Abstract
This paper explores aspects concerning system-level specification, modeling and simulation of real-time embedded systems. By means of case studies, we investigate how object-oriented methodologies, and in particular UML, support the modeling of industrial scale real-time systems, and how different architectures can be explored by model simulation.We are mainly interested in the problem of system specification as it appears from the prospect of the whole design process. The discussion is illustrated by a large system model from the telecommunications area, the GSM base transceiver station.