Synchronous programming of reactive systems

Reactive systems are computing systems which are interactive, such as real-time systems, operating systems, concurrent systems and control systems. These are among the most difficult computing systems to program. Temporal logic is a formal tool/language which yields excellent results in specifying reactive systems, and this volume (the first of two), offers an introduction to temporal logic and to the computational model for reactive programs which has been developed by the authors.

: This research is directed towards the implementation of a comprehensive toolkit for the development and verification of high assurance reactive systems, especially concurrent, real time, and hybrid systems. For this, we have designed and implemented the STeP (Stanford Temporal Prover) verification system. STeP is a tool for the computer aided formal verification of reactive systems, including real time and hybrid systems based on their temporal specification. STeP integrates model checking and deductive methods to allow the verification of a broad class of systems, including parameterized (N component) circuit designs, parameterized (N process) programs. and programs with infinite data domains.

Cyber-physical systems are realized as those systems where the computation, communication and physical processes interact with each other (e.g., robotic systems, automotives, etc). A large class of cyber-physical systems are associated with strict timeliness requirements. They are known as ‘real-time systems’ (e.g., smart grids, avionics, etc). Industrial control systems (ICS) are real-time systems that consist of several closed-loop controls. The main components of a control loop are — a physical plant, sensors, actuators and a controller. The sensors transmit the measurement data to the controller that generates appropriate control signals to actuate the physical plant. Large-scale wireless sensor actuator networks form the main communication framework among the network devices in ICS. Most of the communications between each of these devices are periodic real-time flows with hard deadlines. To ensure reliability, the communication in these systems are time-division multiple access (TDMA) based. Dedicated network resources (time-slots and frequencies) are allocated to these devices in advance and the communication schedule is pre-computed to satisfy the hard deadlines of the real-time flows. The same schedule is repeated over time which makes the schedule predictable in nature. However, a malicious attacker can exploit this predictable time-slots in the schedules to launch timing attacks. Since these applications are time-critical, timing attacks can completely undermine the system performance leading the system to an unsafe state. Schedule randomization is a popular defense mechanism to mitigate timing attacks. Although a few works exist in the literature that use schedule randomization as a countermeasure against timing attacks in real-time uniprocessor systems, none of them are applicable for real-time wireless networks. Schedule randomization as a countermeasure against timing attacks in real-time wireless networks remained largely unexplored. With this objective in focus, this thesis addresses some schedule randomization techniques to mitigate timing attacks in real-time wireless networks. Among the existing wireless network protocols that are in use, the WirelessHART is the most suitable and widely adopted protocol in ICS. A WirelessHART protocol supports centralized architecture, TDMA based communication, multiple channels, etc. All of these characteristics of a WirelessHART network facilitate reliable and predictable communication with real-time flow guarantees in ICS. However, the predictable communication exposes the system to timing attacks, such as selective jamming attacks. Selective jamming attacks are stealthy attacks, however, it can lead the system to an unstable state and can disrupt the safety of the system. As a countermeasure against such attack in WirelessHART network, we propose a centralized schedule randomization technique that randomizes the time-slots and channels in the schedule over every hyperperiod (least common multiple of the periods of the real-time flows) without violating the hard deadlines of the real-time flows, while still satisfying the feasibility constraints of a schedule in a WirelessHART network. The centralized technique generates the schedules offline and distributes the schedules online, hence, cannot support any change in topology in the network. Further, this technique has energy overheads in distributing the schedules to all the network devices at runtime. Hence, we propose a distributed online schedule randomization technique that can generate random feasible schedules at runtime in each network device without affecting the closed-loop control stability. To increase the extent of randomization of time-slots in the schedules, this online distributed technique adopts a period adaptation strategy that can adjust the transmission periods of the real-time flows at runtime depending on the stability of the closed-loop controls. To support an ever-growing number of devices and dense connectivity, the fifth generation (5G) cellular networks is expected to serve as the main communication standard in the future wireless sensor networks. Among the different service categories supported by 5G, the ultra-reliable low-latency communication (URLLC) is mostly suitable for time-critical applications such as the ICS. The communication in 5G is organized into slots over multiple frequencies. To satisfy the hard deadlines of the URLLC flows in ICS, a part of the resources (slots and frequencies) in 5G are reserved for URLLC traffic and the same schedule is repeated over time. The repetition of the same schedule over time makes the slots in the schedules predictable. This, in turn, makes the 5G networks vulnerable to timing attacks. However, the proposed schedule randomization techniques for WirelessHART networks are not applicable for dynamic networks like 5G where the number of flows and the amount of available network resources for URLLC flows vary at runtime. Moreover, the feasibility of the real-time flows need to be guaranteed at runtime. Hence, we propose an online schedule randomization technique that randomizes the slots and the frequencies of the periodic URLLC flows while guaranteeing the feasibility of the flows at runtime.

Industrial Process Measurement and Control Systems are used in most of the industrial sectors to achieve production improvement, process optimization and time and cost reduction. Integration, reuse, flexibility and optimization are demanded to adapt to a rapidly changing and competitive market. In fact, standardization is a key goal to achieve these goals. The international standardization efforts have lead to the definition of the IEC 61131 standard. Part 3 of this standard defines a software model for defining automation projects as well as 5 programming languages. Nowadays, a major part of Programmable Logic Controllers (PLC) vendors follows this standard, although each programming tool adds particularities and stores the automation project in different manner. But, although they may use the same software model and the same programming languages, source code reuse is not available. This work presents an infrastructure that allows transferring source code from one PLC programming tool to any other transparently to the users. The proposal consists of a textual expression of the software model and the programming languages, as well as the mechanisms, based on XML technologies, to achieve tool interoperability.

The specification of reactive and real-time systems must be supported by formal, mathematically-founded methods in order to be satisfactory and reliable. Temporal logics have been used to this end for several years. Temporal logics allow the specification of system behavior in terms of logical formulas, including temporal constraints, events, and the relationships between the two. In the last ten years, temporal logics have reached a high degree of expressiveness. Most of the temporal logics proposed in the last few years can be used for specifying reactive systems, although not all are suitable for specifying real-time systems. In this paper we present a series of criteria for assessing the capabilities of temporal logics for the specification, validation, and verification of real-time systems. Among the criteria are the logic's expressiveness, the logic's order, presence of a metric for time, the type of temporal operators, the fundamental time entity, and the structure of time. We examine a selection of temporal logics proposed in the literature. To make the comparison clearer, a set of typical specifications is identified and used with most of the temporal logics considered, thus presenting the reader with a number of real examples.

IEC61499 Service Interface Function Blocks to Access Decentralized Peripherals with Profibus DP

Real-time systems are those systems in which the correctness of the system depends not only on the logical results of computation but also on the time at which the results are produced [Stankovic 1988]. They span a broad spectrum of complexity from very simple microcontrollers in embedded systems (a microprocessor controlling an automobile engine) to highly sophisticated, complex, and distributed systems (air traffic control for the continental United States). Other real-time systems include command and control systems, process control systems, and multimedia and high-speed communication systems. Some real-time systems are beginning to add expert systems and other AI technology, creating additional requirements and complexities. At least three major trends in the real-time and embedded systems field have had a major impact on its technology: the increased growth and sophistication of embedded systems, the development of more scientific and technological results for hard real-time systems, and the advent of distributed multimedia. Most embedded systems consist of a small microcontroller and limited software situated within some product such as a microwave oven or automobile. However, with the increasing sophistication of such systems, powerful microcontrollers and digital signal processing (DSP) chips are commonly used, as are off-the-shelf real-time operating systems and design and debugging tools. Many people working with embedded systems deal on a daily basis with sensors and data acquisition technology and systems; others construct architectures based on single-board computers (many are still 68000-based, but RISC processors are being used more and more) and buses such as the VME bus. Many people are involved with the programming and debugging of embedded systems, largely using the C programming language and cross development and debugging platforms. Embedded systems may or may not have real-time constraints. Hard real-time systems are those in which missing an important deadline can cause severe consequences, even death. In this area, many fundamental results have been developed. For example, in real-time scheduling, rate monotonic analysis has enabled careful evaluation of many practical systems; the concept and analysis of competitive algorithms has provided important scheduling bounds and limits; and on-line planning has added flexible and dynamic capabilities to real-time systems. Operating systems research has produced predictable primitives, time-constrained synchronization techniques, and reservation and admission-control paradigms. Many other results exist in real-time architecture, fault tolerance, communication protocols, specification and design tools, formal verification, databases and object-oriented systems. Emphasis on all these areas is expected to increase in the foreseeable future. Many hard real-time systems are embedded systems. Distributed multimedia have produced a new set of soft real-time requirements. Real-time principles lie at the heart of distributed multimedia, but without the concomitant high reliability

In the automated Industrial Control System (ICS) where advanced technology is being integrated with core infrastructure, technology development is ahead of the application of security solutions. Our city, power, and transportation control systems are getting smarter and more efficient, but new connectivity and interoperability are making them more vulnerable than ever before. Accordingly, various studies have been conducted for anomaly detection in ICS. In this paper, we propose an unsupervised stacked bidirectional Long Short-Term Memory (LSTM) model for automated anomaly detection in large-scale ICS and introduce a method for performance improvement. In addition, it was written based on participation in HAICon2020, an ICS security threat detection contest hosted by the National Security Research Institute. We use the HAI 2.0 dataset published at HAICon2020 and use Time-series Aware Precision and Recall (TaPR), which is suitable for anomaly detection evaluation in ICS. As a result of submission of test data, we were awarded 2nd place at HAICon2020. We have detected anomalies in ICS. As a follow-up work, we will do further research to identify the sensor and actuator that caused the anomaly and to quickly respond and recover.

Internet-based control systems have been evolving rapidly in recent years. Using Web-based technology, control systems have been shown to have an increasing potential for remote control, industry process control system. In order to improve the industry process system performance affected by Internet-induced variable time delay, this paper carries on a plenty of test: (1) analyzes its statistic characteristics; (2) adopts the modified Elman NN to predict uncertain Internet time-delays; and, (3) applies to adaptive Smith compensator to improve the system dynamic performance and remain system's stability. The experimental tests show that this method improves greatly the forecast precision and system's dynamic performance.

An integrated supervision & control system is the most critical segment in urban rail transit. Particularly, in recent years, the importance of supervision & control systems is also more and more evident with fast development of cloud-platform information processing technology and unattended driving technology in urban rail transit. As important infrastructure in urban rail transit, it is independently equipped and independently managed in actual application and has caused extreme impact on enhancement of operational levels. Based on conventional distribution of integrated supervision & control systems in urban transit, the article herein introduces cloud-platform information processing technology and analyzes requirements on in-depth combination of the automatic supervision system (ATS) related to an unattended driving system of signaling and an integrated supervision & control system, performs optimization design of integrated supervision & control system distribution from perspectives of investment reduction, resource sharing, operation & maintenance costs, and in-depth combination, etc. and describes distribution schemes and concepts of the Traffic Integrated Automated Supervision based on a Cloud platform (TIAS-C). Through comparison of the TIAS-C and the conventional ISCS, the advantages of intelligentization and high informationalization of cloud calculation are better understood, which will create conditions for in-depth combination of a train supervision system with an integrated supervision & control system.KeywordsUrban rail transitIntegrated supervision and control SystemSystem distributionCloud platformAutomatic supervision systemTraffic integrated automated supervision based on a cloud platformUnattended train operation

In this paper, the authors explore the usefulness of a combination of semi-formal and formal methods in specifying reactive systems and verifying their properties. The authors propose an approach combining STATEMATE and the temporal logic FNLOG. STATEMATE is a semi-formal method, which has been used for the development of large industrial applications. It pertains to the specification and design of complex reactive systems and builds simulations and prototypes rapidly. Though STATEMATE provides rigorous specifications, these are not verifiable to ensure and guarantee the reliability of the system being developed. To fulfil the verification objective, a STATEMATE specification is translated into a logic based specification language FNLOG, which allows its verification. This paper describes the cross reference between STATEMATE and FNLOG features. Systematic derivation schemes from STATEMATE models to FNLOG specifications and different steps of the proposed translation procedure.

An architecture for metamorphic control of holonic manufacturing systems

Control systems for industrial processes are more and more using PC-based platforms instead of dedicated devices such as controllers or PLCs. Software packages allow running a "soft PLC" on a normal PC with a general purpose operating system. These solutions present several advantages in terms of flexibility, communications, multi-vendor interfacing, and costs. On the other hand the use of multi-tasking operating systems does not guarantee a-priori respect of the time constrains that control applications present. The paper describes a procedure for measuring the time performances of a soft-PLC with different configurations and loading. Results of preliminary measures are presented and discussed.

The implementation of automated regulatory control has been around since the middle of the last century through analog means. It has allowed engineers to operate the plant more consistently by focusing on overall operations and settings instead of individual monitoring of local instruments (inside and outside of a control room). A similar approach is proposed for cyber security, where current border-protection designs have been inherited from information technology developments that lack consideration of the high-reliability, high consequence nature of industrial control systems. Instead of an independent development, however, an integrated approach is taken to develop a holistic understanding of performance. This performance takes shape inside a multiagent design, which provides a notional context to model highly decentralized and complex industrial process control systems, the nervous system of critical infrastructure. The resulting strategy will provide a framework for researching solutions to security and unrecognized interdependency concerns with industrial control systems.

There is a large number of complex software systems that have reactive behavior. As for any other software system, reactive systems are subject to evolution demands. This paper defines a set requirements that must be fulfilled so that reuse of reactive software systems can be increased. Detailed analysis of a set of representative languages reveals that these requirements are not completely fulfilled by the current programming languages and as such reuse of reactive systems remains a challenge. This paper explains Event Composition Model and its implementation the EventReactor language, which fulfill the requirements. By means of an example, the suitability of the EventReactor language in creating reusable reactive systems is illustrated.