NSSF Overview

This section includes information about NSSF Installation in 5G environment.

Network Slice Selection Function (NSSF) selects the network slicing instance (NSI), determines the allowed network slice selection assistance information (NSSAI) and sets AMF to serve the UE. AMF can retrieve NRF, NSI ID, and target AMFs as part of UE initial registration and PDU establishment procedure.

Oracle NSSF interaction with NRF allows retrieving specific NF services to be used for the registration request. It also allows mechanism for registration and subsequent notification Function Instance Discovery.

The NSSF supports the following services:

Nnssf_NSSelection Service

Nnssf_NSSAIAvailability

Nnssf_NSSelection Service

This service is used by NF Service Consumer (AMF) to retrieve the information related to network slice. It also enables the NSSF to provide the AMF, the Allowed NSSAI and the Configured NSSAI for the Serving PLMN.

This service supports GET request during the following procedures by UE:

Initial Register: When the NSSF is able to detect authorized network slice information for the requested network slice selection information, the response body includes a payload body containing at least the allowed NSSAI, the target AMF Set or the list of candidate AMF(s).
PDU session establishment: This service allows the update of S-NSSAI(s), the NF service consumer support such as AMF on NSSF per TA basis to subscribe and notify any change in status of the SNSSAIs available per TA (unrestricted) and the restricted S-NSSAI(s) per PLMN in that TA in the serving PLMN of the UE.

Nnssf_NSSAIAvailability

NS-Availability service supports the following operations:

Update: AMF uses this feature to update the NSSF with the S-NSSAIs that AMF supports per TA basis.

NSSF authorizes the list based on NssaiAuth rules and responds with the list of the allowed S-NSSAI/s per TA, which the specific AMF is authorized to support.
Delete: The Delete service operation is used by the AMF to delete the NSSAI availability information stored for the NF service consumer in the NSSF.
Subscribe: The Subscribe operation is used by the AMF to subscribe the notification of any changes in the status of the NSSAI availability information, such as the S-NSSAIs available per TA and the restricted S-NSSAI(s) per PLMN in that TA in the serving PLMN of the UE.
Unsubscribe: The Unsubscribe operation is used by an NF Service Consumer (such as AMF) to unsubscribe the notification of any previously subscribed changes to the NSSAI availability information.
Notify: The Notify Service operation shall be used by the NSSF to update the NF Service Consumer (such as the AMF) with any change in status, on a per TA basis, of the S-NSSAIs available per TA (unrestricted) and the S-NSSAIs restricted per PLMN in that TA in the serving PLMN of the UE.