This paper describes a software mechanism, called quality events, that utilizes application- and/or system-level service extensions to provide quality of service (QoS) guarantees to end users. Such extensions offer flexibility in: (1) how application- and/or system-level services are dynamically managed to maintain required quality, (2) when such management occurs, and (3) where this service management is performed. Several adaptive QoS management strategies are implemented with quality events and compared with respect to their ability to meet application-specific QoS requirements. These management strategies have different service adaptation latencies, and different degrees of coordination between services. Significant performance variations observed for these alternative strategies demonstrate the importance of a flexible QoS management mechanism like quality events. Finally, we show that adaptive QoS and, hence, resource management strategies can lead to more efficient use of resources, and better qualities of service for certain applications than non-adaptive resource management methods.
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