Class-based quality of service (CBQoS) is the ability of a network to provide improved services to identified classes of network traffic. These services include supporting dedicated bandwidth, improving loss characteristics, managing network congestion, traffic shaping and setting traffic priorities. CBQoS involves two major components, traffic classes, and traffic policies.
In the classification of network traffic, a traffic descriptor categorizes a packet as belonging to a group or class. By classifying network traffic, you can divide it into multiple priority levels or classes of service. Traffic classes are created using the class-map command which maps protocols and applications to a particular class.
A traffic policy provides the mapping between the classes and the network controls used to provide the traffic priority, bandwidth guarantee, traffic shaping and other services available to traffic classes. Traffic policies are created using the policy-map command and are assigned to a particular interface using the service-policy command.