. different S-NSSAIs with the same Slice/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 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).
NSSAI Availability Service, Nnssf_NSSAIAvailability. 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 and 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.