5.30.2.7 Access to PLMN services via stand-alone non-public networks

To access PLMN services, a UE in SNPN access mode that has successfully registered with an SNPN may perform another registration via the SNPN User Plane with a PLMN (using the credentials of that PLMN) following the same architectural principles as specified in clause 4.2.8 (including the optional support for PDU Session continuity between PLMN and SNPN using the Handover of a PDU Session procedures in clauses 4.9.2.1 and 4.9.2.2 of TS 23.502 [3]) and the SNPN taking the role of "Untrusted non-3GPP access". Annex D, clause D.3 provides additional details.

NOTE: QoS differentiation in the SNPN can be provided on per-IPsec Child Security Association basis by using the UE or network requested PDU Session Modification procedure described in clause 4.3.3.2 of TS 23.502 [3]. In the PLMN, N3IWF determines the IPsec child SAs as defined in clause 4.12 of TS 23.502 [3]. The N3IWF is preconfigured by PLMN to allocate different IPsec child SAs for QoS Flows with different QoS profiles.

To support QoS differentiation in the SNPN with network-initiated QoS, the mapping rules between the SNPN and the PLMN are assumed to be governed by an SLA including: 1) mapping between the DSCP markings for the IPsec child SAs on NWu and the corresponding QoS, which is the QoS requirement of the PLMN and is expected to be provided by the SNPN and 2) N3IWF IP address(es) in the PLMN. The non-alteration of the DSCP field on NWu is also assumed to be governed by an SLA and by transport-level arrangements that are outside of 3GPP scope. The packet detection filters in the SNPN can be based on the N3IWF IP address and the DSCP markings on NWu.

To support QoS differentiation in the SNPN with UE-requested QoS, the UE can request for an IPsec SA the same 5QI from the SNPN as the 5QI provided by the PLMN. It is assumed that UE-requested QoS is used only when the 5QIs used by the PLMN are from the range of standardized 5QIs. The packet filters in the requested QoS rule can be based on the N3IWF IP address and the SPI associated with the IPsec SA.

Refer to clause D.7 for details on how to support QoS differentiation.

When the UE accesses the PLMN over NWu via a SNPN, the AMF in the serving PLMN shall send an indication toward the UE during the Registration procedure to indicate whether an IMS voice over PS session is supported or not.