This document is applicable to safety-related electronic systems using for digital communication purposes a transmission system which was not necessarily designed for safety-related applications. For transmission systems where the risk of unauthorized access is not tolerable, the document defines the interface to the 79 applicable cybersecurity standards. Both safety-related equipment and non-safety-related equipment can be connected to the transmission system. This document gives the specific requirements needed to achieve safety-related communication between safety-related equipment connected to the transmission system, while the general system requirements including allocation of safety requirements and content of the safety case are defined in EN 50129. This document is not applicable to existing systems, which had already been accepted prior to the release of this document. However, so far as reasonably practicable, it is applicable to modifications and extensions to existing systems, subsystems and equipment. This document does not specify the transmission system, equipment connected to the transmission system, solutions (e.g. for interoperability), which kind of data are safety-related and which are not. A safety-related equipment connected through an open transmission system can be subjected to many different IT security threats, against which an overall program is defined, encompassing management, technical and operational aspects.