Content for  TS 23.501  Word version:  18.0.0

Reflective QoS enables the UE to map UL User Plane traffic to QoS Flows without SMF provided QoS rules and it applies for IP PDU Session and Ethernet PDU Session. This is achieved by creating UE derived QoS rules in the UE based on the received DL traffic. It shall be possible to apply Reflective QoS and non-Reflective QoS concurrently within the same PDU Session. For a UE supporting Reflective QoS functionality, the UE shall create a UE derived QoS rule for the uplink traffic based on the received DL traffic if Reflective QoS function is used by the 5GC for some traffic flows. The UE shall use the UE derived QoS rules to determine mapping of UL traffic to QoS Flows. If the 3GPP UE supports Reflective QoS functionality, the UE should indicate support of Reflective QoS to the network (i.e. SMF) for every PDU Session. For PDU Sessions established in EPS and PDU Sessions transferred from EPS without N26 interface, the UE indicates Reflective QoS support using the PDU Session Establishment procedure. After the first inter-system change from EPS to 5GS for PDU Sessions established in EPS and transferred from EPS with N26 interface, the UE indicates Reflective QoS support using the PDU Session Modification procedure as described in clause 5.17.2.2.2. The UE as well as the network shall apply the information whether or not the UE indicated support of Reflective QoS throughout the lifetime of the PDU Session. Under exceptional circumstances, which are UE implementation dependent, the UE may decide to revoke previously indicated support for Reflective QoS using the PDU Session Modification procedure. In such a case, the UE shall delete all derived QoS rules for this PDU Session and the network shall stop any user plane enforcement actions related to Reflective QoS for this PDU Session. In addition, the network may provide signalled QoS rules for the SDFs for which Reflective QoS was used before. The UE shall not indicate support for Reflective QoS for this PDU Session for the remaining lifetime of the PDU Session. If under the same exceptional circumstances mentioned above and while NAS level MM or SM congestion control timer is running, the UE needs to revoke a previously indicated support for Reflective QoS, the UE performs PDU Session Release procedure that is exempt from MM and SM congestion control as defined in clause 5.19.7.

The UE derived QoS rule contains following parameters:

• One UL Packet Filter (in the Packet Filter Set as defined in clause 5.7.6);
• QFI;
• Precedence value (see clause 5.7.1.9).

Upon receiving DL packet, one UL Packet Filter derived from the received DL packet as described in this clause is used to identify a UE derived QoS rule within a PDU Session. For PDU Session of IP type, the UL Packet Filter is derived based on the received DL packet as follows:

• When Protocol ID / Next Header is set to TCP or UDP, by using the source and destination IP addresses, source and destination port numbers, and the Protocol ID / Next Header field itself.
• When Protocol ID / Next Header is set to UDP, if the received DL packet is UDP-encapsulated IPSec protected packet, by using the source and destination IP addresses, source and destination port numbers, the Security Parameter Index, and the Protocol ID / Next Header field itself. In this case, if an uplink IPSec SA corresponding to a downlink IPSec SA of the SPI in the DL packet exists and the SPI of the uplink IPSec SA is known to the NAS layer, then the UL Packet Filter contains an SPI of the uplink IPSec SA.
• When Protocol ID / Next Header is set to ESP, by using the source and destination IP addresses, the Security Parameter Index, and the Protocol ID / Next Header field itself. If the received DL packet is an IPSec protected packet, and an uplink IPSec SA corresponding to a downlink IPSec SA of the SPI in the DL packet exists and the SPI of the uplink IPSec SA is known to the NAS layer, then the UL Packet Filter contains an SPI of the uplink IPSec SA.

For PDU Session of Ethernet type the UL Packet Filter is derived based on the received DL packet by using the source and destination MAC addresses, the Ethertype on received DL packet is used as Ethertype for UL packet. In the case of presence of 802.1Q [98], the VID and PCP in IEEE Std 802.1Q [98] header(s) of the received DL packet is also used as the VID and PCP field for the UL Packet Filter. When double 802.1Q [98] tagging is used, only the outer (S-TAG) is taken into account for the UL Packet Filter derivation. The QFI of the UE derived QoS rule is set to the value received in the DL packet. When Reflective QoS is activated the precedence value for all UE derived QoS rules is set to a standardised value.

Reflective QoS is controlled on per-packet basis by using the Reflective QoS Indication (RQI) in the encapsulation header on N3 (and N9) reference point together with the QFI and together with a Reflective QoS Timer (RQ Timer) value that is either signalled to the UE upon PDU Session Establishment (or upon PDU Session Modification as described in clause 5.17.2.2.2) or set to a default value. The RQ Timer value provided by the core network is at the granularity of PDU Session (the details are specified in TS 24.501). When the 5GC determines that Reflective QoS has to be used for a specific SDF belonging to a QoS Flow, the SMF shall provide the RQA (Reflective QoS Attribute) within the QoS Flow's QoS profile to the NG-RAN on N2 reference point unless it has been done so before. When the RQA has been provided to the NG-RAN for a QoS Flow and the 5GC determines that the QoS Flow carries no more SDF for which Reflective QoS has to be used, the SMF should signal the removal of the RQA (Reflective QoS Attribute) from the QoS Flow's QoS profile to the NG-RAN on N2 reference point. When the 5GC determines to use Reflective QoS for a specific SDF, the SMF shall ensure that the UPF applies the RQI marking (e.g. by setting the indication to use Reflective QoS in the QER associated with the DL PDR if not already set) for this SDF. The SMF shall also ensure that the uplink packets for this SDF can be received by the UPF from the QoS Flow to which the DL PDR of the SDF is associated with as specified in TS 29.244, e.g. by generating a new UL PDR for this SDF for that QoS Flow and providing it to the UPF. When the UPF is instructed by the SMF to apply RQI marking, the UPF shall set the RQI in the encapsulation header on the N3 (or N9) reference point for every DL packet corresponding to this SDF. When an RQI is received by (R)AN in a DL packet on N3 reference point, the (R)AN shall indicate to the UE the QFI and the RQI of that DL packet. Upon reception of a DL packet with RQI:

• if a UE derived QoS rule with a Packet Filter corresponding to the DL packet does not already exist,
  • the UE shall create a new UE derived QoS rule with a Packet Filter corresponding to the DL packet (as described in clause 5.7.5.2); and
  • the UE shall start, for this UE derived QoS rule, a timer set to the RQ Timer value.
• otherwise,
  • the UE shall restart the timer associated to this UE derived QoS rule; and
  • if the QFI associated with the downlink packet is different from the QFI associated with the UE derived QoS rule, the UE shall update this UE derived QoS rule with the new QFI.

Upon timer expiry associated with a UE derived QoS rule the UE deletes the corresponding UE derived QoS rule. When the 5GC determines not to use Reflective QoS for a specific SDF any longer:

• The SMF shall ensure that the UPF stops applying RQI marking as specified in TS 29.244 (e.g. by removing the indication to use Reflective QoS from the QER associated with the DL PDR) for this SDF.
• When the UPF receives this instruction to stop applying RQI marking, the UPF shall no longer set the RQI in the encapsulation header on the N3 (or N9) reference point DL packets corresponding to this SDF.
• The SMF shall also ensure that, after an operator configurable time, the uplink packets for this SDF will not be accepted by the UPF over the QoS Flow on which Reflective QoS was applied for this SDF as specified in TS 29.244, e.g. by removing the UL PDR for this SDF from that QoS Flow.

When the 5GC determines to change the binding of the SDF while Reflective QoS is used for this SDF, the SMF shall ensure that the uplink packets for this SDF are accepted over the newly bound QoS Flow and, for an operator configurable time, over the previously bound QoS Flow.

The Packet Filter Set is used in the QoS rule and the PDR to identify one or more packet (IP or Ethernet) flow(s). The Packet Filter Set may contain one or more Packet Filter(s). Every Packet Filter is applicable for the DL direction, the UL direction or both directions. There are two types of Packet Filter Set, i.e. IP Packet Filter Set, and Ethernet Packet Filter Set, corresponding to those PDU Session Types.

For IP PDU Session Type, the Packet Filter Set shall support Packet Filters based on at least any combination of:

• Source/destination IP address or IPv6 prefix.
• Source / destination port number.
• Protocol ID of the protocol above IP/Next header type.
• Type of Service (TOS) (IPv4) / Traffic class (IPv6) and Mask.
• Flow Label (IPv6).
• Security parameter index.
• Packet Filter direction.

For Ethernet PDU Session Type, the Packet Filter Set shall support Packet Filters based on at least any combination of:

• Source/destination MAC address.
• Ethertype as defined in IEEE 802.3 [131].
• Customer-VLAN tag (C-TAG) and/or Service-VLAN tag (S-TAG) VID fields as defined in IEEE Std 802.1Q [98].
• Customer-VLAN tag (C-TAG) and/or Service-VLAN tag (S-TAG) PCP/DEI fields as defined in IEEE Std 802.1Q [98].
• IP Packet Filter Set, in the case that Ethertype indicates IPv4/IPv6 payload.
• Packet Filter direction.