# Functional Safety Networks and Protocols in the Industrial Internet of Things Era
## 5 Discussion and Future Perspectives  
The results of the experiments confirm the potential effectiveness of the black channel approach, as they demonstrate the possibility of implementing the FSoE protocol over WiFi and, more generally, over networks for which it was not explicitly designed, without any modification to the protocol itself. Compliance with the safety requirements imposed by SIL3 could not be demonstrated (actually, for the case of UDP as transport layer, it could not be achieved at all). However, the results obtained with TCP and \(UDP_{c}\) are really promising and pave the way to a wide range of applications. These achievements can likely be extended to other protocols that adopt the same approach, e.g., those defined by IEC 61784-3. Among them, ProfiSAFE seems a very suitable candidate, since such a protocol has some common features with FSoE (for example, the master-slave strategy as well as some of the countermeasures against communication impairments). Another safety protocol that could easily work over wireless networks is OPC UA Safety. In this case, the safety stack is implemented (via a suitable mapper sublayer) on top of the OPC UA protocol stack which, in turn, relies on the TCP/IP suite. Thus, the safety protocol is not aware of the underlying physical layer. In this respect, the assessment provided in [29] clearly shows that the use of different physical layers for OPC UA applications may actually have an impact on the performance, but the feasibility of such applications is ensured whatever being the adopted physical layer. Looking at future applications, 5G cellular networks may be profitably considered for functional safety. Indeed, they are envisaged to be an opportunity for IIoT ecosystems [30]. For example, a 5G-based industrial communication system is presented in [31], where a controller (master) exchanges data with sensors and actuators (slaves) in full-duplex mode. Within 5G, the Ultra-Reliable Low Latency Communication (URLLC) introduced specific features to achieve low latency and higher reliability [32], becoming an interesting candidate not only for typical industrial communication but also for functional safety networks. Both WiFi and 5G may considerably exploit the Time Sensitive Networking (TSN) set of standards [33], originally conceived for Ethernet networks. Actually, some aspects of TSN are remarkable towards the implementation of functional safety over wireless. Indeed, redundancy and deterministic communication, which are among the key features of TSN, allow to increase reliability as well as to ensure pre-determined reaction times. Security of industrial networks against cyber attacks [34] is a further important issue that may have a very dangerous impact on functional safety networks, especially when included in IIoT ecosystems. If adequate countermeasures are not undertaken, a threat can compromise the behavior of such networks and, hence, the safety of machinery, equipment and personnel. Unfortunately, most of the functional safety protocols have not \begin{table}
\begin{tabular}{l l} \hline \hline  & **SFNT\({}_{\text{FSoE}}\)** [μs] \\ \hline UDP & 293,128.30 \\ TCP & 475,480.00 \\ UDPc & 301,522.90 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: SFNT values for the three transport layers. built-in security countermeasures, since at the time they were designed security was not an issue. Consequently, they have to rely on the countermeasures implemented by the infrastructure networks they are connected to. A significant exception in this context, however, is represented by OPC UA Safety protocol that actually uses the native OPC UA security features. Finally, we would like to mention an interesting example of an industrial network that integrates security and safety, provided in [35]. In this paper, the authors describe an implementation of the CANopen protocol on real-time Ethernet networks that includes safety and security mechanisms.