Resilient systems are crucial for modern interconnected applications, especially those with autonomous machine-to-machine communication. Standard network protocols can exhibit unacceptable recovery times for time-critical operations, and systems must withstand various disruptions beyond just connection failures.This paper addresses these vulnerabilities by proposing a robust communication architecture based on an adapted MQTT protocol employing duplicated packet transmission over parallel pathways. The approach, based on redundancy, employs a smart algorithm for selecting the best communication path to rely on. This strategy aims to ensure reliable data delivery and mitigate service interruptions, particularly for demanding industrial applications, while limiting resources and bandwidth consumption. The effectiveness of this architecture is validated through a real testbed implementation and online testing.

The extension of Time Sensitive Networking (TSN) to wireless domains is a key enabler for the realization of Industry 4.0 and 5.0 applications. Thanks to their characteristics in terms of latency and bandwidth, and the seamless integration with Ethernet TSN, 5G New Radio (NR) and 802.11 (WiFi) are the primary candidates for enabling wireless TSN applications. In the TSN context, precise time synchronization represents a funda-mental building block. In this paper, we focus on the assessment of the synchronization accuracy of IEEE 1588 (PTP) over 5G NR networks by considering different network configurations and traffic loads. The results provide preliminary insights into the performance of PTP over 5G NR and its suitability for TSN applications.

Critical infrastructure, utilities, and large enter-prises are increasingly complex. These sprawling systems, often geographically dispersed, rely on seamless coordination across vast networks. Typically, they use the internet and TCPIIP proto-cols for communication. However, ensuring system-level resilience requires exceptionally dependable network infrastructure. This paper proposes a solution built on a redundant version of the MQTT protocol, implemented directly at the network's endpoints. This approach ensures reliable communication even in the face of potential network issues. Additionally, the paper explores the potential for a future solution that analyzes multi-publisher/subscriber scenarios and, for this purpose, a prelimi-nary research on synchronizing communication among a larger number of devices within the network. The paper concludes by detailing the proposed solution, evaluating its effectiveness, and validating its practicality through experimentation.

The ever more used and widespread Time-Sensitive Networking (TSN) has changed real-time networks, enabling reliable communication for time-critical applications. At the same time Software-Defined Networking (SDN) has emerged as a solution to ensure proper quality of service for managing dynamic network configurations even in evolving topologies. This paper investigates the integration between TSN and SDN to enable dynamic network re-configuration and improve performance for time-critical applications. We present an experimental setup designed to evaluate this approach. The setup focuses on scenarios where an SDN controller can dynamically reroute critical data flows across different TSN network devices to avoid interference and maintain consistent Quality-of-Service (QoS).

Nowadays, large enterprises, critical infrastructures, and utilities are complex systems, and consist of a number of sub-systems, often located far away from each other, that coordinate their operations over geographic networks. Typically, they are interconnected through the Internet and communicate by means of TCP/IP-based protocols. When system-level resilience is required, extremely high dependability is demanded from the network. In this paper a solution is described and evaluated that loosely resembles SDN architectures. A redundant version of MQTT is used for the data plane, whereas an adaptive mechanism is implemented in the control plane that evaluates the quality of paths and dynamically selects the best choice. To maximize dependability, yet keeping resource consumption to acceptable levels, concepts borrowed from Reinforcement Learning are exploited. An experimental campaign corroborated our expectations and showed the practical feasibility of our proposal.

The introduction of Time-Sensitive Networking (TSN) is revolutionizing real-time networks and time-critical applications. Recent advancements in this field extended the TSN capabilities to wireless technologies, giving rise to the concept of wireless TSN (WTSN). This paper focuses on the integration of wireless TSN with Software-Defined Networking (SDN) to enable dynamic network configuration and improve the performance of time-sensitive applications. We present a practical test environment that uses a hybrid network configuration consisting of wireless and wired TSN links. The primary objective is to evaluate the effectiveness of combining a TSN-capable network with an SDN controller. This setup enables dynamic configuration and routing within the system, allowing for prompt actions to address network issues, such as seamlessly re-routing data paths between the two links due to an increase in latency or packet loss. A measurement setup using OpenVSwitch in the wireless TSN domain is presented, along with the evaluation of time synchronization and dynamic route selection capabilities.

Communication quality of wireless links unavoidably varies over time, for a number of reasons that are mostly unknown in the design phase of distributed systems. This is a severe limitation when such network technologies are employed to connect devices and subsystems in industrial applications, where high reliability and timeliness are customarily demanded. The ability to foresee, to some extent, the quality of a link in the near future is likely to provide clear benefits in many such cases.In this paper, we analyzed and compared the performance of two approaches, based on simple moving averages and artificial neural networks, respectively, to carry out predictions for a real Wi-Fi link. Results confirm that reliable estimates about the packet delivery ratio can be obtained in realistic operating conditions by averaging the recent past, and that the use of machine learning may improve prediction further.

Controller Area Network is still the most popular solution for in-vehicle communications in automotive scenarios. Recent solutions like CAN FD and CAN XL manage to reduce the performance gap with Ethernet-based solutions. Nevertheless, the priority-based access mechanism they rely on is not completely adequate to support fragmented transfers of large blocks of data, as happens, e.g., for driver assistance and the Internet of Things. In this paper, a slight modification is proposed for the basic CAN access mechanism that permits a group of objects to be served by the network with about the same quality of service. This provides fair treatment to a number of block transfers initiated by different nodes and taking place contextually over the bus.

Among the application layer protocols that support the Internet of Things, a very popular option is MQTT. Its main advantages reside in the inherent simplicity, which makes it suitable for embedded devices too, and the publisher-subscriber model it relies on, which decouples data sources and sinks and enables efficient multicast streaming over the Internet. In this paper a proposal is described that exploits redundant MQTT brokers, deployed in different geographic locations, whose aim is to provide uninterrupted service in spite of failures that may be affecting both the servers executing the middleware and the Internet core. Unlike routing algorithms and protocols, seamless redundancy features zero intervention time, making this solution suitable for critical infrastructures where timings are relevant, like public utilities and some large enterprises.

The past few decades saw factory and process automation move from monolithic to fully distributed architectures, where the communication system plays a key role in providing higher flexibility and availability, yet fitting the peculiar requirements of such contexts. As part of the Industry 4.0 (r)evolution, the Industrial Internet of Things is meant to achieve full convergence toward well-agreed non-proprietary digital networking technologies. In this scenario, OPC UA is becoming increasingly relevant as a high-level protocol to exchange information in heterogeneous distributed industrial applications. In this paper, the performance of OPC UA has been evaluated by means of an experimental measurement campaign carried out on real devices connected to real networks. In particular, we analyzed how much the end-to-end notification latency achieved by the subscription mechanism is affected by the position and interconnection of devices, their specific implementation, and configuration parameters. Outcomes can be helpful in designing systems where industrial devices interact with local workstations, the edge, and the cloud, to understand whether or not timing constraints of applications will be met.

Among the many enabling technologies Industry 4.0 relies on, the Industrial Internet of Things is a relevant one that enables both horizontal and vertical integration in modern enterprises, to accomplish complex functions that exploit either cloud or edge processing. In particular, the OPC UA protocol is knowing an ever increasing attention for interconnecting devices, equipment, and facilities in next-generation plants. This work focuses on the characterization of the notification latency in distributed systems that rely on the OPC UA publish-subscribe paradigm for interactions. In particular, starting from a black-box experimental evaluation carried out on real setups, we tried to explain the seemingly peculiar behavior of some popular solutions by means of theoretical models complemented with code inspection.

TSCH is emerging as a reliable access mechanism for wireless sensor networks that, thanks to time slotting, suits the needs of battery-powered devices deployed in industrial scenarios. To take into account the traffic needs of the different links in a mesh network and the related variability, in such a way to prevent instability and butter overruns, overprovisioning can be exploited. It consists in allocating more cells than strictly needed for communication between a node and its neighbors. Unfortunately, overprovisioning in TSCH leads to higher power consumption, because of idle listening. In this paper, two approaches for saving energy are proposed, which temporarily disable listening when no packets are available at the transmitter. Such mechanisms show good backward compatibility with existing TSCH devices, and may coexist with them.

Industrial Internet of Things demands high reliability and determinism on the one side, and easy interconnection with the existing network infrastructures on the other. A very promising class of solutions combines IEEE 802.15.4 Time Slotted Channel Hopping, to meet above communication requirements, and IPv6, to provide universal connectivity. Products compliant to this approach have recently begun to appear off-the-shelf.In this paper, two such solutions have been taken into account, namely SmartMesh IP and 6TiSCH. Their performance has been experimentally evaluated by taking into account metrics relevant to industrial applications. Since we aimed at providing a practical feedback to designers of industrial systems, devices were tested using their default configuration. Results provide valuable experimental figures on what engineers can expect from these technologies, which includes seamless connectivity and a reasonably high resilience to interfering traffic.

The Industrial Internet of Things is currently gaining momentum in production plants as a way to efficiently support a number of functions, e.g., preventive maintenance. To this extent, a number of solutions have been proposed in the past few years, which typically rely on a layered approach. In this paper, a general-purpose architecture is presented for factory automation systems, which mimics the industrial networks used at the shop-floor. In particular, it relies on a modular structure for devices and protocols aimed at reducing implementation effort, so as to ease its adoption in real-world applications. A preliminary experimental testbed based on such architecture has been set up, and it operations verified.

Industrial communication systems represent one of the most important innovations of the last decades in the context of factory and process automation systems. They are networks specifically designed to cope with the tight requirements of these challenging application fields such as real time, determinism, and reliability. Moreover, industrial networks are often deployed in environments characterized by strong electromagnetic interference, mechanical stress, critical temperature, and humidity. Over the last three decades, different classes of industrial networks have been developed according to changing requirements and available communication and information technologies. In this paper, we first provide an account of the state of the art, reviewing classical fieldbuses, real-time Ethernet networks, and industrial wireless networks, along with their most relevant features, applications, and performance figures. We introduce the complex standardization framework and analyze the market status and assumptions for future development. In the second part, we address the future perspectives focusing on new technologies, standards, and fields of application. In particular, we consider the time-sensitive networking (TSN) family of standards, Industrial Internet-of-Things (IIoT) systems, high-performance wireless LANs, industrial applications of cellular networks, and Ethernet networks for automotive communication.

The eleven papers in this special section focus on industrial communication systems and technologies (ICS). Major requirements of the ICS are real-time support and dependability under all considered load and fault assumptions. The ICS may need to meet stringent deadlines as a basis for the stability in control loops and alarm monitoring. At the same time, high reliability and availability is demanded to avoid down times. In particular, reliability with respect to critical failure modes is of utmost importance for safety-critical applications where failures may result in significant financial losses or risk to humans and the environment. From the point of view of the information and communication technology (ICT), current ICS solutions are based on wired systems to support distributed industrial controls.

Communication over the ether is by nature erratic, and thus wireless networks are often deemed unsuitable to support time-critical distributed control applications, like those at the shop-floor of industrial plants. However, scheduling techniques derived from real-time operating systems, along with channel redundancy and runtime retransmission management, can be profitably applied to wireless networks to improve their determinism tangibly. This paper presents a novel approach that combines such solutions. A preliminary prototype implementation, which relies on IEEE 802.11 (Wi-Fi), has been set up to assess feasibility and performance of the approach. Results show that determinism of data exchange can be improved to a degree that makes wireless networks actually suitable for many soft real-time applications.

Industrial distributed control systems would greatly benefit from the adoption of wireless communication technologies, if only guarantees could be provided on timing of time-critical data delivery over the ether. This paper presents solutions to handle single-hop deadline-constrained periodic traffic, which combine centralized transmission scheduling according to earliest deadline first (EDF) and automatic repeat request (ARQ). For each solution, an admission control test is provided, which guarantees a configurable number of retries to each data instance within its deadline, statically addressing both timeliness and reliability on a per-instance basis. Dynamic bandwidth management strategies are also introduced that use runtime information about unperformed guaranteed retries and reassign them, as extra retries, to failed instances whose deadline has not yet expired. Simulation results show that significant benefits can be obtained, in terms of both determinism and improved performance, by a careful static/dynamic management of the available communication resources.

The connection of control and process networks to company infrastructures and the Internet, besides offering undeniable advantages, also imposes the adoption of adequate security countermeasures. Specialized firewalls, able to recognize and inspect traffic concerning peculiar communication protocols such as Modbus, which are commonly adopted in industrial applications, are beginning to spread on the market. However, several industrial control systems (ICSs) must satisfy critical performance and timing requirements and the impact of introducing such a kind of devices in an existing network should be evaluated carefully. In this paper we present a simple approach based on ordinary equipment and open source software, which can help system designers and managers to get approximate but useful information about effects produced by including an industrial firewall in their system. The proposed technique, though quite simple, has the advantage of circumventing the need of ad-hoc measurement instrumentation and can be used also by non-experts, virtually with little or no effort, to get rough guess indications about the extent the firewall insertion in the network can be tolerated.

Communication over the ether is by nature erratic and, consequently, wireless networks are unsuitable for hard real-time distributed control applications typical of industrial plants. However, scheduling strategies employed by real-time operating systems, along with channel redundancy and advanced bandwidth management, can be used to improve their determinism and make them suitable for soft real-time applications. This paper presents an approach that combines such techniques and a preliminary implementation, which relies on IEEE 802.11 (Wi-Fi), employed to assess its feasibility. Results show that data exchange determinism can be substantially improved towards the level required by many soft real-time applications.

Timeliness and reliability are two major requirements of control systems and this true, in particular, in many industrial application areas which make use of solutions distributed over a network. Moreover, with the adoption of wireless communication technologies in industrial environments, granting timeliness and reliability for transmissions over the wireless error-prone channel has become a challenge of primary importance. This paper presents a new technique which is able to grant the feasibility of a set of real-time periodic data exchanges over a wireless network in presence of retransmissions. Thanks to a dynamic bandwidth reassignment strategy, our solution is also able to cope with retransmissions efficiently, so as to improve the system performance in terms of overall data delivery success probability and without negatively affecting the real-time guarantees.

This paper describes reference broadcast infrastructure synchronization (RBIS), a clock synchronization protocol for IEEE 802.11 infrastructure wireless networks. The protocol is especially tailored for industrial and home automation networks, and in many application contexts, it offers several advantages compared with other solutions targeted at similar purposes. RBIS has been conceived to rely on conventional Wi-Fi equipment and, in particular, on unmodified access points. It is based on the master/slave approach and follows the receiver/receiver paradigm. An implementation of RBIS-carried out completely in software and based on timestamps taken at the interrupt handler level-has been developed, which achieves a synchronization error below 3 μs. Then, a simple distributed hard real-time control application has been setup, which consists in two PCs running real-time application interface for Linux (RTAI) and connected through Wi-Fi. The actuation error, measured on the generation of synchronous pulses, is strictly below 13 μs.

Wireless communications suffer from disturbance and interference, which prevent reliable data exchanges and preclude their adoption in the real-time applications found at the lower levels of factory automation systems. This is particularly true for Wi-Fi, for which mechanisms like channel hopping and blacklisting are not available. Several solutions were defined in the past few years, which range from the adoption of general-purpose redundancy protocols over conventional communication equipment to proposals like Wi-Red, which offers link-level redundancy. In this paper, an enhancement is presented for the latter solution, which achieves better performance by deferring transmission of duplicate frames. The net effect is a sort of load balancing between wireless channels, which reduces network traffic and increases reliability further.

In this paper the RBIS synchronization protocol is presented, which has been specifically conceived for industrial infrastructure WLANs. It combines the concepts of the sender/receiver and receiver/receiver approaches: similarly to RBS, timestamps are recorded only on received frames while, like IEEE 1588, it permits slaves to synchronize to the same master clock. Compared to RBS, RBIS has several advantages. Every single wireless sub-network, in fact, can be easily synchronized with an external time source located on the wired backbone. Moreover, when software implementations are considered that rely on unmodified conventional WiFi equipment, RBIS is able to feature noticeably better timing accuracy than IEEE 1588.

EtherCAT is a real-time Ethernet protocol conceived explicitly for industrial applications. It is characterized by high communication efficiency, which permits control loops to be closed with short cycle times, and is provided with a suitable mechanism, known as distributed clock (DC), that enables synchronized operations to take place across the controlled system. These features can be profitably adopted, for instance, to support motion control applications. In this paper, the performance of the DC mechanism is evaluated by means of a thorough campaign of experimental measurements carried out on a real network setup. A number of factors have been taken into account that can affect accuracy and precision, and their effects studied in depth.

At present, two important trends in industrial environments are the adoption of Ethernet-based technologies to interconnect devices and the use of PCs provided with open-source real-time operating systems to execute control applications. This makes the implementation of distributed control systems easier and inexpensive. In these cases, it is of utmost importance that response times concerning the messages exchanged over the network be deterministically bounded. In this paper, the contribution to the end-to-end transmission delay which is due to the latencies introduced by the local protocol stack is analysed through experimental evaluation. In particular, two popular stacks have been taken into account, that is the one provided in conventional Linux and RTnet.

At present, an increasing number of distributed control systems are based on platforms made up of conventional PCs running open-source real-time operating systems. Often, the need arises in these systems to have networked devices supporting synchronized operations. In this paper, an inexpensive solution is introduced, described, implemented and evaluated that relies on standard software and protocols such as RTAI, RTnet and IEEE 1588. The main goals of this architecture are reducing design and development costs, ensuring adequate synchronization accuracy, and easing the porting of control applications to different H/W and S/W configurations.

EtherCAT is a popular, real-time Ethernet network that features very high communication efficiency. However, because of the ring topology it relies on, cycle times increase when the network size grows larger (considering both the amount of process data and the network extension). In this paper a solution based on commonly available off-the-shelf switches is presented and analyzed that can improve performance for large automation systems. Such an approach (almost) does not require new custom h/w to be purposely developed.

Nowadays, wireless communication technologies are being employed in an ever increasing number of different application areas, including industrial environments. Benefits deriving from such a choice are manifold and include, among the others, reduced deployment costs, enhanced flexibility and support for mobility. Unfortunately, because of a number of reasons that have been largely debated in the literature, wireless systems cannot be thought of as a means able to fully replace wired networks in production plants, in particular, when real-time behavior is a key issue. In this paper, an analysis of the real-time performance that can be achieved in quality-of-service (QoS)-enabled 802.11 networks has been carried out. In particular, a detailed analysis of latencies and packet loss ratios for a typical enhanced distributed channel access (EDCA) infrastructure wireless local area network (WLAN) is presented, obtained through numerical simulations. A number of aspects that may affect suitability for the use in control systems have been taken into account, including the Transmission Opportunity (TXOP) mechanism, the internal architecture of the AP, the use of a time-division multiple access (TDMA)-based communication scheme as well as the adoption of broadcast communications.

EtherCAT is a popular Ethernet-based solution conceived for connecting devices at the shop floor in industrial environments. Even though it features very high communication efficiency, that permits thousands of I/O points to be periodically exchanged between controlling devices and decentralized periphery with cycle times well below 1 ms, it is not able to cope in a proper way with event-driven systems, where lots of devices may be producing asynchronous information in a sporadic and unpredictable way. In this paper, some modifications to the basic EtherCAT protocol are proposed which enable CAN-like arbitrations to take place in such networks, so as to achieve a true priority-based access scheme.

Nowadays, industrial communication systems are experiencing the introduction of wireless technologies at all levels of automated factories. The benefits that derive from such a choice are manifold, including reduced deployment costs, enhanced flexibility and support for mobility. Unfortunately, because of a number of reasons, wireless systems can not be thought of as a complete replacement of wired networks at the field level. In this paper, the performance that can be achieved by QoS-enabled WLANs to support communication in industrial environments is analyzed. In particular, a detailed analysis of latencies in infrastructure networks is presented, obtained through numerical simulations, that takes into account both media access and queuing delays. Moreover, the impact of the internal architecture of the access point on performance is evaluated as well.

The employment of real time Ethernet networks in factory automation systems is rapidly increasing and several commercial products, with different characteristics, are already available from various manufacturers. Most of these networks have been included in both the IEC 61158 and IEC 61784 International standards that, in addition, define a set of Performance Indicators. In this paper we focus on two popular real time Ethernet networks, namely Ethernet POWERLINK and EtherCAT, and we evaluate their performance for a typically deployed factory automation configuration. Specifically, we compute the most relevant performance indicators introduced by IEC 61784 standard and two (purposely defined) additional ones, namely minimum cycle time and jitter, which are suitable for the two networks considered.

The industrial communication scenario is experiencing the introduction of wireless networks at all levels of factory automation systems. The benefits deriving from such an innovation are manifold, even if wireless systems cannot be thought as a complete replacement of wired networks. Rather, they will be even more used in the near future to realize hybrid (wired/wireless) configurations. In particular, it is envisaged that wireless networks may be employed to implement extensions of (possibly already installed) wired systems. In this paper we consider wireless extensions of Ethernet Powerlink, a very popular Real-Time Ethernet network, implemented by means of the IEEE 802.11 WLAN. Specifically, we focus on a widespread network configuration and address two types of extensions based on, respectively, bridge and gateway devices. In the second part of the paper we provide an analysis of the hybrid networks aimed at evaluating the most relevant performance indexes. Since the reliability of wireless networks may represent a critical aspect, the analysis is carried out taking into account the presence of interference as well as fading in the wireless segment. The results we show, obtained from a theoretical analysis and validated by numerical simulations, allow to get some useful insights on the overall performance of the hybrid networks.

EtherCAT is a very popular solution for connecting control applications to field devices in industrial environments, which is based on Ethernet transmission technology. Even though EtherCAT features a very high level of communication efficiency, that permits thousands of I/O points to be periodically exchanged between the controlling device and the decentralized periphery with cycle times well below lms, it is not able to cope in a proper way with event-driven systems, where lots of devices may be producing asynchronous information sporadically and unpredictably. In this paper, a modification to the basic EtherCAT access scheme is proposed, which enables a CAN-like arbitration to take place in such networks in order to select the most urgent event pending for transmission.

In the last years the use of Ethernet as the communication technology for automation systems has been sensibly increasing. In particular, real-time Ethernet networks have become widely adopted. In this paper we consider one of the most popular Real-Time Ethernet networks, namely EtherCAT. We firstly provide a short outline of the protocol, along with a description of a simulation model we have developed. Subsequently, we focus on some typical network configurations and provide some insights on their performance by means of both theoretical analysis and numerical simulations.

Large diffusion of wireless communications is a trend that will soon involve industrial environments, too, and in particular those applications where granting limited response times is of utmost importance. This paper analyzes the impact of a number of causes, besides the medium access technique, on the performance of real 802.11g networks. In particular, the extent to which beacon frames and traffic on nearby channels can decrease the communication performance is taken into account, as well as the effect of the adapter's and access point's overheads on frame transmission latencies.

With the large diffusion of wireless communication industrial environments will soon be involved, including those applications where granting limited response times is of utmost importance. Delays are important issues for soft real-time applications and this paper analyzes the impact of a burst traffic on the performance of real 802.11g and 802.11e networks. In particular, how some stations that generate burst traffic, for example alarm storms, can create problems on a communication on the same priority class (802.11g) or on an higher priority class (voice over 802.11e). An analysis on this topic and some measurements are presented.

Abstract Scientific research and practical applications of solar physics require data and computational services to be integrated seamlessly and efficiently. The European Grid for Solar Observations (EGSO) leverages Grid‐oriented concepts and technology to provide a high‐performance infrastructure for solar applications. In this paper, an architecture for a data brokerage service is proposed. Brokers interact with providers and consumers in order to build a profile of both parties. In particular, a broker interacts with providers in order to gather information on the data potentially available to consumers, and with the consumers in order to identify the set of providers that are most likely to satisfy specific data needs. The brokerage technique is based on a multi‐tier management of metadata. Copyright © 2006 John Wiley & Sons, Ltd.

The adoption of wireless communication technologies in industrial environments for supporting (soft) real-time applications heavily depends on the ability to grant bounded response times for messages, at least from a probabilistic point of view. This aspect is particularly important in factory automation systems, where response times are considered much more significant than other performance indices, such as throughput, that are usually considered in different application areas. The ever-increasing availability on the market of products and solutions based on the IEEE 802.11 standard and the introduction of the 802.11e amendment for enhancing the quality of service (QoS) and prioritizing traffic make this kind of communication technology interesting also for adoption in (loosely coupled) distributed control systems. This paper reports on some experimental measures and the related analysis that have been carried out on real 802.11g/e networks for better understanding the statistical distribution of response times and can be of help in characterizing these solutions when used to support noncritical real-time traffic.