The rise of technologies such as 6G networks, edge computing, and the Industrial Internet has led to a dramatic increase in the amount of data that needs to be transmitted over heterogeneous integrated networks. The resources of embedded devices limit the ability of the Industrial Internet to transmit data. While the multipath transmission mechanism can mitigate data transmission issues of low reliability and low real-time performance from the network-level perspective. As the complexity of industry applications increases, however, the phenomenon that the high-quality data transmission is subject to the influence of the underlying layer is becoming increasingly apparent. The paper aims to explores the possibility of multipath transmission protocol running on a real-time kernel from the perspective of the operating system, as there is a lack of research and reports in this area. Based on RT-Preempt, a real-time system RT-Linux suitable for the “NXP i.MX6Q” ARM integrated board has been proposed, which replaces the native Linux kernel to optimize and enhance its real-time performance. As described in the experiment part, the original standard Linux system OR-Linux and the new RT-Linux are tested with single-threaded and multi-threaded load experiments, respectively. The results of the analysis show that this paper provides a way of validating the trial data and ensuring its accuracy using the lognormal distribution model, which is a statistical distribution used to model variables that are positive and skewed to the right. The RT-Linux scheme has better real-time performance and is more stable than the OR-Linux scheme after real-time processing, showing the viability of the scheme.

Under the vision of industry 4.0, industrial networks are expected to accommodate a large amount of aggregated traffic of both operation and information technologies to enable the integration of innovative services and new applications. In this respect, guaranteeing the uninterrupted operation of the installed systems is an indisputable condition for network management. Network measurement and performance monitoring of the underlying communication states can provide invaluable insight for safeguarding the system performance by estimating required and available resources for flexible integration without risking network interruption or degrading network performance. In this work, we propose a data-driven in-band telemetry method to monitor the aggregated traffic of the network at the switch level. The method learns and models the communication states by local network-level measurement of communication intensity. The approximated model parameters provide information for network management for prognostic purposes and congestion avoidance resource planning when integrating new applications. Applying the method also addresses the consequence of telemetry data overhead on QoS since the transmission of telemetry packets can be done based on the current state of the network. The monitoring at the switch level is a step towards the Network-AI for future industrial networks.

Industrial real-time software is commonly evaluated on real embedded systems, while simulators are less used, since the abstraction level and purpose vary with for example, different programming languages and run-time contexts. This paper extends, applies, and evaluates previous work on a flexible task design that improve code reuse between discrete event simulators and embedded real-time systems. The paper focuses on two parts: (i) The performance cost of the proposed design in practice, by comparing the flexible task design with a traditional threaded approach. (ii) The potential of an alternative way to support legacy code in combination with discrete event simulation. The experiments indicate an almost negligible performance cost with respect to the real-time behavior, i.e., latency and jitter, while enabling improved code reuse between discrete event simulation and industrial embedded real-time systems.

Most evaluations of industrial real-time software are conducted on real embedded systems. The use of simulators that provides easily reproducible evaluations is often limited, due to different levels of abstraction, e.g., programming languages and run-time contexts. This paper extends previous work on a flexible task design, enabling tasks to be agnostic to run-time context, with evaluations conducted on bare-metal and real-time operating systems. Based on the same design and experiments we extend the proof-of-concept implementation in a discrete event simulation context, executing on a Windows based simulation host. Our experiments show that the flexible task design can be driven in a simulation run-time context, and still support typical industrial constructs. The result indicates that improved code reuse between discrete event simulators and industrial embedded systems is feasible.

Industrial control systems have strict requirements for time-sensitive applications and clock synchronization services. Performance of such applications is adversely impacted by packet delays and jitters. The impact is especially critical in process industries due to harsh environmental conditions. In this paper, we analyze delays and jitters to assess the performance of time-sensitive applications. To this end, we captured and analyzed round trip delay data retrieved from a paper factory. Analysis shows that a sub-millisecond level average delays and the jitters derived from the observed data are sufficient to meet the minimum 10ms update frequency required for most critical control applications. Moreover, the filtered delay variations at the end devices are less than the recommended 150us, which guarantees an adequate time synchronization accuracy in the factory network. Besides, this analysis can provide significant insights into performance bottlenecks for factory applications.

The run-time context in industrial embedded systems varies from bare-metal microcontrollers, to multicore-processors running real-time operating systems. Due to the longevity of industrial systems, reusability and evolvability are often considered crucial quality attributes. This paper presents a new flexible task design that enables tasks to be agnostic to run-time context. Evaluations of the design were made by conducting experiments using a proof of concept implementation of the proposed design. The experiments were based on typical industrial constructs, such as periodic tasks, and event signaling from interrupts. Findings from the experiments show that tasks can be more agnostic to run-time context and still deliver functionality normally used within industry. The results indicate that it is feasible to improve reusability and evolvability between different run-time contexts, and in addition, support hybrid configurations that can reduce resource usage, since e.g. a thread can be easily shared among several tasks.

This Special Section on "Security, privacy, and trust for Industrial Internet of Things" of the IEEE Transactions on Industrial Informatics (TII) highlights the main research challenges in the industrial Internet of Things (IoT) security, privacy, and trust. The designated nine high-quality research articles cover a wide range of the special section theme, including innovative solutions and novel technologies. These articles are briefly summarized.

In this paper, we consider a wireless energy harvesting network consisting of one hybrid access point (HAP) having multiple antennas, and multiple sensor nodes each equipped with a single antenna. In contrast to conventional uplink wireless networks, the sensor nodes in the considered network have no embedded energy supply. They need to recharge the energy from the wireless signals broadcasted by the HAP in order to communicate. Based on the point-to-point and multipoints-to-point model, we propose two medium access control protocols, namely harvesting at the header of timeslot (HHT) and harvesting at the dedicated timeslot (HDT), in which the sensor nodes harvest energy from the HAP in the downlink, and then transform its stored packet into bit streams to send to the HAP in the uplink. Considering a deadline for each packet, the cumulative distribution functions of packet transmission time of the proposed protocols are derived for the selection combining and maximal ratio combining (MRC) techniques at the HAP. Subsequently, analytical expressions for the packet timeout probability and system reliability are obtained to analyze the performance of proposed protocols. Analytical results are validated by numerical simulations. The impacts of the system parameters, such as energy harvesting efficiency coefficient, sensor positions, transmit signal-to-noise ratio, and the length of energy harvesting time on the packet timeout probability and the system reliability are extensively investigated. Our results show that the performance of the HDT protocol outperforms the one using the HHT protocol, and the HDT protocol with the MRC technique has the best performance and it can be a potential solution to enhance the reliability for wireless sensor networks.

Providing network reliability as well as low and predictable latency is important especially for Industrial Automation and Control Networks. However, diagnosing link status from the control plane has high latency and overhead. In addition, the communication with the industrial controller may impose additional network latency. We present FastReact - a system enabling In-Network monitoring, control and caching for Industrial Automation and Control Networks. FastReact outsources simple monitoring and control actions to evolving programmable data planes using the P4 language. As instructed by the Industrial Controller through a Northbound API, the SDN controller composes control actions using Boolean Logic which are then installed in the data plane. The data plane parses and caches sensor values and performs simple calculations on them which are connected to fast control actions that are executed locally. For resiliency, FastReact monitors liveness and response of sensors/actuators and performs a fast local link repair in the data plane if a link failure is detected. Our testbed measurement show that FastReact can reduce the sensor/actuator delay while being resilient against several failure events.

Trends like the Cloud, Internet of Things and 5G are pushing for an increase in connectivity, but, introducing a new type of network in an industrial distributed control system is a big investment with high risks. Time to market with sufficient quality is crucial. However, when getting through the Research and Development (R&D) phases, a lot of time is spent on isolated activates, e.g., simulations, collecting requirements, design, coding, debugging, creating testbeds, and performing various tests. Therefore, there is a need to improve efficiency when moving between the R&D phases. For verification and validation of communication software, the most common network evaluation method in industry are real testbeds, mostly since a testbed can be very similar to the deployed system. Testbeds are, however, hard to debug and costly to maintain. Other network evaluation methods like simulators, have some strengths that testbeds are lacking, like repeatability, control over the network, and lower cost. However, code from simulators can seldom be reused, especially in industrial time-sensitive target systems, due to different abstraction levels, run-time behavior and system timing. This paper presents findings from a case study that targets improved efficiency, getting from research theories, to deployed devices in a homogeneous Industrial Wireless Sensor and Actuator Network (IWSAN). We propose a small subset of network simulators features which eases changeability, reuse, and debugging of communication software. The selected simulator features are evaluated with a proof of concept implementation that is customized to a research platform. The findings indicate improved efficiency when moving back and forth between activities in different R&D phases.

The papers in this special section focus on wireless communication for use in automation of control and cyber-physical systems. Wireless communication is becoming increasingly important for industrial automation and many solutions have started to appear on the market. However, most of the available solutions target monitoring applications with slow refresh rates and with the downlink designed for best-effort traffic, thus neglecting actuators. Critical communication applications are defined as applications that require high reliability, i.e., that data packets are delivered with very high probability within a certain deadline, to avoid serious consequences (bodily injury, human losses, severe environmental impact, or great financial loss). It is challenging to simultaneously provide low latencies (end-to-end delay) and high reliability, especially over wireless links, which are inherently unpredictable. Suitable solutions exist that work well in specific contexts.

Industrial wireless sensor and actuator networks (IWSANs) offer significant advantages to industrial automation. However, high-reliability demands and hard communication deadlines pose challenges to its practical applications. To achieve this goal, flooding is considered as a promising approach due to multipath diversity and simplicity. In this paper, an enhanced version of REALFLOW, a flooding-based routing protocol for IWSANs is presented. Compared to the original REALFLOW, network management and network stability are improved. REALFLOW is compared with four other flooding protocols via simulations. The simulation results show that REALFLOW has better performance in terms of reliability and consecutive transmission errors when considering deadlines. Compared with normal flooding, REALFLOW achieves comparable reliability performance with decreased redundancy. Measurements from a prototype implementation conducted in an industrial manufacturing workshop reveal that high-reliability and low-application failure rates can be achieved, giving more confidence in providing reliable wireless sensing and actuating for industrial automation.

A growing concern of cyber threats towards industrial plants has prompted industrial practitioners to focus on secure communication solutions which can protect their systems from vulnerabilities and as well as their brand image. The security concerns and the solutions for industrial communication networks have become well-discussed topics in research communities. Despite a huge research effort in the area of industrial communication network security, there are several issues that need to be addressed properly such that a unified security solution can be adopted in the industrial domain. In this article, we aim to outline the research direction for industrial communication security. Though security is considered as an on-going process, the major issues that still need to be addressed are trust management for heterogeneous networks, managing network performance with security requirements, usable security and key management.

A trend in the industrial domain is that the networks are growing and becoming more complex, this is further accelerated by the digitalization trend. In order to address this, there is a need to improve the efficiency when moving between the R&D phases. For example, integrate innovative research findings into industrial systems, shorten time to market, improve product quality and reduce the number of issues. Despite a huge research effort on network simulators and emulators there are still some issues that needs to be addressed. This paper presents challenges that needs to be resolved, in order for the industry to adopt and benefit from using network simulators and emulators. The major challenges streamlining the workflow in and between the different R&D phases while preserving the real-time aspects in the entire industrial distributed control system.

Industrial wireless sensor and actuator networks are gaining momentum and have started to target new and more demanding application scenarios extending pure monitoring scenarios. In this paper we discuss the needs for simple and more accurate TDMA timing synchronization to enable the future applications. We present a novel TDMA timing synchronization protocol which is simple to implement, as well as a performance evaluation using of-the-shelf hardware indicating measured worst case synchronization errors less than 10 microseconds at five hops from the synchronization master. The paper shows that it is possible to realize synchronization on average around 1 microsecond with little effort and negligible computational or network overhead.

A key aspect of realizing the future smart grid communication solution is a balanced approach between the network performance and the network security during the network deployment. A high security communication flow path is not useful when the network path cannot support capacity and reachability requirements. The deployment phase in communication network can facilitate an optimal network path by focusing on both the network performance and the network security at the same time. In this paper, we describe a use case of smart grid application where security, network capacity and reachability needs to be optimal for successful network operation. We explain our proposed balancing approach of the network performance and the network security which can be useful for the optimal smart grid secure system design.

The papers in this special section focus on industrial wireless networks. With the rapid advance of wireless technologies, numerous emerging solutions and applications of industrial wireless systems have been developed. The present development of communication in industrial environments drives the need for ubiquitous access to distributed resources and services that are connected to things, devices, and systems. Service completions are typically perfected through smart APPS on wireless data delivery, such as WiFi, Bluetooth, ZigBee, and 5G. The occurrence of Internet of Things (IoT) further catalyzes the advent of the wireless era. These papers cover the comprehensive solutions of wireless network developments, industrial applications, and wireless prototype designs.

The security in industrial automation domain using cryptography mechanisms is being discussed in both industry and academia. An efficient key management system is required to support cryptography for both symmetric key and public/private key encryption. The key management should ensure that the device is verified before distributing the initial key parameters to devices. The software/firmware used in the device comes from manufacturers, therefore the initial authenticity of the device can be easily verified with the help of manufacturers. Mobile telecommunication is an industrial segment where wireless devices are being used for a long time and the security of the wireless device management has been considered through a standard driven approach. Therefore, it is interesting to analyse the security authentication mechanisms used in mobile communication, specified in Long-Term-Evolution (LTE) standard. This paper analyses the initial device authentication using public key infrastructure in LTE standard, and discusses if, where and how the studied solutions can be tailored for device authenticity verification in industrial plant automation systems.

In industrial plants, there is a mix of devices with different security features and capabilities. If there is a mix of devices with various degree of security levels, then this will create independent islands in a network with similar levels of security features. However, the industrial plant is interconnected for the purpose of reducing cost of monitoring with a centralized control center. Therefore, the different islands also need to communicate with each other to improve the asset management efficiency in a plant. In this work we aim to focus on the trustworthiness assessment of devices in industrial plant networks in term of node value. We study the behavior of industrial plant networks when devices with various degrees of security features communicate. We aim to identify network properties which influence the overall network behavior. From the study, we have found that the communication path, the order of different communication paths and the number of specific types of nodes affect the final trustworthiness of devices in the network.

Industrial networks have a mix of devices with different security properties. If a mix of devices with various degrees of security features and capabilities communicate, the overall network dynamics with respect to device trust and security of message exchange will be complex. Therefore, there is a need to understand the trust and risk probabilities of devices in a heterogeneous network. This is required for heterogeneous network where the network configuration has to be made based on how trustworthy they are. In this work we focus on assessing security risks for devices and message exchanges. We define the term assurance value to denote the resilience of a device to security attacks. We study the behavior of a communication network when devices with various degrees of security features exchange messages. We aim to identify the network security properties based on the network architecture. From the study, we propose a model to estimate and predict network security properties in a heterogeneous communication network.

TTEthernet is a communication platform which builds on Ethernet, but extends it to include fault-tolerance and real-time mechanisms. The existing TTEthernet technology is developed for wired networks. A natural step for improving and extending the current application field is the introduction of a mixed wired and wireless network. However, this step requires research both about possible adaptation of existing systems as well as implementation of new technologies. A central research question is the security aspects of real-time sensor networks using wired and wireless technologies based on TTEthernet. In this paper, we identify and classify the most important aspects to consider in order to provide secure communications in such safety-critical industrial applications and propose a potential solution to address identified issues.

In various industrial automation applications, positioning enables location awareness which can be exploited in applications such as robotic precision control, amongst others. This paper discusses positioning for industrial automation applications. Examples of applications from an infrastructure perspective are presented, and the integration of high precision positioning technology into existing network infrastructure for such applications is discussed, as well as challenges involved. An impulse-radio ultra-wideband 802.15.4a based system for high accuracy/precision positioning is presented, which shows promising results, therefore motivating the use of UWB as a high accuracy and precision technology for positioning applications in future industrial automation systems.

Industrial device commissioning along with the initial distribution of keying material is an important step for the security of industrial plants. An efficient key management system is required in cryptography for both symmetric key or public/private key encryption. Most of the key management system use either pre-installed shared keys or install keys using out-of-band channels. In addition to that, the sensor devices both wired and wireless need to be verified whether it is connected to the correct physical entity since these devices are linked with the physical world. Therefore in industrial plants there is a requirement to automate the trust bootstrapping process, where the devices from upper level in communication network will be aware that the communication device from below level is trusted. In this work, we present a workflow that uses the existing trust mechanism on employees to enable the initial bootstrap of trust in the devices, and also optionally support the commissioning engineer to download the required configuration data in the device as well. Thus, this approach presents a unique solution to the initial trust distribution problem reusing the existing features and facilities in industrial plants.

Applying Industrial Wireless Sensor and Actuator Networks (IWSANs) in the industrial automation is a growing trend due to flexibility, mobility and low cost. According to the current standards, such asWirelessHART and ISA100.11a, multi-channel TDMA transmission is included for reliable and deterministic communication. In this paper, we clarify the dependence of TDMA scheduling for sensors and actuators and point out the low correlation between the scheduling delay and the overall quality of control, and focus on reducing jitter in scheduling for improving quality of control and system stability. We propose a scheduling algorithm, aiming for lowing jitter and compare it with two traditional real-time scheduling schemes. Our simulation results exhibit significantly lower jitters by applying our scheduling policy than those two traditional scheduling schemes.

The security of industrial plants has gained a lot of importance since the last decade. The reason is that the different components from different network layers of automation systems have become inter-connected to support fast and cost-effective decisions at the management level. This inter-connectivity has posed many security challenges in this industrial segment. To achieve effective security mechanisms in industrial plants, there is a need to learn from other existing domains, matured in terms of security, whether existing matured security solutions can be reused in the industrial automation domain. The financial sector is a segment where security has been carefully managed since a long time, as security is very important for that sector. Therefore it would be beneficial to evaluate the security mechanisms present in financial card readers which are involved in financial transactions because these card readers have many similar characteristics with industrial process control devices. In this paper, the security requirements for both the field devices of industrial plants and card reader terminals of the financial sector have been evaluated to understand the security gap so that we can identify the areas where the security needs of industrial plants must be improved and where some of the existing security features of card reader terminals can be reused in field devices of industrial plants.

Several wireless sensor network (WSN) applications will in the future be deployed for process control purposes which typically require timely data delivery. The main drawback with current WSNs is that they cannot guarantee predictable delay which is required in many applications. In this paper, we propose WirArb which is a new medium access control (MAC) protocol suitable for time-critical applications that needs deterministic delay guarantees. Each user is pre-defined arbitration frequency which is used to distinguish in which order the users can access the channel. The arbitration frequency is determined by orthogonal sub-carriers in the physical layer. The proposed mechanism will always guarantee the user with highest priority will gain channel access and users with lower priority needs to wait for their turn. We evaluate and compare the proposed WirArb with IEEE 802.15.4 and IEEE 802.11 in terms of latency and throughput. The obtained results show that for a star network with several users the proposed WirArb is superior.

In this work we propose an Adaptive Forward Error Correction (AFEC) algorithm for best effort Wireless Sensor Networks. The switching model is described in terms of a finite-state Markov model and it is based on the channel behavior, observed via Packet Delivery Ratio in the recent past. We compare the performance of AFEC with static FEC, as well as uncoded transmissions. The results demonstrate a gain in PDR achieved by introducing FEC coding in uncoded IEEE 802.15.4 transmissions, as well as the advantages over static FEC schemes, namely increased throughput and reduced energy consumption. The proposed solution is IEEE 802.15.4-compliant and requires no additional feedback channels.

High reliability and real-time performance are main research challenges in Industrial Wireless Sensor Networks (IWSNs). Existing routing protocols applied in IWSNs are either overcomplicated or fail to fulfill the stringent requirements. In this paper, we propose a reliable and flexible Received Signal Strength-based routing scheme. Our proposed solution can achieve a seamless transition in the event of topology change and can be applied in different industrial environments. The simulation results show that our solution outperforms conventional routing protocols in both reliability and latency. Furthermore, the result also proves that the changes of the network topology have no impact on data transmissions of other nodes by our scheme, whereas conventional routing protocols are shown to fail to recover the network in a short time. Finally, due to dynamic weighting mechanism, the proposed scheme is verified to achieve significantly higher reliability in scenarios with obstacles and avoid installation troubles, compared to location-based flooding scheme. Thus, our proposed scheme is considered to be more suitable for IWSNs than other routing protocols.

In this paper we address the issues of timeliness and transmission reliability of existing industrial communication standards. We combine a Forward Error Correction coding scheme on the Medium Access Control layer with a lightweight routing protocol to form an IEEE 802.15.4-conformable solution, which can be implemented into already existing hardware without violating the standard. After laying the theoretical foundations, we conduct a performance evaluation of the proposed solution. The results show a substantial gain in reliability and reduced latency, compared to the uncoded transmissions, as well as common Wireless Sensor Network routing protocols.

Contrary to the various theoretic publications on safety-critical communication over wireless, this paper will show the actual performance of safety-critical communication in a real plant with all its environmental influences. We used PROFIsafe as a functional safety profile on top of the WirelessHART protocol. Separately these technologies are widely used in industry for safety and wireless communication respectively, but it has never been shown that the combination of them is feasible for safety-critical communication. The main focus of this work is to measure and analyze the round-trip time and the bit error rate of the safety-critical communication in order to identify whether the certification requirements of PROFIsafe holds. We will show that it is technically feasible to run safety-critical data over wireless links. However, long round trip times and high noise in the channel at certain locations in the plant are unacceptable with respect to certification and need further investigations.

Two major trends can be recognized in industrial automation. One of them is that Ethernet is replacing traditional fieldbus networks continuously, because it combines flexibility, reliability, and introduces fast data rates, which allow beside others quality of services. This is pushed even further when field devices use wireless communication to connect to the control system. Beside that another trend is seen in functional safety due to rising customer demands and evolving regulations in industry. That leads necessarily to a consolidation of both technologies, where safety must be guaranteed in the same manner over wireless channels as it is handled over Ethernet. This paper addresses safety issues emerging when PROFIsafe, as one of various safety protocols on the market, is used on top of a black channel layer, that is comprized of non-safe protocols including WirelessHART.

We analyze here the topic of integration, in the area of process automation, from sensor/actuator levels to plant management levels. The communication at fieldbus level is based on wireless technology while management applications run in wired control systems, but can also be distributed, communicating via the Internet. This work aims at building a real-life demonstrator at Boliden, a mining and smelting plant located in Boliden, Sweden. A small process control environment is to be deployed at the plant to supervise a tank level control system. Targeted results are an interface between wireless and wired systems, the deployment of a wireless process control environment at Boliden, and the development of the enterprise business management facilities.

In this paper we show that it is possible to retrofit a security layer on top of PROFINET IO without changing the underlying transmission system or standards. By introducing security modules, end-to-end network security can be achieved and ensure authentication, integrity and confidentiality for real-time communication. The concept of security modules is a flexible framework and countermeasures can be changed, as security threats and exploits are changing over time. A proof-of-concept implementation shows that it is possible to implement security modules on existing products and secure them against, for example, man-in-the-middle attacks.