Security of Railway Control Systems and new information technologies

The new information technologies, such computer techniques, wireless (open) transmission standards and satellite systems applied for positioning have a important influence for different approach to safety criteria of railway control systems. The “fail-safe” rule assumed for relay control systems is based on high reliability of applied relays (guaranteed number of switches) and rigorous maintenance (homologation) procedure. The implementation of redundant, parallel computer systems has modified the concept of safety towards Tolerable Hazard Rate, where safety of computer systems is defined as an intensity of critical (dangerous, catastrophic) failures including self-testing. The wireless technologies respect the threats and their influence for functionality, availability and reliability of railway control systems (defined as probability).