5.15.11.3.2 VPLMN with HPLMN assistance NSAC Admission

In this admission mode HPLMN delegates NSAC for S-NSSAIs subject to NSAC to the VPLMN, both for number of registered UEs and the number of LBO PDU sessions.

Every NSACF performing admission in the VPLMN for each S-NSSAI of the HPLMN that is subject to NSAC and mapped to a corresponding S-NSSAI of the VPLMN, fetches from the VPLMN primary NSACF in a hierarchal architecture the maximum number of registered UEs to be admitted and/or the maximum number of LBO PDU sessions to be allowed. The VPLMN primary or central NSACF, in turn, acquires the information from the HPLMN central or primary NSACF depending on the deployed architecture. The VPLMN is either configured or discovers the NSACF in the HPLMN for quota retrieval.

If re-distribution of quota is required in the VPLMN in a hierarchal architecture, amongst multiple NSACFs than this is handled by the primary NSACF in VPLMN with no involvement from the HPLMN. The VPLMN NSACF discovers the HPLMN primary or central NSACF or be configured with the needed information.

For any request(s) received in any NSACF in the VPLMN exceeding the received maximum number information, the NSACF interacts with the VPLMN primary NSACF which in turn interacts with HPLMN primary or central NSACF to receive an updated roaming quota for the corresponding mapped S-NSSAI, which is used to determine whether admission request is accepted or rejected, unless forbidden by the SLA. If an admission request is accepted, the UE entry is stored in the NSACF performing admission in the VPLMN. This applies to the number of registered UEs as well as the number of LBO PDU sessions. The primary NSACF in VPLMN may re-distribute the received updated roaming quota to the NSACFs in VPLMN to perform NSAC for Roaming UEs according to the principles described in clauses 5.15.11.1 and 5.15.11.2.