Quality Class Indicators (QCI)

"LTE supports different types of services including web browsing, video streaming, VoIP, online gaming, real-time video, etc., with standardized quality class indicators (QCI) [1]. Each QCI defines a set of requirements for quality of service (QoS) bearers, e.g., maximum tolerable delay, packet loss rate and/or guaranteed bit-rate (GBR). A GBR bearer allows to define a minimum bit-rate and a maximum bit-rate (MBR) to be allocated to a particular UE." an excerpt from [2].

Best Effort Scenario: All UEs are non-GBR with QCI equal to 9.

According to [1]: 
QoS class identifier (QCI): A scalar that is used as a reference to a specific packet forwarding behaviour (e.g. packet loss rate, packet delay budget) to be provided to a  Service Data Flow (SDF). This may be implemented in the access network by the QCI referencing node specific parameters that control packet forwarding treatment (e.g. scheduling weights, admission thresholds, queue management thresholds, link layer protocol configuration, etc.), that have been pre-configured by the operator at a specific node(s) (e.g. eNodeB). 




Services using a GBR QCI and sending at a rate smaller than or equal to GBR can in general assume that congestion related packet drops will not occur, and 98 percent of the packets shall not experience a delay exceeding the QCI's PDB.

Services using a Non-GBR QCI should be prepared to experience congestion related packet drops, and 98 percent of the packets that have not been dropped due to congestion should not experience a delay exceeding the QCI's PDB.

The Packet Error Loss Rate (PELR) defines an upper bound for the rate of SDUs (e.g. IP packets) that have been processed by the sender of a link layer protocol (e.g. RLC in E-UTRAN) but that are not successfully delivered by the corresponding receiver to the upper layer (e.g. PDCP in E-UTRAN). Thus, the PELR defines an upper bound for a rate of non congestion related packet losses.

In general, the rate of congestion related packet drops can not be controlled precisely for Non-GBR traffic. This rate is mainly determined by the current Non-GBR traffic load, the UE's current radio channel quality, and the configuration of user plane packet processing functions (e.g. scheduling, queue management, and rate shaping). 

An operator would choose GBR QCIs for services where the preferred user experience is "service blocking over service dropping", i.e. rather block a service request than risk degraded performance of an already admitted service request. 


References
[1] 3GPP, “Policy and charging control architecture,” TS 23.203, v10.7.0, 2012.
[2] Cicalo, Sergio, et al. "Improving QoE and Fairness in HTTP Adaptive Streaming over LTE Network." (2015).