DATA COMMUNICATION STRATEGIES AND CYBER SECURITY DEFENSES FOR A SAFETY RELATED DIGITAL CONTROL SYSTEM

摘要

Quality standards for systems important to safety require independence between safety systems and other systems. These control applications are designed such that credible failures in and consequential actions by other systems will not prevent the safety systems from performing their intended function and meeting regulatory requirements. Data communication systems must meet the reliability and availability goals assumed for the system and tolerate the effects of random transmission failures. One particular concern is that the transmission of multiple signals over a single path may constitute a single point of failure that may have a larger impact on plant safety than would occur in other systems. An important design principle for software of class IE systems is to ensure that the sequence of software processing executed for each expected situation can be deterministically established. It discourages the use of non-deterministic data, communications, and computations, as well as multitasking, dynamic scheduling, use of non-deterministic interrupts and event driven designs. It is also necessary to utilize a communication protocol that does not rely on acknowledgment by the receiver, in order to prevent a receiver from having influence on the sender's operation which can violate the design principle involving determinism. Likewise, the sender cannot influence the operation of the receiver. The receiver can only act on the data made available to it in accordance with the application design. Additionally, the security capabilities of a safety related digital control system should include both physical and logical access controls, safety to non-safety isolation, and control of the various life cycle activities. These are derived from key security concepts that include ensuring confidentiality, integrity, and availability. This paper discusses design criteria involving data communications for digital control systems as well as cyber security considerations, while demonstrating the capabilities in implementing these criteria using the TELEPERM® XS I&C system platform.