Abstract
Railway systems are composed of a multitude of subsystems, sensors, and actuators that exchange datagrams through safety-critical communication protocols. However, the vast majority of these protocols rely on ad hoc interlacing mechanisms and safety codes which raise the heterogeneity and complexity of the overarching railway system. Therefore, Rete Ferroviaria Italiana, the company who is in charge of managing the Italian railway network, coordinated the definition of the Protocollo Vitale Standard (Standard Vital Protocol). This protocol is inspired to, and compliant with, the communication protocols adopted for the European Train Control System (ETCS) (SUBSET, UNISIG, 037, Euroradio FIS, version 2.3. 0; SUBSET, UNISIG, 098, RBC-RBC safe communication interface, 2007), and it is meant to become the standard layer to enable safe communication between components of the Italian railway system. This paper reports our experience in the design, implementation, verification, and validation of the Protocollo Vitale Standard in compliance with the European safety standards for railway systems. We first defined a safety plan and a verification and validation plan, which guide the design, development, verification, and validation activities as required by safety standards. Guidelines of such plans have been followed strictly until completion of the work, which concludes with the provision of a safety case where all safety evidences are summarized. Noticeably, we (i) selected appropriate safety mechanisms, (ii) verified the software design, (iii) implemented the software in compliance with code metrics and coding rules, (iv) conducted tests to validate the protocol against its functional and performance requirements, and ultimately (v) devised all relevant documentation and a safety case which summarizes the evidences needed for certification.
Highlights
Safety-critical systems must adhere to appropriate guidelines to ensure that safety requirements are met
This paper reports our experience in the design, implementation, verification, and validation of the Protocollo Vitale Standard in compliance with the European safety standards for railway systems
Control systems and railway standards we report on control systems that are relevant for European railways, alongside with a summary of the CENELEC standards which provide prescriptive guidelines
Summary
Safety-critical systems must adhere to appropriate guidelines to ensure that safety requirements are met. Following the definition of safety, i.e., avoidance of catastrophic failures [1, 2], any misbehavior shall not lead to fatalities, severe injuries, or Bertieri et al Journal of the Brazilian Computer Society (2021) 27:5 major damages to the environment [3, 4]. A safety-critical system must be able to mitigate and manage potential catastrophic failures. Security breaches or vulnerabilities could lead to unsafe behaviors; safety-critical systems may be required to guarantee security, often with a particular accent on integrity of information. Safety standards typically define a safety integrity level (SIL) [5, 6], that sets qualitative and quantitative constraints that must be met to ensure the safe behavior of a target component or system. Matching the requirements of a desired safety integrity levels mean that a specific set of processes and techniques have been applied through the lifecycle of the system, and such application is documented by a specific list of work products
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