5.32.4 QoS Support

The 5G QoS model for the Single-Access PDU Session is also applied to the MA PDU Session, i.e. the QoS Flow is the finest granularity of QoS differentiation in the MA PDU Session. One difference compared to the Single-Access PDU Session is that in a MA PDU Session there can be separate user-plane tunnels between the AN and the PSA, each one associated with a different access. However, the QoS Flow is not associated with specific access, i.e. it is access agnostic, so the same QoS is supported when the traffic is distributed over 3GPP and non-3GPP accesses. The SMF shall provide the same QFI in 3GPP and non-3GPP accesses so that the same QoS is supported in both accesses.

A QoS Flow of the MA PDU Session may be either Non-GBR or GBR depending on its QoS profile.

For a Non-GBR QoS Flow, the SMF provides a QoS profile to both 5G-ANs during MA PDU Session Establishment or MA PDU Session Modification procedure:

• During MA PDU Session Establishment procedure, the QoS profile to both ANs if the UE is registered over both accesses.
• During MA PDU Session Modification procedure, the QoS profile is provided to the 5G-AN(s) over which the user plane resources are activated.

For a GBR QoS Flow, the SMF shall provide a QoS profile to 5G-AN(s) as follows:

• If the PCC rule allows a GBR QoS Flow in a single access, the SMF provides the QoS profile for the GBR QoS Flow to the access network allowed by the PCC rule.
• If the PCC rule allows a GBR QoS Flow in both accesses and the Steering Mode is different from Redundant, the SMF decides to which access network to provide the QoS profile for the GBR QoS Flow based on its local policy (e.g. the access where the traffic is ongoing according to the Multi Access Routing rule).
• If the PCC rule allows a GBR QoS Flow in both accesses and the Steering Mode is Redundant, the SMF provides the QoS profile for the GBR QoS Flow to both access networks. Whenever the SMF recognizes that resources are not allocated in one access network, the SMF shall notify the PCF about the resource allocation failure and indicate the respective Access Type. Whenever the SMF recognizes that resources are not allocated in both access networks, the SMF shall release the resources for the GBR QoS Flow and report to the PCF about the removal of the PCC rule.

NOTE 1: The SMF knows about the allocation of resources in an access network from the interaction with the access network during GBR QoS Flow establishment/modification as well as during the release of resources by the access network.

For a GBR QoS Flow, traffic splitting is not supported. If the UPF determines that it cannot send GBR traffic over the current ongoing access e.g. based on the N4 rules and access availability and unavailability report from the UE as described in clause 5.32.5.3, the UPF shall send an Access Availability report to the SMF.

Based on the Access Availability report and if the Steering Mode is different from Redundant, the SMF decides whether to move GBR QoS Flows to the other access when one access is not available:

• if the PCC rule allows the GBR QoS Flows only on this access, the SMF shall release the resources for the GBR QoS Flow and report to the PCF about the removal of the PCC rule.
• if the corresponding PCC rule allows the GBR QoS Flow on both accesses and the other access is not available, the SMF shall release the resources for the GBR QoS Flow and report to the PCF about the removal of the PCC rule.
• if the PCC rule allows the GBR QoS Flow on both accesses and the other access is available, the SMF shall try to move the GBR QoS Flow to the other access. The SMF may trigger a PDU session modification procedure to provide the QoS profile to the other access and release the resources for the GBR QoS Flow in the current access.
• if Notification Control parameter is not included in the PCC rule for the GBR QoS Flow and the other access does not accept the QoS profile, the SMF shall release the resources for the GBR QoS Flow and report to the PCF about the removal of the PCC rule.
• if the Notification Control parameter is included in the PCC rule, the SMF shall notify the PCF that GFBR can no longer be guaranteed. After the other access accepts the QoS profile, the SMF shall notify the PCF that GFBR can again be guaranteed. If the other access does not accept the QoS profile, the SMF shall delete the GBR QoS Flow and report to the PCF about the removal of the PCC rule.

NOTE 2: The ATSSS rule for GBR QoS Flow only allows the UE to steer traffic over a single access so that the network knows in which access the UE sends GBR traffic. If the network wants to move GBR QoS Flow to the other access, the network needs to update ATSSS rule of the UE.

Based on the Access Availability report and if the Steering Mode is Redundant, the SMF behaves as follows:

• if both accesses are not available, the SMF shall release the resources for the GBR QoS Flow and report to the PCF about the removal of the PCC rule.

NOTE 3: The UPF can detect that both accesses are not available based on implementation specific means.

• when one of the accesses becomes unavailable while the other access is still available, the SMF shall neither release the resources for the GBR QoS Flow nor notify the PCF that GFBR can no longer be guaranteed (if the Notification Control parameter is included in the PCC rule).

NOTE 4: The access network will typically release the resources for a GBR QoS Flow if there is no traffic transferred for a certain amount of time and this will then trigger the SMF notification to PCF described above.

When the MA PDU Session is established or when the MA PDU Session is modified, the SMF may provide QoS rule(s) to the UE via one access, which are applied by the UE as specified in clause 5.7.1.4. The QoS rule(s) provided by SMF via one access are commonly used for both 3GPP access and non-3GPP access, so the QoS classification is independent of ATSSS rules.

The derived QoS rule generated by Reflective QoS is applied independently of the access on which the RQI was received. When any of the MPTCP functionality, MPQUIC-UDP functionality or the MPQUIC-IP functionality is used in the UE, the UE shall use the IP address/prefix of the MA PDU Session and the final destination address to generate the derived QoS rule.

When any of the MPTCP functionality, MPQUIC-UDP functionality or MPQUIC-IP functionality is enabled for the MA PDU Session:

• any QoS rules or PDRs that apply to the MA PDU Session IP address/prefix and port also apply (a) to the MPTCP "link-specific multipath" IP addresses/prefixes and ports used by the UE to establish MPTCP subflows over 3GPP and non-3GPP accesses and (b) to the "MPQUIC link-specific multipath" IP addresses/prefixes and ports used by the UE to transmit UDP/IP flows over 3GPP and non-3GPP accesses; and
• any QoS rules or PDRs that apply to the IP address/prefix and port of the final destination server in DN also apply (a) to the IP address and port of the MPTCP proxy for corresponding MPTCP subflows that are terminated at the proxy; and (b) to the IP address and port of the MPQUIC proxy for corresponding UDP/IP flows that are terminated at the proxy.

When the MPQUIC-E functionality is enabled for the MA PDU Session:

• any QoS rules or PDRs that apply to the source MAC address for the MA PDU Session of Ethernet type also apply to the "MPQUIC link-specific multipath" IP addresses/prefixes and ports used by the UE to transmit Ethernet flows over 3GPP and non-3GPP accesses.
• any QoS rules or PDRs that apply to the destination MAC address of the server in DN for the MA PDU Session of Ethernet type also apply to the IP address and port of the MPQUIC proxy for corresponding Ethernet flows that are terminated at the proxy.

NOTE 5: How these associations are made when the MPTCP functionality, MPQUIC-UDP functionality, MPQUIC-IP functionality or MPQUIC-E functionality is enabled for the MA PDU session is left up to the UE and UPF implementations.