(1) Any operation that allows traffic priorities to be designated. Through quality of service, different traffic throughout a network can be classified and administered.
(2) In OSI, a value that specifies certain performance characteristics of a service, session, or link. In OSI Communications Subsystem, quality of service is provided at the network layer.
(3) For an asynchronous transfer mode (ATM) virtual channel or a Networking BroadBand Services (NBBS) network connection, a set of communication characteristics such as end-to-end delay, jitter, and packet loss ratio.
(4) A set of communication characteristics required by an application. QoS defines a specific transmission priority, level of route reliability, and security level.
(5) A measure of system performance and system availability.