Time-triggered Messages Research Articles

A Performance Analysis Framework of Time-Triggered Ethernet Using Real-Time Calculus

With increasing demands of deterministic and real-time communication, network performance analysis is becoming an increasingly important research topic in safety-critical areas, such as aerospace, automotive electronics and so on. Time-triggered Ethernet (TTEthernet) is a novel hybrid network protocol based on the Ethernet standard; it is deterministic, synchronized and congestion-free. TTEthernet with a time-triggered mechanism meets the real-time and reliability requirements of safety-critical applications. Time-triggered (TT) messages perform strict periodic scheduling following the offline schedule tables. Different scheduling strategies have an effect on the performance of TTEthernet. In this paper, a performance analysis framework is designed to analyze the end-to-end delay, backlog bounds and resource utilization of network by real-time calculus. This method can be used as a base for the performance evaluation of TTEthernet scheduling. In addition, this study discusses the impacts of clock synchronization and traffic integration strategies on TT traffic in the network. Finally, a case study is presented to prove the feasibility of the performance analysis framework.

Research on Time Triggered Ethernet Scheduling Planning Method

Time-triggered Ethernet adds a time-triggered traffic type based on traditional event-triggered best-effort traffic, which extends data traffic into three communication formats, namely time-triggered (TT) messages and rate-constrained (RC) messages and the best-effort (BE) messages. Aiming at the time-triggered Ethernet message scheduling planning problem, this paper first introduces the principle of the SMT solver and the idea of the solver algorithm, and designs constraints for the message scheduling problem. Based on this, the paper introduces a load balancing strategy and a step-by-step iterative conflict backtracking method, designs and completes a time-triggered Ethernet message scheduling algorithm, and then completes scheduling planning for time-triggered traffic and optimization of scheduling results. For the planning results, the paper proposes verification indicators for network load balancing and algorithm solution efficiency, designs a test set for algorithm verification, completes algorithm analysis and verification based on the test set solution results, and determines the algorithm optimization effect.

Enhancing Real-Time and Determinacy for Network-Level Schedule in Distributed Mixed-Critical System

Time-triggered Ethernet (TTE) is designed as a deterministic real-time network for mixed-critical real-time systems, such as industrial automation, aerospace, and aviation. Due to asynchrony between tasks and the network in end systems (ESes), time-triggered (TT) messages have to spend uncertain time in waiting for being scheduled after they are generated. The waiting time uncertainly increases end to end delays for TT messages and will degrade the real-time and determinacy of TT messages sequentially. The contribution of this paper is to present a new architecture SDTTE to minimize the end to end delays, so as to enhance real-time and determinacy of TT messages. More specifically, a frame-based network model is built to describe distributed network resources. Under the network model, the end to end delay model with asynchrony between tasks and the network is analyzed. To match the generated time with the triggered time for TT messages, the triggered mechanism of the TT traffic in ESes is regarded as event strategy to detect the generated time of TT messages automatically. Based on this, the software defined TTE (SDTTE) is presented to optimize TT schedule online in switches. Furthermore, a simplified algorithm based on Satisfiability Modulo Theories (SMT) is proposed to satisfy real-time computing requirements. Finally, experiments with three network sizes verify the availability of SDTTE and analyze its performance. The results show that end to end delays for TT messages in SDTTE are decreased by about 95% compared with those in TTE. And the delays for rate-constrained and best-effort messages in SDTTE are almost as well as those in TTE. The processing time is less than 10s. In general, SDTTE provides a method to optimize end to end delays for TT messages in TTE, thus SDTTE has more determinacy and real-time than TTE. Meanwhile, SDTTE makes dynamic reconfiguration possible in practice.

JAMS-SG

Time-triggered automotive networks use time-triggered protocols (FlexRay, TTEthernet, etc.) for periodic message transmissions that often originate from safety and time-critical applications. One of the major challenges with time-triggered transmissions is jitter, which is the unpredictable delay-induced deviation from the actual periodicity of a message. Failure to account for jitter can be catastrophic in time-sensitive systems, such as automotive platforms. In this article, we propose a novel scheduling framework (JAMS-SG) that satisfies timing constraints during message delivery for both jitter-affected time-triggered messages and high-priority event-triggered messages in automotive networks. At design time, JAMS-SG performs jitter-aware frame packing (packing of multiple signals from Electronic Control Units (ECUs) into messages) and schedules synthesis with a hybrid heuristic. At runtime, a Multi-Level Feedback Queue (MLFQ) handles jitter-affected time-triggered messages and high-priority event-triggered messages that are scheduled using a runtime scheduler. Our simulation results, based on messages and network traffic data from a real vehicle, indicate that JAMS-SG is highly scalable and outperforms the best-known prior work in the area in the presence of jitter.

Formal Modeling and Verifying the TTCAN Protocol from a Probabilistic Perspective

The time-triggered CAN (TTCAN) protocol has been widely used in the automotive industry to fulfil the safety and real-time requirements of the application. As an extension of the standard CAN protocol, the TTCAN protocol aims to guarantee a safe and deterministic communication by introducing time-triggered messages with respect to a global synchronized time, which are scheduled in independent transmission windows within the system matrix. However, the new features bring more difficulties in designing and verifying the reliable applications in the TTCAN network. In this paper, we first present a formal probabilistic model of the TTCAN protocol with a consideration of its novel features. A TTCAN system consisting of three parts, i.e., a system matrix, an arbitration and some nodes, is modeled as discrete Markov chains model. Furthermore, five probabilistic properties are described and verified in the probabilistic model checker tool PRISM. Our work gives a quantitative analysis method for the given requirements, which facilitates the designers to a formal understanding of TTCAN protocol.

A PCGL-based data loading algorithm for electrical vehicle time-triggered CAN

In this paper, a period correlative group loading (PCGL)-based algorithm is proposed specifically for the real-time communication of random messages in electrical vehicle TTCAN networks. By compressing the bandwidth radio of the synchronous phase, the real-time response of event-triggered messages is accelerated. The PCGL-based scheduling approach will be detailed and described. The proposed method is tested on the scheduling for SAE electrical vehicle message standard and the results show that, on the premise of guaranteeing the real-time efficiency of time-triggered messages, the real-time efficiency of event-triggered messages is significantly improved.

A PCGL-based data loading algorithm for electrical vehicle time-triggered CAN

In this paper, a period correlative group loading (PCGL)-based algorithm is proposed specifically for the real-time communication of random messages in electrical vehicle TTCAN networks. By compressing the bandwidth radio of the synchronous phase, the real-time response of event-triggered messages is accelerated. The PCGL-based scheduling approach will be detailed and described. The proposed method is tested on the scheduling for SAE electrical vehicle message standard and the results show that, on the premise of guaranteeing the real-time efficiency of time-triggered messages, the real-time efficiency of event-triggered messages is significantly improved.

A New Scheduling Method for TTCAN-Based Turbofan Distributed Control System

Abstract A hybrid-scheduling method, consisting of packing algorithm, genetic algorithm and priority promotion algorithm, was proposed for time-triggered CAN in this paper. We divided the basic cycles (BC) into synchronous phase for transmitting time-triggered messages and asynchronous phase for transmitting event-triggered messages. At the each end of BC, fault-tolerant windows were designed to improve the fault-tolerance. The First Fit Increasing and the genetic algorithm scheduled and optimized the transmission of time-triggered messages in the synchronous phase, and the priority promotion algorithm optimized the transmission of event-triggered messages in the synchronous phase. For the communication application of a TTCAN-based turbofan distributed control system, the new scheduling method improved the bandwidth utilization and arbitrary windows utilization to 99% and 9.3%.

Smart Message Schedule Configuration for Static Segment of Flexray

FlexRay is designed to support highly sophisticated interaction among electronic component units in modern automobiles. This protocol supports high data rates, up to 10 Mbit/s, and is a hybrid protocol which divides the time into two segments; static segment and dynamic segment. In static segment the time-triggered messages and in dynamic segment event-triggered messages are scheduled. This paper addresses message scheduling subject to precedence constraints in static segment of FlexRay. Our objective is to obtain optimum and sub-optimum scheduling solutions with respect to minimizing the number of used slots, and subject to the FlexRay specifications. We formulate the optimization problem using Integer Linear Programming, and we present a greedy heuristic which helps to reduce the search space of our optimization and achieves sub-optimal solutions more quickly. Our experiments on a prototypical application from a major automotive OEM demonstrate the efficiency of our proposed approaches.

Timing Analysis of TTEthernet Traffic

Over time, more and more systems are becoming mixed-criticality systems. As the complexity and size of these systems grow, computation/communication resources should be more efficient than with traditional systems. Time-triggered (TT) Ethernet is a communication infrastructure that enables the use of a single physical communication infrastructure for distributed mixed-criticality applications while providing timely determinism. TTEthernet distinguishes between two traffic categories: The standard event-triggered (ET) traffic and the TT traffic. The latter, for which higher priority is granted, is subject to strong timing guarantees because of strict-periodicity constraint which fixes start-time cycles of TT messages. In addition, messages in an ET Ethernet traffic, which are of lower priority, have a minimum time interval between their transmission. The focus of this paper is on the timing analysis of a TTEthernet traffic by proposing: (i) A feasibility condition allowing to assess the timing requirements of TT messages. (ii) A schedulability condition allowing to check the schedulability of ET messages by taking into account of TT messages scheduling and idle times.

An Efficient Message Dissemination Technique in Platooning Applications

Autonomous driving in road trains, a.k.a. platooning, may reduce fuel consumption considerably if the inter-vehicle distances are kept short. However, to do this, the intra-platoon communication must not only be reliable but also able to meet strict deadlines. While time-triggered messages are the foundation of most distributed control applications, platooning is likely to also require dissemination of event-driven messages. While much research work has focused on minimizing the age of periodic messages, state-of-the-art for disseminating event-driven messages is to let all nodes repeat all messages and focus on mitigating broadcast storms. We derive an efficient message dissemination scheme based on relay selection which minimizes the probability of error at the intended receiver(s) for both unicast and broadcast, without degrading the performance of co-existing time-triggered messages. We present a full analysis of the resulting error probability and delay, when relayers, selected by our algorithm, are used to disseminate messages within a platoon. Numerical results indicate that the proposed relaying policy significantly enhances the reliability for a given delay.

Design optimization of TTEthernet-based distributed real-time systems

Many safety-critical real-time applications are implemented using distributed architectures, composed of heterogeneous processing elements interconnected in a network. Our focus in this paper is on the TTEthernet protocol, a deterministic, synchronized and congestion-free network protocol based on the Ethernet standard and compliant with the ARINC 664 Specification Part 7. TTEthernet is highly suitable for safety-critical real-time applications since it offers separation for messages using the concept of virtual links and supports three time-criticality classes: Time-Triggered (TT), Rate-Constrained (RC) and Best-Effort. In this paper we are interested in the design optimization of TTEthernet networks used to transmit real-time application messages. Given the set of TT and RC messages, and the topology of the network, our approach optimizes the packing of messages in frames, the assignment of frames to virtual links, the routing of virtual links and the TT static schedules, such that all frames are schedulable and the worst-case end-to-end delay of the RC messages is minimized. We propose a Tabu Search-based metaheuristic for this optimization problem. The proposed algorithm has been evaluated using several benchmarks.

Design of Reactive Security Mechanisms in Time-Triggered Embedded Systems

In the paper we discuss how a single node communication interface failure in a time-triggered system can be used to model a DoS-type attack. More so, we present a design approach based on active detection of common DoS characteristics, which can serve as a template for attack detection. This approach is feasible in time-triggered systems because of the periodic and deterministic characteristics either at the fieldbus communication or application level. We support our discussion with an example case study of a vehicle braking system implementing time-triggered messages disturbed by fault injection.

Dependable and predictable time-triggered Ethernet networks with COTS components

TTEthernet is a cross-industry communication standard that supports the integration of predictable time-triggered communication and event-triggered standard Ethernet traffic. This paper explores the ability of extending the firmware of Commercial-Off-The-Shelf (COTS) routers in order to support TTEthernet. Thereby, we can achieve a significant cost reduction, upgrade existing infrastructures and make field-failure rates of COTS devices available for certification. Based on a generic model of a COTS router, we introduce four methods for extending a COTS router with support for time-triggered and event-triggered message exchanges. The extended COTS router redirects time-triggered messages within pre-planed time intervals, while also processing event-triggered messages when no time-triggered message are scheduled. We achieve temporal predictability and low jitter by minimizing the effect of event-triggered messages onto the timing of time-triggered messages. Furthermore, experimental results from a prototype implementation provide insight into the performance differences between a COTS router and dedicated hardware.

The TTEthernet synchronisation protocols and their formal verification

TTEthernet is a communication platform for critical, distributed computer-based systems. NASA has selected one of TTEthernet%s high-end configurations for the Orion programme. In other configurations, TTEthernet implements the communication backbone of new energy machineries such as wind turbines. One of TTEthernet's unique features is the integration of applications with differing latency, jitter, and fault-tolerance requirements in a single physical Ethernet network, thereby significantly reducing the amount of wiring in a distributed system. The most critical applications can communicate using time-triggered messages for which a fault-tolerant high-precision network-wide timebase is required. Formal methods are key in the design of protocols that establish and maintain such a timebase and, thus, have been heavily used already during the design phase of TTEthernet. This paper summarises the formal analysis and verification activities of the TTEthernet synchronisation protocols and discusses protocol updates implemented in the TTEthernet standard SAE AS6802.

Message scheduling with reduced matrix cycle and evenly distributed sparse allocation for time-triggered CAN

Controller Area Network (CAN) was initially developed as an in-vehicle real-time communication bus. Due to its low cost and high reliability, it has also become a widely accepted standard in industrial distributed control applications. The CAN protocol has an event-triggered architecture. Although its priority based medium access mechanism provides guaranteed immediate access for the highest priority messages, it may cause unpredictability in communication media for the lower priority messages. In order to address the problems caused by the event-triggered architecture, different time-triggered network architectures, such as TTP, Byteflight, and Flexray, have been introduced. This paper focuses on time-triggered CAN (TTCAN), which is built on the existing CAN standard with the addition of time division multiple access (TDMA). In order to combine the advantages of the event-triggered and time-triggered communication to meet the requirements of the distributed real-time systems, it is crucial to construct feasible message schedules. In this study, a schedule construction method, based on the reduced matrix cycle and evenly distributed sparse allocation, is introduced to produce the best optimum message schedules possible in terms of the message delay performance. The simulation results show that the method introduced in this study provides significant performance improvement not only for the time-triggered messages but also for the event-triggered messages.

Application and Performance Analysis of Dynamic-planning-based Flexible Time Triggered Controller Area Network

To meet the requirement of automotive intelligentizing,the next step in the direction of automotive bus is to support both time-and event-triggered communication services and to attain more flexible of design and scheduling.But controller area network (CAN) protocol is inefficient for time-triggered messages,while time-triggered controller area network (TTCAN) can efficiently fulfill joint support for both event- and time-triggered traffic but lacks flexibility in message scheduling.To these questions,a new dynamic planning-based protocol that is flexible in time-triggered controller area network (FTTCAN) is analyzed.And the elemen- tary cycle comprising of two phases and real-time analysis method for communications of messages in the two phases are explained. Then an FTTCAN-bus system of electric vehicle based on FTTCAN protocol is designed,and the scheduling strategy of signals based on dynamic planning is adopted.And performance analysis of the new system is carried out by comparing with CAN system. Finally,operation test of FTTCAN protocol is carried out on CAN bus development system.The comparison and test results verify that FTrCAN is a good way to design automotive bus system,which can meet the requirements of supporting both time-and event-triggered communication services and being flexible in design and scheduling.

High Level 객체 지향에서 실시간 시뮬레이션 프로그램과 TMO 설계

The object-oriented (OO) distributed real-time (RT) programming movement started in 1990´s and is growing rapidly at this turn of the century. Distributed real-time simulation is a field in its infancy but it is bounded to receive steadily growing recognition for its importance and wide applicability. The scheme is called the distributed time-triggered simulation scheme which is conceptually simple and easy to use but widely applicable. A new generation object oriented (OO) RT programming scheme is called the time-triggered message triggered object(TMO) programming scheme and it is used to make specific illustrations of the issues. The TMO structuring scheme is a general-style components structuring scheme and supports design of all types of component including hard real time objects and non real time objects within one general structure.