In this paper, we present a general framework for testing time-critical systems and software, as it is proposed in the European IST project MaTeLo. The main focus is on automatically generating a MCUM (Markov Chain Usage Model) starting from an FDT (Formal Description Technique) description in order to derive TTCN-3 (Testing and Test Control Notation version 3) compatible test case definitions.Our approach is a combination of statistical usage testing based on a given MCUM and specification-based testing that is using FDT inputs. Within MaTeLo, special attention is given to international standardized FDT notations, specifically ITU-T MSC (Message Sequence Chart). In addition, we make use of annotations to specify selected non-functional requirements to support the automated software testing of the real time systems. We also defined an XML-based representation format called MCML (Markov Chain Markup Language) to build a common interface between various parts of the MaTeLo tool set.