In this paper, we present the design of QoSMail, QoS email application demonstrating a flexible model for using simple declarative requirement-statements and awareness of system properties to dynamically select policies governing message delivery. We believe that these ideas may apply to other cases as well such as binding of stream interfaces. Foundations of the QoSmail design are a framework for describing Quality of Service requirements, a framework for describing the relevant attributes of the environment, i.e. the resources available for transport, and a framework for policy selection, based on QoS-requirements and environment attributes.
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