(1) A classification assigned to users of a telephony network that gives them particular rights and privileges. In an internal telephone system, it can include the ability to make international calls or dial 900 numbers. In the public telephone network, it is used for tariffs and differentiates between categories such as residential or commercial, flat rate or message units, private line or party line.

(2) In an enterprise network, class of service (CoS) differentiates high-priority traffic from lower-priority traffic. Tags may be added to the packets to identify such classes, but they do not guarantee delivery as do quality of service (QoS) functions, which are implemented in the network devices. See QoS.