3GPP 23.501 v20.2.0 — the document's own text
5.15.11.3.1 VPLMN NSAC Admission Mode
Taught in 17. One network, many networks (The 5G system architecture, in depth), 18. Being served by somebody else's network (The 5G system architecture, in depth), 6. One network behaving like several (The 5G system architecture, overview).
For NSAC of roaming UEs for maximum number of UEs per network slice and/or maximum number of PDU Sessions per network slice managed by the VPLMN, the following principles shall be used:
- For NSAC for the maximum number of UEs for S-NSSAI of the HPLMN, a NSACF in the VPLMN can be configured with the maximum number of allowed roaming UEs per mapped S-NSSAI of the HPLMN for a S-NSSAI of the HPLMN that is subject to NSAC. In such a case, the AMFs trigger a request to a NSACF of the VPLMN.
- For NSAC for the maximum number of PDU Sessions for S-NSSAI of the HPLMN, a NSACF in the VPLMN can be configured with the maximum number of allowed PDU Sessions in LBO mode per mapped S-NSSAI of the HPLMN for a S-NSSAI of the HPLMN that is subject to NSAC. In such a case, the anchor SMF in the VPLMN triggers a request to a NSACF of the VPLMN.
- For NSAC for the maximum number of UEs for S-NSSAI of the VPLMN, AMFs trigger a request to a NSACF of the VPLMN to perform NSAC based on the S-NSSAI of the VPLMN subject to NSAC. The NSACF of the HPLMN is not involved.
- For NSAC for the maximum number of PDU Sessions for S-NSSAI of the VPLMN in the LBO roaming case, the SMF triggers a request to a NSACF of the VPLMN to perform NSAC based on the S-NSSAI of the VPLMN subject to NSAC. The NSACF of the HPLMN is not involved.
‐ The AMF or SMF (in LBO roaming case) in the VPLMN provides both the S-NSSAI in the VPLMN and the corresponding mapped S-NSSAI in the HPLMN to the NSACF in the VPLMN. The NSACF in the VPLMN performs NSAC for both S-NSSAI of the VPLMN and the corresponding mapped S-NSSAI of the HPLMN based on the SLA between the VPLMN and the HPLMN.
In addition to configuring the VPLMN NFs with the maximum number of allowed roaming UEs per mapped S-NSSAI of the HPLMN subject to NSAC and the maximum number of allowed PDU Sessions in LBO mode per mapped S-NSSAI of the HPLMN subject to NSAC, the VPLMN can optionally fetch this information from the HPLMN primary NSACF in a hierarchal architecture or centralized NSACF in a centralized architecture. If the NSACF in VPLMN does not have quota configured but can receive quota from the HPLMN, the NSACF in VPLMN may interact with the HPLMN for retrieving the quota before processing any incoming request. The VPLMN is either configured or discovers the NSACF in the HPLMN for quota retrieval. However, in this case, the VPLMN rejects any additional requests exceeding the received information.