Securing industrial networked infrastructures has become increasingly important since the growth in their connectivity brought by production digitalization and the diffusion of paradigms such as Industrial Internet of Things (IIoT). Network segmentation is considered best practice to protect these networks from outside/inside cyber-attacks. To this purpose, network devices equipped with forwarding/filtering capabilities need to be suitably configured and deployed for the enforcement of segment-related security policies. Configuration of these devices in today industrial networked infrastructures is typically the result of a mix of manual and automated processes and, given the heterogeneity of devices and configuration languages, as well as of the supported applications and related requirements, it is often hard to make sure of its correctness and impact, e.g., on traffic latency. In this paper, a model is proposed to jointly describe network forwarding and filtering configuration. Techniques are then provided to perform static analyses such as verification of reachability intents and configuration equivalence, as well as the estimation of the latency introduced for handling specific traffic.

Open-source software firewalls are becoming a viable solution to protect industrial networked systems and critical infrastructures. In fact, the adoption of technologies and devices originally conceived for general purpose computer networks and the consumer market has been proven to both reduce costs and enhance performance also in the industrial scenario. The goal of this paper is to start investigating the behavior of Linux IPFire in the light of its possible adoption in industrial applications and to provide a baseline for the development of techniques designed to improve the filtering capabilities in multi-firewall networks.

Firewalls are popular cyber-security countermea-sures that are increasingly used in industrial environments to protect the network infrastructure from attacks and malicious behavior. Unfortunately, they can also become inadvertent bot-tlenecks when the traffic load they have to filter grows larger. Among the different solutions that have been proposed to mitigate this aspect and improve performance of devices, rule migration looks appealing also in industrial multi-firewall systems because, differently from other techniques appeared in the literature, it neither requires interventions on the network topology nor it is based on non-standard packet formats and protocols. This paper is aimed at presenting some preliminary results about performance achievable with the rule migration approach, when it is applied to the popular Iptables open source firewall, in the light of its possible adoption in industrial application scenarios.

Saving motes energy as much as possible is a main requirement in wireless sensor networks. Time Slotted Channel Hopping (TSCH) is an effective solution, as the radio module of receivers is enabled only when a frame reception is scheduled. Unfortunately, this often leads to non-negligible idle listening, i.e., the receiving interface is switched on but no incoming frame is detected. In cases where the traffic pattern can be somehow predicted, Proactive Reduction of Idle Listening (PRIL) techniques can reduce energy wastes significantly by temporarily switching receivers off. In this paper two specific strategies are proposed, which are aimed at improving PRIL robustness in the case acknowledgment frames are lost, hence causing the transmitter and receiver to have different perceptions of the link state. They were encoded by means of a discrete event simulator and their behavior analyzed. Results obtained through an extensive experimental campaign show that there is no clear winner. Instead, each proposed strategy is suitable for specific application contexts.

The dynamic redistribution of filtering rules between firewalls, which are located in the same network, is a technical solution that can cope with temporary changes in the traffic load processed by the firewalls themselves. This paper presents a novel formal model for networks including multiple cascaded firewalls, that can be leveraged to enable the transfer of a set of rules from a firewall to its downstream neighbors when the changes in the input traffic profile suggest to do so. With respect to other solutions appeared in the literature a formal approach, besides providing unambiguous specifications and mathematical proofs of correctness, also enables the computation of theoretical bounds for the expected performance before the proposed scheme is actually deployed in the target network. The underlying mechanism, on which our approach is based, is the reduction of the average number of rules checked per packet in order to increase the packet processing rate. Our network model takes into account both the system topology and firewall characteristics. A suitable transformation algorithm is then introduced, which is able to preserve the security integrity of the network while moving rules between cascaded firewalls and allowing tangible performance improvements in terms of packets processing rate for a given traffic profile. Correctness of the proposed solution has been formally proven and validated by means of simulation. Performance figures have also been obtained by running the proposed algorithm in a laboratory experimental test-bed.

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.

The availability of performance studies and simple models for firewalls able to deal with industrial application-layer communication protocols, such as Modbus/TCP, is crucial when the impact of these devices has to be estimated, even roughly, before their actual deployment in industrial networks. Unfortunately, most manufacturers do not provide this kind of information for commercial off-the-shelf available products. Thus, a viable solution is the development and experimental validation of simple models that can be used by designers to predict those firewall characteristics not explicitly related to their security capabilities. As an example, latency introduced on message forwarding is an aspect of significant interest in many industrial control systems, where delays and jitters in data delivery can severely impact on the effectiveness of the control actions. This paper reports on our experience in developing a performance model for a commercial device able to perform advanced application-layer filtering, in particular of Modbus/TCP traffic. A set of ad hoc designed experiments, performed by means of a purposely developed laboratory testbed, enabled both model development and validation, confirming a good correspondence of the estimated performance with the device actual behavior.

Two emerging architectural paradigms, i.e., Software Defined Networking (SDN) and Network Function Virtualization (NFV), enable the deployment and management of Service Function Chains (SFCs). A SFC is an ordered sequence of abstract Service Functions (SFs), e.g., firewalls, VPN-gateways, traffic monitors, that packets have to traverse in the route from source to destination. While this appealing solution offers significant advantages in terms of flexibility, it also introduces new challenges such as the correct configuration and ordering of SFs in the chain to satisfy overall security requirements. This paper presents a formal model conceived to enable the verification of correct policy enforcements in SFCs. Software tools based on the model can then be designed to cope with unwanted network behaviors (e.g., security flaws) deriving from incorrect interactions of SFs in the same SFC.

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 current version of IEEE 802.11, based on EDCA, is unable to support fine-grained assignments of priorities to messages. Instead, such an ability could be advantageous in distributed real-time control systems communicating over the air, as it would enable the exploitation of feasibility analysis to assess whether or not timing constraints are met. In this paper, a proposal is made for implementing a simple fixed-priority access scheme on conventional, commercial Wi-Fi devices. Basically, this is obtained by disabling the random backoff mechanism and suitably managing interframe gaps only. In particular, each real-time message is assigned a unique gap duration, so as to help in preventing collisions. An experimental campaign has been carried out on real devices aimed at assessing the performance this approach can achieve.

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.

Access control is a necessary building block in the security of any kind of cyber system and, in this sense, industrial networked systems (INSs) make no exception. Typically, access control policies are specified at a high implementation-independent level of abstraction and then mapped onto the real system by leveraging available policy enforcement mechanisms. Unfortunately, different from general-purpose ICT systems, enforcement mechanisms are generally very basic in INS. As a consequence, verifying the correctness of policy implementation becomes a crucial task, especially cumbersome when it needs to be carried out entirely by hand. This paper presents a new methodology, which also serves as the basis of a purposely developed software tool conceived to cope with the lack of policy enforcement mechanisms in INS and to allow semiautomatic verification of policy implementation. Our approach is based on a twofold system model that enables both the abstract specification of access control policies and the detailed description of the target physical system. These two separate views are then combined to automatically determine whether the current system implementation matches the policy specification.

The flexibility and reconfigurability requirements of factories and manufacturing plants of the future can be partially met by adopting technologies and solutions already available for testing and experimentation. Openness and adherence to international standards are becoming increasingly important in modern distributed production and automation systems, especially when they have to cope with ever-increasing product differentiations and short product lifecycles. However, the increased flexibility and openness should not come to detriment of the system real-time characteristics. This paper deals with a pilot mechatronic architecture for agile transport systems, which has been specifically developed to enable the study of the aforementioned aspects in the framework of the “Factory of the Future” Italian flagship project. In particular, the paper focuses on possible bottlenecks and pitfalls at the operating system and communication levels, and provides preliminary indications on how to address or mitigate them by means of solutions already available on the market.

The performance of the IEEE 802.11 WLAN are influenced by the wireless channel characteristics that reflect on the signal-to-noise ratio (SNR), particularly in industrial communication systems, that often operate in harsh environments. In order to cope with SNR reductions, the IEEE 802.11 WLAN specification suggests to adapt (reduce) the transmission rate, since the modulation techniques employed at the lower rates are more robust. However, the standard does not define any rate adaptation (RA) technique, leaving the actual implementation to the device manufacturers choice. In this paper we focus on RA techniques for industrial communication systems that are typically subjected to tight reliability and timing requirements. In detail, we compare the performance figures of a general purpose widespread technique, namely the automatic rate fallback (ARF), with those of the RA techniques actually implemented on two commercially available IEEE 802.11 devices via a set of practical experiments. The obtained results show that these techniques are characterized by a relevant number of packet retransmissions that may introduce a considerable randomness on the service time, possibly leading to performance degradation. Consequently, we propose two new techniques and evaluate their behavior by means of numerical simulations carried out for typical industrial traffic profiles. The outcomes are encouraging since the proposed RA techniques show in most cases better performance than ARF.

The problem of enhancing reliability while providing real-time guarantees in industrial communication over wireless networks has been widely addressed by the scientific literature. Several analyses have been carried out that consider this problem in a real-time scheduling framework, modeling both real-time transmission flows and possible retransmissions as a set of periodic tasks. These analyses, however, approach the schedulability problem from a high level point of view, where lower communication layers are modeled as if they were a unique stack that introduces a certain error probability and do not take into account their actual behavior. In this paper, we present an accurate evaluation of the transmission times of the packets belonging to the flows in case of an IEEE 802.11g WLAN is employed at the lower layers. Moreover, we address the negative influence of the wireless network non-deterministic behavior, mainly caused by both backoff procedures and MAC-layer retransmissions, on the feasibility of a flow set providing some possible solutions.

In industrial communication systems, the unavailability of models of real components, in particular of their behavior in the presence of non-ideal channels, often leads to consistent differences between theoretical/simulative analysis and experimental results. In this paper we consider a hybrid (Ethernet/IEEE 802.11) network employing access points from different vendors and measure a specific performance index, namely the service time, for various transmission rates focusing on the effects of both internal component behaviors and channel conditions. The obtained results show how, in case of small payload packets transmitted on noisy channels, the choice of a fixed low transmission rate guarantees better service times. Indeed, decreasing the transmission rate on the wireless segment below 54 Mb/s reveals effective, since it limits the occurrence of packet errors and the consequent retransmissions reducing the service time variability to the intrinsic randomness of the employed devices.

In the last years, several wireless standards have been profitably tested for possible application in factory communication systems, showing encouraging results even in time-critical applications. However, the achieved performance are clearly related to the specific applications considered and, more important, to the specific wireless components employed. In this paper, we consider the wireless extension of a very popular Real-Time Ethernet network, Ethernet Power-link, and we propose a practical implementation of it based on commercially available IEEE 802.11 Access Points. We first provide a theoretical analysis of the expected polling times and then we compare the obtained results with the outcomes of some experimental sessions carried out on a prototype installation, in order to characterize the behavior of the employed devices.

The performance evaluation of wireless networks for industrial applications represents a relevant issue for the scientific community. One of the most important aspects of these activities is concerned with the validation of the theoretical models derived from accurate analysis of the protocols employed by the networks. In this paper we focus on a typical industrial application of the IEEE 802.11 wireless LAN. Particularly, we consider a master-slave protocol and provide an exhaustive analysis of the polling time of a slave station aimed at understanding the effects of the internal delays of the components employed along with their influence on the overall behavior of the networks.

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.

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.

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.

In the last years real-time Ethernet (RTE) networks, based on the IEEE 802.3 protocol, able of providing realtime data transfer have been even more employed by applications at low levels of factory automation systems. In this paper we focus on Ethernet Powerlink, one of the most popular RTE networks included in the IEC 61784 International Standard, which represents the normative reference document for industrial communication systems. We firstly provide a short description of the Ethernet Power-link protocol focusing, in particular, on the handling of both cyclic and acyclic traffic. Subsequently, we propose an alternative technique which allows, in spite of no significant variations of the protocol, to effectively manage real-time acyclic data (e.g. alarms). Finally, we present the results obtained from numerical simulations of the behavior of a specific network configuration implementing the new technique.