Content for  TS 23.501  Word version:  18.5.0

The 5G QoS model is based on QoS Flows. The 5G QoS model supports both QoS Flows that require guaranteed flow bit rate (GBR QoS Flows) and QoS Flows that do not require guaranteed flow bit rate (Non-GBR QoS Flows). The 5G QoS model also supports Reflective QoS (see clause 5.7.5). The QoS Flow is the finest granularity of QoS differentiation in the PDU Session. A QoS Flow ID (QFI) is used to identify a QoS Flow in the 5G System. User Plane traffic with the same QFI within a PDU Session receives the same traffic forwarding treatment (e.g. scheduling, admission threshold). The QFI is carried in an encapsulation header on N3 (and N9) i.e. without any changes to the e2e packet header. QFI shall be used for all PDU Session Types. The QFI shall be unique within a PDU Session. The QFI may be dynamically assigned or may be equal to the 5QI (see clause 5.7.2.1). Within the 5GS, a QoS Flow is controlled by the SMF and may be preconfigured, or established via the PDU Session Establishment procedure (see clause 4.3.2 of TS 23.502), or the PDU Session Modification procedure (see clause 4.3.3 of TS 23.502). Any QoS Flow is characterised by:

• A QoS profile provided by the SMF to the AN via the AMF over the N2 reference point or preconfigured in the AN;
• One or more QoS rule(s) and optionally QoS Flow level QoS parameters (as specified in TS 24.501) associated with these QoS rule(s) which can be provided by the SMF to the UE via the AMF over the N1 reference point and/or derived by the UE by applying Reflective QoS control; and
• One or more UL and DL PDR(s) provided by the SMF to the UPF.

Within the 5GS, a QoS Flow associated with the default QoS rule is required to be established for a PDU Session and remains established throughout the lifetime of the PDU Session. This QoS Flow should be a Non-GBR QoS Flow (further details are described in clause 5.7.2.7). A QoS Flow is associated with QoS requirements as specified by QoS parameters and QoS characteristics. A QoS Flow may be enabled with PDU Set based QoS handling as described in clause 5.37.5. For such QoS Flows, PDU Set QoS Parameters (see clause 5.7.7) are determined by the PCF and provided by SMF to the NG-RAN as part of the QoS profile.

A QoS Flow may either be 'GBR' or 'Non-GBR' depending on its QoS profile. The QoS profile of a QoS Flow is sent to the (R)AN and it contains QoS parameters as described below (details of QoS parameters are described in clause 5.7.2):

• For each QoS Flow, the QoS profile shall include the QoS parameters:
  • 5G QoS Identifier (5QI); and
  • Allocation and Retention Priority (ARP).
• For each QoS Flow, the QoS profile may also include the QoS parameters:
  • PDU Set QoS Parameters (described in clause 5.7.7).
• For each Non-GBR QoS Flow only, the QoS profile may also include the QoS parameter:
  • Reflective QoS Attribute (RQA).
• For each GBR QoS Flow only, the QoS profile shall also include the QoS parameters:
  • Guaranteed Flow Bit Rate (GFBR) - UL and DL; and
  • Maximum Flow Bit Rate (MFBR) - UL and DL; and
• In the case of a GBR QoS Flow only, the QoS profile may also include one or more of the QoS parameters:
  • Notification control;
  • Maximum Packet Loss Rate - UL and DL.

Each QoS profile has one corresponding QoS Flow identifier (QFI) which is not included in the QoS profile itself. The usage of a dynamically assigned 5QI for a QoS Flow requires in addition the signalling of the complete 5G QoS characteristics (described in clause 5.7.3) as part of the QoS profile. When a standardized or pre-configured 5QI is used for a QoS Flow, some of the 5G QoS characteristics may be signalled as part of the QoS profile (as described in clause 5.7.3).

The Alternative QoS Profile(s) can be optionally provided for a GBR QoS Flow with Notification control enabled. If the corresponding PCC rule contains the related information (as described in TS 23.503), the SMF shall provide, in addition to the QoS profile, a prioritized list of Alternative QoS Profile(s) to the NG-RAN. If the SMF provides a new prioritized list of Alternative QoS Profile(s) to the NG-RAN (if the corresponding PCC rule information changes), the NG-RAN shall replace any previously stored list with it. An Alternative QoS Profile represents a combination of QoS parameters PDB, PER, Averaging Window and GFBR to which the application traffic is able to adapt. For a GBR QoS Flow using the Delay-critical resource type, an Alternative QoS Profile may also include the QoS parameter MDBV. For the NG-RAN determination whether the GFBR, the PDB and the PER can be fulfilled (i.e. for all Notification control scenarios described in clause 5.7.2.4), the NG-RAN shall also apply the value of the optional QoS parameter present in an Alternative QoS Profile instead of the corresponding QoS parameter's value in the QoS Profile (which is either provided explicitly or implicitly via the standardized 5QI QoS characteristics defined in clause 5.7.4) for every optional QoS parameter present in an Alternative QoS Profile (e.g. MDBV). When the NG-RAN sends a notification to the SMF that the QoS profile is not fulfilled, the NG-RAN shall, if the currently fulfilled values match an Alternative QoS Profile, include also the reference to the Alternative QoS Profile to indicate the QoS that the NG-RAN currently fulfils (see clause 5.7.2.4). The NG-RAN shall enable the SMF to determine when an NG-RAN node supports the Alternative QoS Profile feature but cannot fulfil even the least preferred Alternative QoS Profile.

The following options are supported to control QoS Flows:

1. For Non-GBR QoS Flows, and when standardized 5QIs or pre-configured 5QIs are used and when the 5QI is within the range of the QFI (i.e. a value less than 64), the 5QI value may be used as the QFI of the QoS Flow.
   1. A default ARP shall be pre-configured in the AN; or
   2. The ARP and the QFI shall be sent to RAN over N2 at PDU Session Establishment or at PDU Session Modification and when NG-RAN is used every time the User Plane of the PDU Session is activated; and
2. For all other cases (including GBR and Non-GBR QoS Flows), a dynamically assigned QFI shall be used. The 5QI value may be a standardized, pre-configured or dynamically assigned. The QoS profile and the QFI of a QoS Flow shall be provided to the (R)AN over N2 at PDU Session Establishment/Modification and when NG-RAN is used every time the User Plane of the PDU Session is activated.

Only options 1b and 2 may apply to 3GPP ANs. Options 1a, 1b and 2 may apply to Non-3GPP access.

The UE performs the classification and marking of UL User plane traffic, i.e. the association of UL traffic to QoS Flows, based on QoS rules. These QoS rules may be explicitly provided to the UE (i.e. explicitly signalled QoS rules using the PDU Session Establishment/Modification procedure), pre-configured in the UE or implicitly derived by the UE by applying Reflective QoS (see clause 5.7.5). A QoS rule contains the QFI of the associated QoS Flow, a Packet Filter Set (see clause 5.7.6) and a precedence value (see clause 5.7.1.9). An explicitly signalled QoS rule contains a QoS rule identifier which is unique within the PDU Session and is generated by SMF. There can be more than one QoS rule associated with the same QoS Flow (i.e. with the same QFI). When the UE informs the network about the number of supported Packet Filters for signalled QoS rules for the PDU Session (during the PDU Session Establishment procedure or using the PDU Session Modification procedure as described in clause 5.17.2.2.2 after the first inter-system change from EPS to 5GS for a PDU Session established in EPS and transferred from EPS with N26 interface), the SMF shall ensure that the sum of the Packet Filters used by all signalled QoS rules for a PDU Session does not exceed the number indicated by the UE. A default QoS rule is required to be sent to the UE for every PDU Session establishment and it is associated with a QoS Flow. For IP type PDU Session or Ethernet type PDU Session, the default QoS rule is the only QoS rule of a PDU Session which may contain a Packet Filter Set that allows all UL packets, and in this case, the highest precedence value shall be used for the QoS rule. For Unstructured type PDU Session, the default QoS rule does not contain a Packet Filter Set, and in this case the default QoS rule defines the treatment of all packets in the PDU Session. As long as the default QoS rule does not contain a Packet Filter Set or contains a Packet Filter Set that allows all UL packets, Reflective QoS should not be applied for the QoS Flow which the default QoS rule is associated with and the RQA should not be sent for this QoS Flow.

The SMF performs the binding of PCC rules to QoS Flows based on the QoS and service requirements (as defined in TS 23.503). The SMF assigns the QFI for a new QoS Flow and derives its QoS profile, corresponding UPF instructions and QoS Rule(s) from the PCC rule(s) bound to the QoS Flow and other information provided by the PCF. When applicable, the SMF provides the following information for the QoS Flow to the (R)AN:

• QFI;
• QoS profile as described in clause 5.7.1.2.
• optionally, Alternative QoS Profile(s) as described in clause 5.7.1.2a;

For each PCC rule bound to a QoS Flow, the SMF provides the following information to the UPF enabling classification, bandwidth enforcement and marking of User Plane traffic (the details are described in clause 5.8):

• a DL PDR containing the DL part of the SDF template;
• an UL PDR containing the UL part of the SDF template;
• the PDR precedence value (see clause 5.7.1.9) for both PDRs is set to the precedence value of the PCC rule;
• QoS related information (e.g. MBR for an SDF, GFBR and MFBR for a GBR QoS Flow) as described in clause 5.8.2;
• the corresponding packet marking information (e.g. the QFI, the transport level packet marking value (e.g. the DSCP value of the outer IP header);
• optionally, the Reflective QoS Indication is included in the QER associated with the DL PDR (as described in clause 5.7.5.3).

For each PCC rule bound to a QoS Flow, when applicable, the SMF generates an explicitly signalled QoS rule (see clause 5.7.1.4) according to the following principles and provides it to the UE together with an add operation:

• A unique (for the PDU Session) QoS rule identifier is assigned;
• The QFI in the QoS rule is set to the QFI of the QoS Flow to which the PCC rule is bound;
• The Packet Filter Set of the QoS rule is generated from the UL SDF filters and optionally the DL SDF filters of the PCC rule (but only from those SDF filters that have an indication for being signalled to the UE, as defined in TS 23.503);
• The QoS rule precedence value is set to the precedence value of the PCC rule for which the QoS rule is generated;
• for a dynamically assigned QFI, the QoS Flow level QoS parameters (e.g. 5QI, GFBR, MFBR, Averaging Window, see TS 24.501) are signalled to UE in addition to the QoS rule(s) associated to the QoS Flow. The QoS Flow level QoS parameters of an existing QoS Flow may be updated based on the MBR and GBR information received in the PCC rule (MBR and GBR per SDF are however not provided to UE over N1 in the case of more than one SDF) or, if the PCF has not indicated differently, when Notification control or handover related signalling indicates that the QoS parameter the NG-RAN is currently fulfilling for the QoS Flow have changed (see clause 5.7.2.4).

Changes in the binding of PCC rules to QoS Flows as well as changes in the PCC rules or other information provided by the PCF can require QoS Flow changes which the SMF has to provide to (R)AN, UPF and/or UE. In the case of changes in the explicitly signalled QoS rules associated to a QoS Flow, the SMF provides the explicitly signalled QoS rules and their operation (i.e. add/modify/delete) to the UE. The principle for classification and marking of User Plane traffic and mapping of QoS Flows to AN resources is illustrated in Figure 5.7.1.5-1.

In DL, incoming data packets are classified by the UPF based on the Packet Filter Sets of the DL PDRs in the order of their precedence (without initiating additional N4 signalling). The UPF conveys the classification of the User Plane traffic belonging to a QoS Flow through an N3 (and N9) User Plane marking using a QFI. The AN binds QoS Flows to AN resources (i.e. Data Radio Bearers of in the case of 3GPP RAN). There is no strict 1:1 relation between QoS Flows and AN resources. It is up to the AN to establish the necessary AN resources that QoS Flows can be mapped to, and to release them. The AN shall indicate to the SMF when the AN resources onto which a QoS Flow is mapped are released. If no matching DL PDR is found, the UPF shall discard the DL data packet. In UL:

• For a PDU Session of Type IP or Ethernet, the UE evaluates UL packets against the UL Packet Filters in the Packet Filter Set in the QoS rules based on the precedence value of QoS rules in increasing order until a matching QoS rule (i.e. whose Packet Filter matches the UL packet) is found.
• If no matching QoS rule is found, the UE shall discard the UL data packet.
• For a PDU Session of Type Unstructured, the default QoS rule does not contain a Packet Filter Set and allows all UL packets.
  The UE uses the QFI in the corresponding matching QoS rule to bind the UL packet to a QoS Flow. The UE then binds QoS Flows to AN resources.

The following characteristics apply for processing of DL traffic:

• UPF maps User Plane traffic to QoS Flows based on the PDRs.
• UPF performs Session-AMBR enforcement as specified in clause 5.7.1.8 and performs counting of packets for charging.
• UPF transmits the PDUs of the PDU Session in a single tunnel between 5GC and (R)AN, the UPF includes the QFI in the encapsulation header. In addition, UPF may include an indication for Reflective QoS activation in the encapsulation header.
• UPF performs transport level packet marking in DL on a per QoS Flow basis. The UPF uses the transport level packet marking value provided by the SMF (as described in clause 5.8.2.7).
• (R)AN maps PDUs from QoS Flows to access-specific resources based on the QFI and the associated 5G QoS profile, also taking into account the N3 tunnel associated with the DL packet.
• If Reflective QoS applies, the UE creates a new derived QoS rule as defined in clause 5.7.5.2.

Following characteristics apply for processing of UL traffic:

• UE uses the stored QoS rules to determine mapping between UL User Plane traffic and QoS Flows. UE marks the UL PDU with the QFI of the QoS rule containing the matching Packet Filter and transmits the UL PDUs using the corresponding access specific resource for the QoS Flow based on the mapping provided by (R)AN. For NG-RAN, the UL behaviour is specified in clause 10.5.2 of TS 38.300.
• (R)AN transmits the PDUs over N3 tunnel towards UPF. When passing an UL packet from (R)AN to CN, the (R)AN includes the QFI value, in the encapsulation header of the UL PDU, and selects the N3 tunnel.
• (R)AN performs transport level packet marking in the UL on a per QoS Flow basis with a transport level packet marking value that is determined based on the 5QI, the Priority Level (if explicitly signalled) and the ARP priority level of the associated QoS Flow.
• UPF verifies whether QFIs in the UL PDUs are aligned with the QoS Rules provided to the UE or implicitly derived by the UE in the case of Reflective QoS).
• UPF and UE perform Session-AMBR enforcement as specified in clause 5.7.1.8 and the UPF performs counting of packets for charging.

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). For HR-SBO PDU Sessions, if the DL Session AMBR for Offloading is provided as described (see clause 6.7 of TS 23.548), the DL Session AMBR for Offloading is enforced by UPF that supports the UL Classifier/Branching Point functionality in the VPLMN and additionally separately in every PSA UPF that terminates the N6 interface toward the local part of DN in the VPLMN. 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.

The QoS rule precedence value and the PDR precedence value determine the order in which a QoS rule or a PDR, respectively, shall be evaluated. The evaluation of the QoS rules or PDRs is performed in increasing order of their precedence value.

If a supporting NG-RAN receives for a UE a UE-Slice-MBR (see clause 5.7.2.6) for an S-NSSAI from the AMF, the NG-RAN shall apply this UE-Slice-MBR for all PDU Sessions of that UE corresponding to the S-NSSAI which have an active user plane if feasible. In particular, the NG-RAN shall enforce this UE-Slice-MBR as follows:

1. Whenever a request for a GBR QoS Flow establishment or modification is received, the NG-RAN admission control shall ensure that the sum of the GFBR values of the admitted GBR QoS Flows is not exceeding the UE-Slice-MBR and, if the QoS Flow cannot be admitted, the NG-RAN shall reject the establishment/modification of the QoS Flow.
2. The NG-RAN shall ensure that the aggregated bitrate across all GBR and Non-GBR QoS Flows belonging to those PDU Sessions is not exceeding the UE-Slice-MBR, while always guaranteeing the GFBR of every GBR QoS Flow of those PDU Sessions as described in clause 5.7.2.5.

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, 5QI Priority Level and ARP for the QoS Flow associated with the default QoS rule and highest Session-AMBR accepted by the VPLMN. 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. 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, 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.