The performance of openSAFETY protocol via IEEE 802.11 wireless communication

Functional safety has become a crucial part of industrial automation. With industry environments being connected more than ever, achieving required functional safety depends on establishing safety-critical communication. Numerous application layer safety protocols have been developed to ensure compliance with functional safety standards for wired communications. However, with all the benefits wireless communications entails, wireless communication is pushing for an important place in the future of industrial automation. It is important that safety protocols also follow this transition and are able to operate as intended using a wireless channel. By default, openSAFETY frames are exchanged using UDP broadcast, whereas TCP provides additional reliability features. Thus, the aim of this paper is to analyze if safety-critical communication using a wireless channel can benefit from the additional reliability features provided by TCP. To answer this, we experimentally analyze the performance of openSAFETY protocol providing functional safety over the IEEE 802.11 standard for three different test cases. We analyze the performance in terms of median end-to-end delay and time spent by a safety node in a safe state for both protocol stacks. Results show that UDP provides lower median end-to-end delay, whereas TCP is able to achieve less time spent in a safe state under bounded delay constraint.