Nowadays, Industrial Control Systems (ICSs) are employed to monitor and control safety-critical industrial processes. A Supervisory Control and Data Acquisition (SCADA) system is an ICS to perform centralized monitoring and also to control field sites in long-distance communication networks. A SCADA is a distributed system composed of several Remote Terminal Units (RTUs) and a Master Terminal Unit (MTU). RTUs interface with field sensors, local control devices, and field actuators, and the MTU gathers data from RTUs, provides an operator interface to display information, and controls remote sites. RTUs are typically connected to the MTU through a client/server network. Since RTUs operate commonly in a harsh industrial environment, fault tolerance is a key requirement, especially for safety-critical industrial processes. Studies show that a significant number of transient faults caused by a harsh environment lead to control flow errors in the RTU’s processors. A control flow checking technique, called PLC-CFC, has been proposed to detect control flow errors in several RTUs in a SCADA system. The proposed technique can be applied to all ICSs which employ microcontrollers, microprocessors, PLCs, or personal computers as their RTUs. The proposed technique has been experimentally evaluated on a real ICS consists of some PLC devices and a main server. For experimental evaluation, 30,000 faults were injected on distributed system and the PLC-CFC technique detected more than 96.76% of the injected faults. The performance and the memory overheads of the technique are about 18.12% and 16.17% on average, respectively.

Keywords