Modelling of Hazards Effect on Safety Integrity of Open Transmission Systems

Abstract

The paper is concerned with safety appraisal of safety-related communication systems (SRComSs) with open transmission system, where except in addition to message transmission integrity also confidentiality is recommended to be provided. The authors focused on safety analysis of safety-related messages transmission secured using cryptographic and safety code mechanisms and on the possibilities of modelling safety-related industrial communication system, where a high safety integrity level SIL3 is required to be guaranteed. The paper features mathematical procedures to calculate the rate of hazardous transmission failure of safety-related messages in the result of electromagnetic interference (EMI) effects in the communication channel and by the presence of random hardware failures of SRComS. The theoretical techniques and safety analyses emerge from risk analysis and are compared with the knowledge gained by the authors during safety verifications of such systems for transportation applications. It is a little explored area, because the standards concerning safety-related control systems (SRCSs) did not support any cryptography-based methods. A quantitative safety integrity analysis of SRComS is based on utilisation of Markov's processes. The proposed Markov's model is applied on an open transmission system built on the IEEE 802.11g standard, which is complemented by cryptographic and safety code. The calculations are performed using Mathematica software tool. The proposed base model is universal and can be modified (simplified) in dependence on the parameters of a specific SRComS.