Wednesday, October 12, 2011

QoS Class Identifier (QCI)

The need for supporting a broader variety of applications requiring higher bandwidth and lower latency led 3GPP to alleviate the existing QoS principles with the introduction for EPS of a QoS Class Identifier (QCI).

The QCI is a scalar denoting a set of transport characteristics (bearer with/without guaranteed bit rate, priority, packet delay budget, packet error loss rate) and used to infer nodes specific parameters that control packet forwarding treatment (e.g., scheduling weights, admission thresholds, queue management thresholds, link-layer protocol configuration, etc.).

Each packet flow is mapped to a single QCI value (nine are defined in the Release 8 version of the specifications) according to the level of service required by the application. The usage of the QCI avoids the transmission of a full set of QoS-related parameters over the network interfaces and reduces the complexity of QoS negotiation.

The QCI, together with Allocation-Retention Priority (ARP) and, if applicable, Guaranteed Bit Rate (GBR) and Maximum Bit Rate (MBR), determines the QoS associated to an EPS bearer. A mapping between EPS and pre-Release 8 QoS parameters has been defined to allow proper interworking with legacy networks.

The QoS architecture in EPC enables a number of important capabilities for both operators and users:

  • VoIP support with IMS. QoS is a crucial element for providing LTE/IMS voice service. 
  • Enhanced application performance. Applications such as gaming or video can operate more reliably. 
  • More flexible business models. With flexible, policy-based charging control, operators and third-parties will be able to offer content in creative new ways. For example, an enhanced video stream to a user could be paid for by an advertiser. 
  • Congestion control. In congestion situations, certain traffic flows (e.g., bulk transfers, abusive users) can be throttled down to provide a better user experience for others.