5.7.1.11 QoS aspects of home-routed roaming

In the case of home-routed roaming, the V-SMF may apply VPLMN policies related with the SLA negotiated with the HPLMN or with QoS values supported by the VPLMN. Such policies may result in a situation that the V-SMF does not accept the PDU Session or does not accept some of the QoS Flows requested by the H-SMF.

QoS constraints represent the QoS that the VPLMN can accept for the QoS Flow associated with the default QoS rule and the PDU Session based on SLA or based on QoS values supported by the VPLMN. The QoS constraints may contain 5QI(s), 5QI Priority Level and ARP for the QoS Flow associated with the default QoS rule and highest Session-AMBR accepted by the VPLMN.

NOTE 1: For this Release of the specification, QoS constraints apply only to the non-GBR default QoS Flow.

NOTE 2: Additionally, at inter-PLMN scenarios, the VPLMN policies can result in re-mapping of QoS values of non-default QoS Flows e.g. in case the V-SMF receives an operator-specific 5QI value, whether/how the remapping is done is implementation specific according to the local policy and according to an inter-PLMN agreement between the involved operators.

NOTE 3: If remapping at inter-PLMN mobility between HPLMN and VPLMN is to be performed, the V-SMF chooses a 5QI value based on inter-PLMN agreement between the VPLMN and the HPLMN and updates the QoS Flows accordingly. The remapping can result in service degradation. At inter-PLMN mobility between two VPLMNs, the source V-SMF provides the 5QI values used in the source VPLMN to the target VPLMN. If the source VPLMN provides a 5QI value which is not part of the inter-PLMN agreement between the target VPLMN and the HPLMN, the target VPLMN can choose a 5QI value based on local policy and updates the QoS Flows accordingly using the procedure in clause 4.3.3.3 of TS 23.502 [3].

NOTE 4: If remapping at session management procedure in roaming case is to be performed, the V-SMF chooses a 5QI value based on inter-PLMN agreement between the VPLMN and the HPLMN and updates the QoS Flows accordingly. The remapping can result in service degradation.

NOTE 5: The VPLMN can provide multiple 5QI values, as constraints for the default QoS rule to HPLMN that can be accepted by VPLMN, based on inter-PLMN agreement. For other parameters (e.g. 5QI Priority level, ARP), the VPLMN provides the highest limit as constraint.

At PDU Session Establishment for home-routed roaming, to reduce the risk of PDU Session establishment failure due to QoS from the HPLMN not being compliant with SLA, the V-SMF may provide the VPLMN local policy in QoS constraints to the H-SMF as specified in clause 4.3.2.2.2 of TS 23.502 [3].

For intra-5GS mobility with V-SMF insertion or V-SMF change (e.g. inter-PLMN mobility), as specified in clause 4.23 of TS 23.502 [3], the new/target V-SMF may validate the currently applied QoS against the QoS constraints. The new/target V-SMF provides QoS constraints to the H-SMF during the mobility procedure. The new/target V-SMF may temporarily accept a higher QoS even if the currently applied QoS exceeds the QoS constraints. Alternatively, for the QoS parameters related with the QoS constraints, the V-SMF may locally downgrade these values before providing the corresponding QoS profiles to 5G AN. The V-SMF may decide to release the PDU Session if the HPLMN does not provide updated QoS compliant with the QoS constraints after the mobility procedure.

For IMS voice service (e.g. the IMS DNN defined by the GSMA), the V-SMF, based on local policy, may override the ARP received from HPLMN over N16 if the ARP indicates priority not in line with the local policy in VPLMN. The ARP override in the serving PLMN applies to both the QoS Flow associated with the default QoS rule and the QoS Flows for IMS voice, to apply the same allocation and retention priority for all users (i.e. roamers and non-roamers). For MPS (clause 5.16.5), the same allocation and retention priority is applied to all MPS service users (i.e. roamers and non-roamers), when roaming agreements are in place and where regulatory requirements apply.