Performability Modeling: Back to the Future?

J. F. Meyer


After more than 30 years of work concerning its theory, techniques, tools, and applications, performability modeling is well understood by the many people who have been responsible for its development. During this period, other concepts have emerged which likewise aim to express how well a system performs (serves it users) under realistic operating conditions that include occurrences of both internal and external faults. The most prevalent of these are various concepts and measures of quality of service (QoS) and experience (QoE) which are "performability-like" in that they refer to aspects of both system performance (in the strict sense) and dependability. To make a more precise comparison with performability measures, it would be helpful to observe some basic properties of the latter which follow from the original modeling framework. In turn, differences revealed in this comparison could point to certain measure-formulation and model-solution problems that deserve further attention. Accordingly, the title of this talk is asking whether it's time to go back to first principles and, after doing so, suggest what needs to be done to facilitate future work on model-based QoS/QoE evaluation. Presuming a "yes" answer to this question, both avenues are followed in the talk.

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