Update Service Operation

The AMF uses this operation to update the NSSF with the supported S-NSSAI(s) on a per TA basis and to get informed of the S-NSSAIs available per TA (unrestricted) and the restricted S-NSSAI(s) per PLMN in that TA in the serving PLMN of the UE.

Figure 3-4 Update the S-NSSAIs the AMF supports per TA

• The NF service consumer (e.g. AMF) sends a HTTP PUT message to NSSF with NSSAI availability information, identifed by {nfId}, with NssaiAvalabilityInfo as body. Body of messgae contains a list of S-NSSAIs supported by AMF on a per TA basis.
• On receiving a PUT message, NSSF stores/updates the list in the session database.
• The NSSF authorizes the list based on NSSAI Auth rules and responds with the list of allowed SNSSAIs for that AMF on a per TAI basis as per the request.

Subscribe Service Operation

The Subscribe operation is used by AMF to subscribe to a notification of any changes in status of the NSSAI availability information (e.g. S-NSSAIs available per TA and the restricted S-NSSAI(s) per PLMN in that TA in the serving PLMN of the UE) upon this is updated by another AMF.

Figure 3-5 Create a Subscription

• AMF sends a POST request to NSSF with notification URL and a list of TAIs as JASON body.
• NSS stores the subscription request and responds with the list of allowed S-NSSAI/s per TAI for each TAI in the request. NSSF also returns a subscription-id and expiry (duration up to which NSSF ends notifications for any change in the status of Grant of S-NSSAI for subscribed TAI/s).

Unsubscribe Service Operation

The Unsubscribe operation is used by AMF to unsubscribe to a notification of any previously subscribed changes to the NSSAI availability information.

Figure 3-6 Unsubscribe a Subscription

• AMF sends a Delete request to NSSF with sunscription-id.
• NSSF checks for active subscription with the id and if found, deletes the subscription. NSSF responds with 204.

Notify Service Operation

The Notify service operation shall be used by the NSSF to update 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.

Figure 3-7 Update the AMF with any S-NSSAI restricted per TA

• NSSF sends notification to subscribed AMF when one or more following condition are true:
  • There is change at Grant rules on S-NSSAI corresponding to one or more of TAIs subscribed by AMF.
  • An S-NSSAI has been added or deleted for one or more of TAIs subscribed by AMF.

Delete Service Operation

The AMF uses this operation to delete the NSSAI Availability information stored for that AMF in the NSSF.

Figure 3-8 Delete the NSSAI Availability Information at NSSF

• The NF service consumer (e.g. AMF) sends a DELETE request to NSSF with {nfId}.
• The NSSF searches in session database for the NS-Availability data corresponding to nfId and deletes.