EPIQ QoS Characterization Draft Version Jane W. S. Liu, Klara Nahrstedt, David Hull, Shigang Chen, and Baochun Li (Send comments to janeliu@cs.uiuc.edu) July 22, 1997 1 Introduction Researchers in diverse application domains have long advocated the use of flexible tasks as a way to make application systems adaptable to dynamic changes in user requirements and resource availability [1]. By task, we mean an application, or a component of the application system, that executes so it can deliver a service (or result) to some other system component(s) or the end-user. (Hereafter, we will use the terms service and result interchangeably.) Multiple hypothesis tracking, data compression/decompression, multimedia transmission and data retrieval are examples of tasks. A flexible task can trade the amounts of time and resources it requires to produce its result for the quality of the result it produces. In particular, a flexible task can produce a result of a degraded quality when it is necessary to conserve time and resources. For example, during an overload, a flexible tracking task can spend less time in correlating track records produced in the current scan with the established tracks from past scans, at the risk of producing more false and incorrect tracks. Tasks in numerical and statistical computations, real-time planning, diagnostic and decision support are usually designed to produce results of different quality when provided with different amounts of time, memory and information. Over the last decade, research on “flexible computation” in areas as diverse as signal processing, multi- media communication and display, visualization, query processing, and artificial intelligence has shown the approach to be effective and has produced the algorithms and methods needed to make the approach feasible. Systems employing the flexible computation approach gain the ability to trade the qualities of the services they produce for their time and resource consumptions. The EPIQ quality of service (QoS) management framework intends to provide the interfaces, mechanisms 1