R.: Passive mid-stream monitoring of real-time properties

Passive monitoring or testing of complex systems and net-works running in the field can provide valuable insights into their behavior in actual environments of use. In certain contexts, such as network management and intrusion detec-tion for security, passive monitoring is the most applicable methodology for assuring correctness of the system’s behav-ior. More generally, it can serve to complement and extend functional testing and fault detection efforts that take place during the software/product development lifecycle. Two dis-tinguishing aspects of passive monitoring are that: (a) the fault detection process cannot influence the execution of the system by providing particular inputs to the system, and (b) observations are obtained mid-stream, from an unknown state in the middle of the execution of the system. In this paper, we present results on passively testing for real-time behavioral properties that can be applied to a large class of systems including those that can be modeled as timed automata. Our results provide a natural extension of the passive testing study conducted in [17] for untimed proper-ties. We have implemented our approach using the real-time model checker UPPAAL, and we report on its application to passively test fault tolerance software in a telecommuni-cations switch developed at Lucent Technologies