This paper describes an architecture that provides support for quality of service (QoS) specification and enforcement in heterogeneous distributed computing systems. The Quartz QoS architecture has been designed to overcome various limitations of previous QoS architectures that have constrained their use in heterogeneous systems. These limitations include dependencies on specific platforms and the fact that their functionality is often limited by design to one particular area of application. Quartz is able to accommodate differences among diverse computing platforms and areas of application by adopting a flexible and extensible platform-independent design, which allows its internal components to be rearranged dynamically in order to adapt the architecture to the surrounding environment. Further significant problems found in other QoS architectures, such as the lack of flexibility and expressiveness in the specification of QoS requirements and limited support for resource adaptation, are also addressed by Quartz. This paper describes the motivations for and design of Quartz in detail, presents a prototype implementation of Quartz, evaluates its design based on experience with a number of applications that use this prototype, and finally compares Quartz to a number of other QoS architectures.

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