A basic principle for testing and certification of bus systems for transferring safety-relevant messages was first presented in 2000 by the HVBG electrical engineering committee. The basic testing principle specified in the current version [GS-ET-26] is the basis for the international pre-IEC 61784-3 standard. This standard defines the following error assumptions for such a network: corruption, repetition, interchanging, loss, delay, insertion, masquerading and invalid addressing of messages.A safety protocol must be able to handle all these errors via suitable measures, i.e. they must be detected according to the required safety category.

The message delay assumption is particularly relevant for Ethernet-based systems. The application of non-safety-certified infrastructure components such as switches or routers creates scope for message delays. Even time monitoring (watchdog) of arriving messages is not sufficient.