Measures of System Quality

This is a brief commentary on how measures of computer and communication system quality have evolved over the past 50 years. We take “quality” to be a generic term having various interpretations, the evolution of such being the central theme of the remarks that follow. The systems in question range from hardware and software components to global networks such as the Internet. We restrict our attention to measures that are probabilistic in nature, where their evaluation is based on system models (analytic, simulation, hybrid), actual systems, or some combination thereof. For the most part, however, our comments regarding evaluation are confined to modeling concerns.