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In this article we describe the QoS concept of the evolved packet system, which was standardized in 3GPP Release 8. The concept provides access network operators and service operators with a set of tools to enable service and subscriber differentiation. Such tools are becoming increasingly important as operators are moving from a single to a multi-service offering at the same time as both the number of mobile broadband subscribers and the traffic volume per subscriber is rapidly increasing. The "bearer" is a central element of the EPS QoS concept and is the level of granularity for bearer-level QoS control. The network-initiated QoS control paradigm specified in EPS is a set of signaling procedures for managing bearers and controlling their QoS assigned by the network. The EPS QoS concept is class-based, where each bearer is assigned one and only one QoS class identifier by the network. The QCI is a scalar that is used within the access network as a reference to node-specific parameters that control packet forwarding treatment. This class-based approach, together with the network-initiated QoS control paradigm, gives network operators full control over the QoS provided for its offered services for each of its subscriber groups.