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EtherCAT is one of the most prominent representative of Industrial Ethernet communication technology. It provides high real-time performance together with rich functionality set. Some of its important features are very accurate distributed clock (DC) and cable redundancy. These features work perfectly when standalone. However there are some inherent problems when combined. There exist couple of solutions...
In industrial automation, unexpected failures often generate high direct and indirect costs. To achieve high availability, the critical parts of the system are typically redundant. M-out-of-N (MooN) redundancy is a widespread redundancy pattern because it offers low failover times. This pattern has however two major disadvantages. First, the voter, an essential entity in MooN patterns, is itself a...
One of the most important requirements for the industrial networks, apart from the real-time capability, is the reliability. There are several methods that can be used to increase the communication reliability. One of them is data duplication, which is afterwards transmitted using two different (disjoint) paths. Since, such path search for time triggered Ethernet based systems is typically done during...
Network-based clock synchronization is an important prerequisite for many application areas and more and more required for the factory floor for network arbitration, control, and monitoring. Limitations of existing clock synchronization protocols are that they either support high redundancy and robustness or high precision. This paper presents an approach to integrate slave-side robustness into high...
Reliability is a key requirement in many distributed real-time systems deployed in safety and mission critical applications, and temporal redundancy is a widely employed strategy towards guaranteeing it. The temporal redundancy approach is typically based on task re-executions in form of entire tasks, task alternates or, check-pointing blocks, and each of the re-execution strategies have different...
Distributed systems rely in communication networks, typically a bus, in order to exchange messages and fulfill their goals. However, message transmission is subject to interferences that ultimately can lead to message corruption. In systems where a high-reliability is sought, error recovery mechanisms can be deployed in order to give the required reliability level, and this can be done in the spatial...
Fault-tolerance is becoming an increasingly crucial aspect of the design of Networked Control Systems (NCSs) in order to mitigate system downtime. However, the introduction of fault-tolerance is typically associated with significant traffic overhead. In this paper, an optimization to an Ethernet-based network fabric fault-tolerant NCS is proposed. The proposed optimization halves the amount of overhead...
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...
In the context of critical applications there is an increasing interest in having Distributed Embedded Systems (DESs) that are able to operate in dynamic environments, while at the same time reaching a high reliability. The Flexible Time-Triggered communication paradigm (FTT) is designed to support the QoS and real-time requirements of the traffic of these systems. However, FTT does not provide fault...
In safety-critical systems a global high-reliability is sought, including in the communication network when a distributed control system is used. The FlexRay protocol was developed within the automotive industry with the necessary characteristics to respond to the demands of safety-critical applications, e.g. X-by-wire. Nevertheless, the FlexRay protocol does not define a mechanism to guarantee message...
With Audio and Video Bridging (AVB), the Institute of Electrical and Electronics Engineers (IEEE) AVB task group introduced Real-Time capabilities to Ethernet based on IEEE 802 Standards. As AVB was conceived with a focus on home and professional audio and video transmissions, some mandatory aspects for the application in industrial control networks are not covered. Under the name of Time-Sensitive...
This paper presents optimization techniques for implementing software-based redundancy in industrial control devices. Initially, a brief survey of software-based state replication techniques with a special focus on their applicability in industrial control devices is conducted. The scalability, predictability and low latency of the technique are of particular interest in this case. Based on this survey,...
Visual monitoring in wireless sensor networks can provide valuable information of the monitored field, enriching surveillance and control applications. For those networks, however, some active visual sources may fail or run out of energy, potentially degrading the application monitoring quality. Visual sensors may be deployed to monitor a set of targets that are critical for the monitoring tasks of...
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