Section: 5.7.1.8 AMBR/MFBR enforcement and rate limitation
Content: UL and DL Session-AMBR (see clause 5.7.2.6) shall be enforced by the UPF, if the UPF receives the Session-AMBR values from the SMF as described in clause 5.8.2.7 and clause 5.8.5.4. For UL Classifier PDU Sessions, UL and DL Session-AMBR (see clause 5.7.2.6) shall be enforced in the SMF selected UPF that supports the UL Classifier functionality. In addition, the DL Session-AMBR shall be enforced separately in every UPF that terminates the N6 interface (i.e. without requiring interaction between the UPFs) (see clause 5.6.4). For multi-homed PDU Sessions, UL and DL Session-AMBR shall be enforced in the UPF that supports the Branching Point functionality. In addition, the DL Session-AMBR shall be enforced separately in every UPF that terminates the N6 interface (i.e. without requiring interaction between the UPFs) (see clause 5.6.4). NOTE: The DL Session-AMBR is enforced in every UPF terminating the N6 interface to reduce unnecessary transport of traffic which may be discarded by the UPF performing the UL Classifier/Branching Point functionality due to the amount of the DL traffic for the PDU Session exceeding the DL Session-AMBR. Discarding DL packets in the UL Classifier/Branching Point could cause erroneous PDU counting for support of charging The (R)AN shall enforce UE-AMBR (see clause 5.7.2.6) in UL and DL per UE for Non-GBR QoS Flows. The UE shall perform UL rate limitation on PDU Session basis for Non-GBR traffic using Session-AMBR, if the UE receives a Session-AMBR. MBR per SDF is mandatory for GBR QoS Flows but optional for Non-GBR QoS Flows. The MBR is enforced in the UPF. The MFBR is enforced in the UPF in the Downlink for GBR QoS Flows. The MFBR is enforced in the (R)AN in the Downlink and Uplink for GBR QoS Flows. For non-3GPP access, the UE should enforce MFBR in the Uplink for GBR QoS Flows. The QoS control for Unstructured PDUs is performed at the PDU Session level and in this Release of the specification there is only support for maximum of one 5G QoS Flow per PDU Session of Type Unstructured. When a PDU Session is set up for transferring unstructured PDUs, SMF provides the QFI which will be applied to any packet of the PDU Session to the UPF and UE.