Design Optimization of Cyber-Physical Distributed Systems using IEEE Time-sensitive Networks (TSN)

In this paper we are interested in safety-critical real-time applications implemented on distributed architectures supporting the Time-SensitiveNetworking (TSN) standard. The ongoing standardization of TSN is an IEEE effort to bring deterministic real-time capabilities into the IEEE 802.1 Ethernet standard supporting safety-critical systems and guaranteed Quality-of-Service. TSN will support Time-Triggered (TT) communication based on schedule tables, Audio-Video-Bridging (AVB) flows with bounded end-to-end latency as well as Best-Effort messages. We first present a survey of research related to the optimization of distributed cyber-physical systems using real-time Ethernet for communication. Then, we formulate two novel optimization problems related to the scheduling and routing of TT and AVB traffic in TSN. Thus, we consider that we know the topology of the network as well as the set of TT and AVB flows. We are interested to determine the routing of both TT and AVB flows as well as the scheduling of the TT flows such that all frames are schedulable and the AVB worst-case end-to-end delay is minimized. We have proposed an Integer Linear Programming (ILP) formulation for the scheduling problem and a Greedy Randomized Adaptive Search Procedure (GRASP)-based heuristic for the routing problem. The proposed approaches have been evaluated using several test cases

Simulation of Mixed Critical In-vehicular Networks

Future automotive applications ranging from advanced driver assistance to autonomous driving will largely increase demands on in-vehicular networks. Data flows of high bandwidth or low latency requirements, but in particular many additional communication relations will introduce a new level of complexity to the in-car communication system. It is expected that future communication backbones which interconnect sensors and actuators with ECU in cars will be built on Ethernet technologies. However, signalling from different application domains demands for network services of tailored attributes, including real-time transmission protocols as defined in the TSN Ethernet extensions. These QoS constraints will increase network complexity even further. Event-based simulation is a key technology to master the challenges of an in-car network design. This chapter introduces the domain-specific aspects and simulation models for in-vehicular networks and presents an overview of the car-centric network design process. Starting from a domain specific description language, we cover the corresponding simulation models with their workflows and apply our approach to a related case study for an in-car network of a premium car

Modeling and Analysis of Mixed Synchronous/Asynchronous Systems

Practical safety-critical distributed systems must integrate safety critical and non-critical data in a common platform. Safety critical systems almost always consist of isochronous components that have synchronous or asynchronous interface with other components. Many of these systems also support a mix of synchronous and asynchronous interfaces. This report presents a study on the modeling and analysis of asynchronous, synchronous, and mixed synchronous/asynchronous systems. We build on the SAE Architecture Analysis and Design Language (AADL) to capture architectures for analysis. We present preliminary work targeted to capture mixed low- and high-criticality data, as well as real-time properties in a common Model of Computation (MoC). An abstract, but representative, test specimen system was created as the system to be modeled

Just a Second -- Scheduling Thousands of Time-Triggered Streams in Large-Scale Networks

Deterministic real-time communication with bounded delay is an essential requirement for many safety-critical cyber-physical systems, and has received much attention from major standardization bodies such as IEEE and IETF. In particular, Ethernet technology has been extended by time-triggered scheduling mechanisms in standards like TTEthernet and Time-Sensitive Networking. Although the scheduling mechanisms have become part of standards, the traffic planning algorithms to create time-triggered schedules are still an open and challenging research question due to the problem's high complexity. In particular, so-called plug-and-produce scenarios require the ability to extend schedules on the fly within seconds. The need for scalable scheduling and routing algorithms is further supported by large-scale distributed real-time systems like smart energy grids with tight communication requirements. In this paper, we tackle this challenge by proposing two novel algorithms called Hierarchical Heuristic Scheduling (H2S) and Cost-Efficient Lazy Forwarding Scheduling (CELF) to calculate time-triggered schedules for TTEthernet. H2S and CELF are highly efficient and scalable, calculating schedules for more than 45,000 streams on random networks with 1,000 bridges as well as a realistic energy grid network within sub-seconds to seconds

Intégration itérative des systèmes avioniques communicants en mode synchrone et asynchrone

Les systèmes avioniques modernes sont des systèmes distribués complexes et évolutifs. Ces systèmes sont conçus d’une manière itérative en intégrant à chaque itération une ou plusieurs fonctionnalités. L’ajout de nouvelles fonctionnalités impose des coûts supplémentaires de reconfiguration de telle sorte que l’ensemble du système soit conforme aux exigences temps-réel. Ces systèmes reposent également sur l’adoption d’un protocole de communication déterministe tel que le protocole AFDX. Ce dernier est utilisé dans les avions modernes tels que l’A380 de Airbus et le B787 de Boeing. Il repose sur une communication asynchrone avec limitation de la bande passante. Ce mécanisme permet d’assurer des délais finis de communication. La recherche de plus de déterminisme a poussé la communauté scientifique à chercher d’autres alternatives à AFDX. Le standard Time-triggered Ethernet constitue une bonne alternative. En plus de la communication asynchrone à bande passante limitée, il définit également une communication synchrone. Suivant le type de communication, les approches de vérification des exigences temps-réel diffèrent. Pour analyser les flux asynchrones, on utilise principalement des approches analytiques. Elles assurent un bon compromis entre performance et pessimisme. Pour les flux synchrones, on s’appuie plutôt sur le formalisme de contraintes pour synthétiser un ordonnancement faisable. La combinaison des deux flux constitue un défi en termes de vérification. De plus, les approches de vérification définies ne modélisent ni l’aspect évolutif ni la notion coût.----------ABSTRACT: Modern avionics systems are complex and evolving distributed ones. They are designed iteratively by integrating at each iteration one or more functionalities. Adding new functionality may impose additional reconfiguration costs so that the whole system complies with the realtime requirements. These systems also rely on the adoption of a deterministic communication protocol such as AFDX. The latter is used in modern aircrafts such as the Airbus A380 and the Boeing B787. It relies on asynchronous communication with bandwidth limitations. This mechanism ensures finite communication delays. The search for more determinism encourage the scientific community to look for other alternatives to AFDX. The Time-triggered Ethernet standard is a good alternative. In addition to asynchronous communication with limited bandwidth, it also defines synchronous ones. Depending on the type of communication, verification approaches of real-time requirements differ. To analyze asynchronous flows, we mainly use analytical approaches. They ensure a good compromise between performance and pessimism. For synchronous flows, we rely instead on constraint formalism to synthesize a feasible scheduling. The combination of the two flows is a challenge in terms of verification. In addition, defined verification approaches do not model neither the evolving aspect nor the cost concept

Determinism Enhancement and Reliability Assessment in Safety Critical AFDX Networks

RÉSUMÉ AFDX est une technologie basée sur Ethernet, qui a été développée pour répondre aux défis qui découlent du nombre croissant d’applications qui transmettent des données de criticité variable dans les systèmes modernes d’avionique modulaire intégrée (Integrated Modular Avionics). Cette technologie de sécurité critique a été notamment normalisée dans la partie 7 de la norme ARINC 664, dont le but est de définir un réseau déterministe fournissant des garanties de performance prévisibles. En particulier, AFDX est composé de deux réseaux redondants, qui fournissent la haute fiabilité requise pour assurer son déterminisme. Le déterminisme de AFDX est principalement réalisé par le concept de liens virtuels (Virtual Links), qui définit une connexion unidirectionnelle logique entre les points terminaux (End Systems). Pour les liens virtuels, les limites supérieures des délais de bout en bout peuvent être obtenues en utilisant des approches comme calcul réseau, mieux connu sous l’appellation Network Calculus. Cependant, il a été prouvé que ces limites supérieures sont pessimistes dans de nombreux cas, ce qui peut conduire à une utilisation inefficace des ressources et augmenter la complexité de la conception du réseau. En outre, en raison de l’asynchronisme de leur fonctionnement, il existe plusieurs sources de non-déterminisme dans les réseaux AFDX. Ceci introduit un problème en lien avec la détection des défauts en temps réel. En outre, même si un mécanisme de gestion de la redondance est utilisé pour améliorer la fiabilité des réseaux AFDX, il y a un risque potentiel souligné dans la partie 7 de la norme ARINC 664. La situation citée peut causer une panne en dépit des transmissions redondantes dans certains cas particuliers. Par conséquent, l’objectif de cette thèse est d’améliorer la performance et la fiabilité des réseaux AFDX. Tout d’abord, un mécanisme fondé sur l’insertion de trames est proposé pour renforcer le déterminisme de l’arrivée des trames au sein des réseaux AFDX. Parce que la charge du réseau et la bande passante moyenne utilisée augmente due à l’insertion de trames, une stratégie d’agrégation des Sub-Virtual Links est introduite et formulée comme un problème d’optimisation multi-objectif. En outre, trois algorithmes ont été développés pour résoudre le problème d’optimisation multi-objectif correspondant. Ensuite, une approche est introduite pour incorporer l’analyse de la performance dans l’évaluation de la fiabilité en considérant les violations des délais comme des pannes.----------ABSTRACT AFDX is an Ethernet-based technology that has been developed to meet the challenges due to the growing number of data-intensive applications in modern Integrated Modular Avionics systems. This safety critical technology has been standardized in ARINC 664 Part 7, whose purpose is to define a deterministic network by providing predictable performance guarantees. In particular, AFDX is composed of two redundant networks, which provide the determinism required to obtain the desired high reliability. The determinism of AFDX is mainly achieved by the concept of Virtual Link, which defines a logical unidirectional connection from one source End System to one or more destination End Systems. For Virtual Links, the end-to-end delay upper bounds can be obtained by using the Network Calculus. However, it has been proved that such upper bounds are pessimistic in many cases, which may lead to an inefficient use of resources and aggravate network design complexity. Besides, due to asynchronism, there exists a source of non-determinism in AFDX networks, namely frame arrival uncertainty in a destination End System. This issue introduces a problem in terms of real-time fault detection. Furthermore, although a redundancy management mechanism is employed to enhance the reliability of AFDX networks, there still exist potential risks as pointed out in ARINC 664 Part 7, which may fail redundant transmissions in some special cases. Therefore, the purpose of this thesis is to improve the performance and the reliability of AFDX networks. First, a mechanism based on frame insertion is proposed to enhance the determinism of frame arrival within AFDX networks. As the network load and the average bandwidth used by a Virtual Link increase due to frame insertion, a Sub-Virtual Link aggregation strategy, formulated as a multi-objective optimization problem, is introduced. In addition, three algorithms have been developed to solve the corresponding multi-objective optimization problem. Next, an approach is introduced to incorporate performance analysis into reliability assessment by considering delay violations as failures. This allowed deriving tighter probabilistic upper bounds for Virtual Links that could be applied in AFDX network certification. In order to conduct the necessary reliability analysis, the well-known Fault-Tree Analysis technique is employed and Stochastic Network Calculus is applied to compute the upper bounds with various probability limits