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Cyclic Redundancy Check (CRC) is an approved coding method for error detection. It ensures a low probability of undetected errors, i.e. a low residual error probability, and is easy to implement. In industrial fieldbus systems, communication is usually executed through different layers. Each layer may have its specific check such that a nesting of checks exists. At present, this nesting is not included in the safety proof of systems. Hence, additional effort is made to achieve the required degree of safety which was probably on hand but could not be proven. The paper presents a method to involve the nesting in the calculation of the residual error probability by means of stochastic automata. This method helps to reduce the number of worst case assumptions in the overall safety proof and finally to reduce the necessary on-line efforts like the number of parity bits.
Date of Conference: 21-23 May 2008