This paper describes a distributed quality of service (QoS) management architecture and middleware that accommodates and manages different dimensions and measures of QoS. The middleware supports the specification, maintenance and adaptation of end-to-end QoS (including temporal requirements) provided by the individual components in complex real-time application systems. Using QoS negotiation, the middleware determines the quality levels and resource allocations of the application components. A prototype was implemented to demonstrate its practicality. The paper also discusses how protocol parameters are determined in our architecture and what their performance implications are.