A simple GSPN for modelling common mode failures in critical infrastructures

Abstract

It is now apparent that our nation's infrastructures and essential utilities have been optimized for reliability in benign operating environments. As such, they are susceptible to cascading failures induced by relatively minor events such weather phenomena, accidental damage to system components, and/or cyber attack. In contrast, survivable complex control structures should and could be designed to lose sizable portions of the system and still maintain essential control functions. This paper discusses the need for defining independent, survivable software control systems for automated regulation of critical infrastructures like electric power, telecommunications, and emergency communications systems. To exemplify the issue we describe an actual power blackout, and use that description to identify and analyze common mode faults leading to the cascading failure. We suspect that sources of common mode faults in real-time control systems are widespread and many, so we define modelling primitives that allow us to use generalized stochastic Petri nets (GSPN) for representing interdependency failures in very simple control systems. As such, this work provides the initial step toward creating a framework for modelling and analyzing reliability and survivability characteristics of critical infrastructures with both hardware and software controls.