Traffic class assignment for mixed-criticality frames in TTEthernet

In this paper we are interested in mixed-criticality applications, which have functions with different timing requirements, i.e., hard real-time (HRT), soft real-time (SRT) and functions that are not time-critical (NC). The applications are implemented on distributed architectures that use the TTEthernet protocol for communication. TTEthernet supports three traffic classes: Time-Triggered (TT), where frames are transmitted based on static schedule tables; Rate Constrained (RC), for dynamic frames with a guaranteed bandwidth and bounded delays; and Best Effort (BE), for which no timing guarantees are provided. HRT messages have deadlines, whereas for SRT messages we capture the quality-of-service using "utility functions". Given the network topology, the set of application messages and their routing, we are interested to determine the traffic class of each message, such that all HRT messages are schedulable and the total utility for SRT messages is maximized. For the TT frames we decide their schedule tables, and for the RC frames we decide their bandwidth allocation. We propose aTabu Search-based metaheuristic to solve this optimization problem. The proposed approach has been evaluated using several benchmarks, including two realistic test cases.</jats:p

Mixed-Criticality on the AFDX Network: Challenges and Potential Solutions

In this paper, we first assess the most relevant existing solutions enabling mixed-criticality on the AFDX and select the most adequate one. Afterwards, the specification of an extended AFDX, based on the Burst-Limiting Shaper (BLS), is detailed to fulfill the main avionics requirements and challenges. Finally, the preliminary evaluation of such a proposal is conducted through simulations. Results show its ability to guarantee the highest criticality traffic constraints, while limiting its impact on the current AFDX traffic

Performance impact of the interactions between time-triggered and rate-constrained transmissions in TTEthernet

Switched Ethernet is becoming a de-facto standard in industrial and embedded networks. Many of today's applications benefit from Ethernet's high bandwidth, large frame size, multicast and routing capabilities through IP, and the availability of the standard TCP/IP protocols. There are however many variants of Switched Ethernet networks, just considering the MAC level mechanisms on the stations and communication switches. An important technology in that landscape is TTEthernet, standardized as SAE6802, which allows the transmission of both purely time-triggered (TT) traffic and sporadic (or rate-constrained-RC) traffic. To the best of our knowledge, the interactions between both classes of traffic have not been studied so far in realistic configurations. This work aims to shed some light on the kind of performances, in terms of latencies, jitters and useful bandwidth that can be expected from a mixed TT and RC configuration. The following issues will be answered in a quantified manner by sensitivity analysis: How do both classes of traffic interfere with each other? What are the typical worst-case latencies and useful bandwidth that can be expected for a RC stream for various TT traffic loads? What is the overall impact of TTEthernet integration policy for the RC traffic? This study builds on a worst-case traversal time analysis developed by the authors for SAE6802, and explores these questions by experiments performed configurations of various sizes

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

One solution for TTEthernet synchronization analysis using genetic algorithm

Bezbjednosno-kritični sistemi poput aviona ili automobila zahtijevaju visoko-pouzdanu razmjenu poruka između uređaja u sistemu, što se postiže primjenom determinističkih mreža. Pravilno uspostavljanje međusobne usklađenosti časovnika, kao i konstantno održavanje vremenske usklađenosti, svrstavaju se među najbitnije aspekte determinističkih mreža među kojima su i TTEthernet mreže. Ukoliko časovnici mrežnih uređaja nisu vremenski usklađeni, deterministička razmjena poruka u mreži nije izvodljiva. S obzirom da se informacije o najkritičnijim funkcijama sistema prenose preko determinističke klase poruka, očigledno je da ovakvi servisi neće biti dostupni sve dok se časovnici ne usklade. Teza se bavi procjenom najgoreg slučaja vremena koje je potrebno da protekne da bi se časovnici mrežnih uređaja međusobno uskladili, u slučaju da u mreži postoji jedan uređaj pod otkazom. Procjene su vršene pomoću OMNeT++ simulacija uz primjenu genetskog algoritma. Simulacije pokazuju da se vrijeme neophodno da se uspostavi usklađenost časovnika u TTEthernet mreži značajno povećava pod uticajem uređaja pod otkazom, a samim tim se produžava i vrijeme nedostupnosti najkritičnijih servisa mreže. Simulacije pokazuju da se za mrežu posmatranu u tezi, za izabrane parametre mreže dobija procijenjena vrijednost medijane jednaka 489579μs za najgori slučaj uspostavljanja vremenske usklađenosti u mreži.Safety-critical systems like airplanes and cars demand high-reliable communication between components within the system, which is achieved by using deterministic networks. Proper establishing and maintenance of synchronization of device clocks in the network components represents one of crucial aspects in deterministic networks where belong TTEthernet as well. If device clocks are not synchronized, deterministic communication is not feasible. Keeping in mind that most critical information has been exchanged between the network components using deterministic traffic class, it is obvious that such services will not be available until the clocks in the network are synchronized. The thesis deals with estimation of worst-case startup time for observed TTEthernet network, in case that one device in the network is under failure. The estimation is performed by OMNeT++ simulations and using genetic algorithm. The simulations show that startup time of the network is extended significantly under impact of faulty component. Also, unavailability of most critical services in the network is extended for the same time. For the network simulated in this thesis, estimated median value equals 489579 μs for worst-case startup time