QoS Class Identifier

QoS Class Identifier (QCI) is a mechanism used in 3GPP Long Term Evolution (LTE) networks to ensure carrier traffic is allocated appropriate Quality of Service (QoS). Different carrier traffic requires different QoS and therefore different QCI values. QCI value 9 is typically used for the default carrier of a UE/PDN for non privileged subscribers.

Background
To ensure that carrier traffic in LTE networks is appropriately handled, a mechanism is needed to classify the different types of carriers into different classes, with each class having appropriate QoS parameters for the traffic type. Examples of the QoS parameters include Guaranteed Bit Rate (GBR) or non-Guaranteed Bit Rate (non-GBR), Priority Handling, Packet Delay Budget and Packet Error Loss rate. This overall mechanism is called QCI.

Mechanism
The QoS concept as used in LTE networks is class-based, where each carrier type is assigned one QoS Class Identifier (QCI) by the network. The QCI is a scalar that is used within the access network (namely the eNodeB) as a reference to node specific parameters that control packet forwarding treatment, for example scheduling weight, admission thresholds and link-layer protocol configuration.

The QCI is also mapped to transport network layer parameters in the relevant Evolved Packet Core (EPC) core network nodes (for example, the PDN Gateway (P-GW), Mobility Management Entity (MME) and Policy and Charging Rules Function (PCRF)), by preconfigured QCI to Differentiated Services Code Point (DSCP) mapping.

According to 3GPP TS 23.203, 9 QCI values in Rel-8 (13 QCIs Rel-12, 15 QCIs Rel-14) are standardized and associated with QCI characteristics in terms of packet forwarding treatment that the carrier traffic receives edge-to-edge between the UE and the P-GW. Scheduling priority, resource type, packet delay budget and packet error loss rate are the set of characteristics defined by the 3GPP standard and they should be understood as guidelines for the pre-configuration of node specific parameters to ensure that applications/services mapped to a given QCI receive the same level of QoS in multi-vendor environments as well as in roaming scenarios. The QCI characteristics are not signalled on any interface.

The following table illustrates the standardized characteristics as defined in the 3GPP TS 23.203 standard "Policy and Charging Control Architecture".

Every QCI (GBR and Non-GBR) is associated with a Priority level. Priority level 0.5 is the highest Priority level. If congestion is encountered, the lowest Priority level traffic (highest Priority number!) would be the first to be discarded.

QCI-65, QCI-66, QCI-69 and QCI-70 were introduced in 3GPP TS 23.203 Rel-12.

QCI-75 and QCI-79 were introduced in 3GPP TS 23.203 Rel-14.

QCI-67 was introduced in 3GPP TS 23.203 Rel-15.