Section: 4.7.3 Bearer level QoS parameters
Content: The EPS bearer QoS profile includes the parameters QCI, ARP, GBR and MBR, described in this clause. This clause also describes QoS parameters which are applied to an aggregated set of EPS Bearers: APN-AMBR and UE-AMBR. Each EPS bearer (GBR and Non-GBR) is associated with the following bearer level QoS parameters: - QoS Class Identifier (QCI); - Allocation and Retention Priority (ARP). A QCI is a scalar that is used as a reference to access node-specific parameters that control bearer level packet forwarding treatment (e.g. scheduling weights, admission thresholds, queue management thresholds, link layer protocol configuration, etc.), and that have been pre-configured by the operator owning the access node (e.g. eNodeB). A one-to-one mapping of standardized QCI values to standardized characteristics is captured in TS 23.203[ Policy and charging control architecture ]  [6]. NOTE 1: On the radio interface and on S1, each PDU (e.g. RLC PDU or GTP-U PDU) is indirectly associated with one QCI via the bearer identifier carried in the PDU header. The same applies to the S5 and S8 interfaces if they are based on GTP. NOTE 2: When required by operator policy, the eNodeB can be configured to also use the ARP priority level in addition to the QCI to control bearer level packet forwarding treatment in the eNodeB for SDFs having high priority ARPs. The ARP shall contain information about the priority level (scalar), the pre-emption capability (flag) and the pre-emption vulnerability (flag). The primary purpose of ARP is to decide whether a bearer establishment / modification request can be accepted or needs to be rejected due to resource limitations (typically available radio capacity for GBR bearers). The priority level information of the ARP is used for this decision to ensure that the request of the bearer with the higher priority level is preferred. In addition, the ARP can be used (e.g. by the eNodeB) to decide which bearer(s) to drop during exceptional resource limitations (e.g. at handover). The pre-emption capability information of the ARP defines whether a bearer with a lower ARP priority level should be dropped to free up the required resources. The pre-emption vulnerability information of the ARP defines whether a bearer is applicable for such dropping by a pre-emption capable bearer with a higher ARP priority level. Once a bearer has been successfully established, the packet handling (e.g. scheduling and rate control) within the eNodeB, PDN GW, and Serving GW should be solely determined by the following EPS bearer QoS parameters: QCI, GBR and MBR, and by the AMBR parameters. However, when required by operator policy, the eNodeB can be configured to also use a bearer's ARP priority level in addition to the QCI to determine the relative priority of the SDFs for packet handling (e.g. scheduling and rate control) in the eNodeB as defined in TS 23.203[ Policy and charging control architecture ]  [6] clause 6.1.7.2. This configuration applies only for bearers with high priority ARPs as defined in TS 23.203[ Policy and charging control architecture ]  [6] clause 6.1.7.3. The ARP priority level may be used in addition to the QCI to determine the transport level packet marking, e.g. to set the DiffServ Code Point. The ARP is not included within the EPS QoS Profile sent to the UE. NOTE 3: The ARP should be understood as "Priority of Allocation and Retention"; not as "Allocation, Retention, and Priority". NOTE 4: Video telephony is one use case where it may be beneficial to use EPS bearers with different ARP values for the same UE. In this use case an operator could map voice to one bearer with a higher ARP, and video to another bearer with a lower ARP. In a congestion situation (e.g. cell edge) the eNodeB can then drop the "video bearer" without affecting the "voice bearer". This would improve service continuity. NOTE 5: The ARP may also be used to free up capacity in exceptional situations, e.g. a disaster situation. In such a case the eNodeB may drop bearers with a lower ARP priority level to free up capacity if the pre-emption vulnerability information allows this. Each GBR bearer is additionally associated with the following bearer level QoS parameters: - Guaranteed Bit Rate (GBR); - Maximum Bit Rate (MBR). The GBR denotes the bit rate that can be expected to be provided by a GBR bearer. The MBR limits the bit rate that can be expected to be provided by a GBR bearer (e.g. excess traffic may get discarded by a rate shaping function). See clause 4.7.4 for further details on GBR and MBR. GBR bearers are not supported by NB-IoT. The PDN GW uses the RAT Type to ensure that GBR bearers are not active when the UE is using NB-IoT. Each APN access, by a UE, is associated with the following QoS parameter: - per APN Aggregate Maximum Bit Rate (APN-AMBR). The subscribed APN-AMBR is a subscription parameter stored per APN in the HSS, which applies as APN-AMBR unless the APN-AMBR is modified by the MME (e.g in roaming scenarios and/or for usage of NB-IoT) or the PDN GW, based on local policy (e.g. for RAT Type = NB-IoT) or PCRF interactions. The APN-AMBR limits the aggregate bit rate that can be expected to be provided across all Non-GBR bearers and across all PDN connections of the same APN (e.g. excess traffic may get discarded by a rate shaping function). Each of those Non-GBR bearers could potentially utilize the entire APN-AMBR, e.g. when the other Non-GBR bearers do not carry any traffic. GBR bearers are outside the scope of APN-AMBR. The P-GW enforces the APN-AMBR in downlink. Enforcement of APN-AMBR in uplink is done in the UE and additionally in the P-GW. NOTE 6: All simultaneous active PDN connections of a UE that are associated with the same APN shall be provided by the same PDN GW (see clauses 4.3.8.1 and 5.10.1). APN-AMBR applies to all PDN connections of an APN. For the case of multiple PDN connections of an APN, if a change of APN-AMBR occurs due to local policy or the PDN GW is provided the updated APN-AMBR for each PDN connection from the MME or PCRF, the PDN GW initiates explicit signalling for each PDN connection to update the APN-AMBR value. Each UE in state EMM-REGISTERED is associated with the following bearer aggregate level QoS parameter: - per UE Aggregate Maximum Bit Rate (UE-AMBR). The UE-AMBR is limited by a subscription parameter stored in the HSS. The MME shall set the UE-AMBR to the sum of the APN-AMBR of all active APNs up to the value of the subscribed UE-AMBR. The UE-AMBR limits the aggregate bit rate that can be expected to be provided across all Non-GBR bearers of a UE (e.g. excess traffic may get discarded by a rate shaping function). Each of those Non-GBR bearers could potentially utilize the entire UE-AMBR, e.g. when the other Non-GBR bearers do not carry any traffic. GBR bearers are outside the scope of UE AMBR. The E-UTRAN enforces the UE-AMBR in uplink and downlink except for PDN connections using the Control Plane CIoT EPS Optimisation. The GBR and MBR denote bit rates of traffic per bearer while UE-AMBR/APN-AMBR denote bit rates of traffic per group of bearers. Each of those QoS parameters has an uplink and a downlink component. On S1_MME the values of the GBR, MBR, and AMBR refer to the bit stream excluding the GTP-U/IP header overhead of the tunnel on S1_U. The HSS defines, for each PDN subscription context, the 'EPS subscribed QoS profile' which contains the bearer level QoS parameter values for the default bearer (QCI and ARP) and the subscribed APN-AMBR value. The subscribed ARP shall be used to set the priority level of the EPS bearer parameter ARP for the default bearer while the pre-emption capability and the pre-emption vulnerability information for the default bearer are set based on MME operator policy. In addition, the subscribed ARP shall be applied by the P-GW for setting the ARP priority level of all dedicated EPS bearers of the same PDN connection unless a different ARP priority level setting is required (due to P-GW configuration or interaction with the PCRF). NOTE 7: The ARP parameter of the EPS bearer can be modified by the P-GW (e.g. based on interaction with the PCRF due to e.g. MPS user initiated session) to assign the appropriate pre-emption capability and the pre-emption vulnerability setting. The ARP pre-emption vulnerability of the default bearer should be set appropriately to minimize the risk of unnecessary release of the default bearer.