Modeling layered distributed communication systems

Today, component-based software and system development has gained considerable attention and is wide-spread. Components and/or modules manifest the well-proven engineering principle of divide and conquer. Formal approaches have helped to provide a theoretical foundation to component-orientation. There is a broad range of system architectures in practice today in terms of layered distributed open systems (as for example known in telecommunications). However, the mathematical formalisms developed so far are rarely applied to these practical architectures. In fact, the notion of distribution and stacked communication layers is hardly understood precisely and not supported by architecture description languages. This article addresses this gap. The formal conditions of distribution and layering are investigated and a mathematical model for layered distributed systems is presented. Communication refinement and so-called complex connectors turn out to be vital concepts which are not addressed in today's modeling languages. In addition to that, two important design approaches are derived for the architectural design of complex communication systems: A node-centric and a network-centric design approach. Both can significantly improve the design process.