# Functional Safety Networks and Protocols in the Industrial Internet of Things Era
###### Abstract  
Functional safety networks are becoming of paramount importance in industrial systems, due to the progressive innovation introduced by the Industry 4.0 paradigm, characterized by high production flexibility, reliability and scalability. In this context, new and challenging applications have emerged such as hyperautomation, which refers to the combination of machine vision, robotics, communication, and learning, with the explicit involvement of humans. This requires the pervasive and ubiquitous connectivity encompassed by the Industrial Internet of Things, typically achieved via wireless systems. As an example, wireless communications are today fundamental to open up to new categories of autonomous devices that can actively collaborate with human personnel in the production process. This challenging scenario has important implications for safety. Indeed, a reliable coordination among sensors, actuators and computing systems is required to provide satisfactory levels of safety, especially in the case of innovative processes and technologies, such as mobile and collaborative robotics. Hence, it becomes imperative to ensure the correct transfer of safety-critical data via communication networks. In this paper, we address the challenges concerned with functional safety networks and protocols in Industrial Internet of Things ecosystems. We first introduce the design characteristics of functional safety networks and discuss the adoption of safety protocols over wireless networks. Then, we specifically address one of such protocols, namely Fail Safety over EtherCAT (FSoE), and provide the results of an extensive experimental session carried out exploiting a prototype system, implemented using commercial devices based on a WiFi network. Finally, the outcomes of the experiments are used as a basis for a discussion about future trends of functional safety in the Industrial Internet of Things era. functional safety networks; Industry 4.0; Industrial Internet of Things; industrial wireless networks IEEEexample:BSTcontrol-of-the-art, 2015  
2  
G.O.O. dedicated hardware circuits or electromechanical parts, will be replaced and effectively improved by Functional Safety Networks (FSNs), namely communication systems used for the transmission of safety-relevant messages, that are designed to implement distributed functional safety systems [3]. As a matter of fact, industrial automation systems have made extensive use of communication networks to connect their components deployed over (possibly large) distributed plant areas [4]. This trend started roughly at the beginning of the 1990s and progressively enforced over the years, thanks to the improvements achieved by such networks in terms of performance indicators, such as timeliness, reliability, dependability and scalability. Today, this scenario is further revolutionized by the adoption of the Industrial Internet of Things (IIoT) [5; 6] where a pervasive communication infrastructure allows connection of cloud systems, controllers, industrial equipment, sensors and actuators to dramatically improve the performance of manufacturing systems in terms of product quality, production efficiency, safety and security [7; 8]. From the architectural point of view, FSNs exploit functional safety protocols logically placed on top of the protocol stacks of wired industrial networks. This is the case, for instance, of the ProfiSafe protocol used in Profibus and Profinet, or of the Fail Safe over EtherCAT (FSoE) in EtherCAT systems. FSNs are expected to be ever more deployed and integrated in the factory communication infrastructures, so that plant safety data and information will become part of IIoT ecosystems and, as such, they will be accessed and elaborated using the new services and tools made available in such a context [9].