1. Network Slice Selection Function (NSSF) Cloud Native User's Guide
  2. NSSF Supported Services
  3. NSSAI Availability Service

NSSAI Availability Service

The NSSAI Availability service is identified by the service operation name, Nnssf_NSSAIAvailability. For the Nnssf_NSSAIAvailability service the following service operations are defined:
  • Update Service Operation
  • Subscribe Service Operation
  • Unsubscribe Service Operation
  • Notify Service Operation
  • Delete Service Operation
  1. 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 4-4 Update the S-NSSAIs the AMF supports per TA

    img/update.png
    • The NF service consumer (Example: AMF) sends a HTTP PUT message to NSSF with NSSAI availability information, identified by {nfId}, with NssaiAvalabilityInfo as body. Body of message contains a list of S-NSSAIs supported by AMF on a per TA basis.
    • On receiving a PUT /PATCH message, NSSF stores/updates the list in the session database.
    • Supports HTTP PATCH for NS-Availability Update
    • The NSSF authorizes the list based on NSSAI Auth rules and responds with the list of allowed S-NSSAIs for that AMF on a per TAI basis as per the request.
  2. 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 (example: 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 4-5 Create a Subscription

    img/subscribe.png
    • 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).
  3. 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 4-6 Unsubscribe a Subscription

    img/unsubscribe.png
    • AMF sends a Delete request to NSSF with subscription-id.
    • NSSF checks for active subscription with the id and if found, deletes the subscription. NSSF responds with 204.
  4. Notify Service Operation
    The Notify service operation is 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 4-7 Update the AMF with any S-NSSAI restricted per TA

    img/notify.png
    • NSSF sends notification to subscribed AMF when one or more following conditions 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.
  5. Delete Service Operation

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

    Figure 4-8 Delete the NSSAI Availability Information at NSSF

    img/delete.png
    • The NF service consumer (example: 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.