Perceived consistency

Quality of service guarantees for multimedia communication systems have been considered on several abstraction levels. In the multimedia networking field it is typical to identify the minimal QoS requirements of an application to save resources by guaranteeing its functionality. Many of these applications can operate in spite of an imperfect delivery of media data, while other applications such as distributed databases or distributed file systems consider perfect QoS necessary but accept delay. The basic problems of the latter is the consistency of their data, while the former require a consistent perception of the content. More generically, both QoS requirements can be interpreted as a problem of maintaining a consistent system state. Consequently we assume that many distributed applications, including most distributed multimedia applications, can fulfil their tasks in spite of imperfect consistency. Since the application requirements differ widely, the elements that make up "consistency" must be separated and classified. This paper introduces Consistency QoS and proposes a classification of elements that determine an application's consistency requirements. The low level QoS requirements that these separate parameters rely on are shown, and example parameter sets for application classes are given.