Time-Triggered Ethernet Research Articles

Optimizing Virtual Network Embedding for Avionics with Time-Triggered Traffic Scheduling

Network virtualization technology abstracts the nodes and links resources in the physical network, and enables multiple virtual networks (VNs) to share the substrate network (SN) resources through the Virtual Netw ork Embedding (VNE) method. For time-triggered Ethernet (TTE) used in avionics, a time-triggered traffic scheduling oriented virtual network embedding (TT-VNE) method is proposed. While meeting the total resource constraints of traditional VNE problem, it ensures the strict periodicity of time-triggered (TT) traffic. During the solution process, the method sorts the virtual nodes according to the TT traffic bandwidth requirements and the total bandwidth requirements of the links connected to the virtual nodes, embeds the virtual nodes using the breadth first search algorithm, and plans the virtual links in candidate shortest path aggregation. If the TT traffic in the current virtual link is not schedulable, the iterative design of local virtual node re embedding and path planning is carried out. The simulation shows that the request acceptance rate of TT-VNE is not lower than that of existing methods, and when the number of virtual network requests in the star topology exceeds 30 , its request acceptance rate is about 14.3%higher than the VNE-NTANRC-D method which only considers the network topology and resource attributes.

Time-triggered scheduling of mixed-critical flows at end-system in asynchronous AFDX avionic network

Avionics Full-DupleX (AFDX) is a switched Ethernet-based network used in modern commercial airplanes for the transmission of command and control avionics flows. These critical flows require deterministic guarantees leading to a lightly loaded network. Aircraft manufacturers envision to carry additional non avionics flows (i.e. video, audio, service) to take advantage of the spare bandwidth. However, it is then compulsory to preserve the real-time guarantees of avionics flows in terms of bounded jitter at the transmitter output and of bounded end-to-end latency. Depending on the type of additional traffic, Quality of Service (QoS) end-to-end guarantees may be offered to the additional flows of lower criticality in terms of reduced delay or bounded jitter for instance. These guarantees can be ensured by scheduling policies at transmitter and switch level. However, an important safety-related constraint is the asynchronous design of avionics distributed systems that prohibits the use of a network-wide synchronization of end systems and switches. Thus, time-triggered networking such as emerging Time-Triggered Ethernet (TTEthernet) or Time-Sensitive Networking (TSN) cannot be leveraged. This paper underlines the benefits of only scheduling flows at the transmitter, which is compatible with the asynchronous safety constraint of avionics systems. We show that it is possible to build a table schedule that carries both critical avionics flows and additional video flows that meet their timing and bandwidth allocation constraints. Therefore, we design scheduling strategies for efficient distribution of flows in the table scheduling whose performance is compared to the optimal schedule minimizing the emission lag of additional flows. Proposed heuristics are constructed such as to favor the network responsiveness for avionics flows thanks to slot over-provisioning. Extensive results on an A350 AFDX industrial configuration show that for a transmitter load of up to 70% of the available bandwidth, the uniform allocation heuristic provides a performance close to optimal in terms of minimum emission lag for additional flows, so offering a practical configuration heuristic to industry.

Design and Performance Testing of a Simulation Model for Time-Triggered Ethernet

Abstract Time-Triggered Ethernet (TTEthernet) is a new hybrid transmission network technology that introduces time-triggered, synchronization, and security mechanisms based on traditional Ethernet. It is difficult to verify the overall performance mechanism of the TTEthernet through manual calculation. Therefore, this paper models the TTEthernet End System and Switch, and simulates the overall performance of the TTEthernet Model based on the OPNET platform. Firstly, this paper introduces the key mechanisms and development status of the TTEthernet. Secondly, the simulation modeling of the TTEthernet End System and Switch are described, and the key technologies within the model are explained; The End system is an important component of the network, responsible for data generation, transmission, and processing. The Switch is responsible for data forwarding and routing, which plays a crucial role in the performance and stability of the network. Finally, the performance of the TTE network model in this article is analyzed through simulation data, verifying the timeliness, determinacy, and reliability of the model. Simulation data shows that the global throughput of the TTE network model in this article is stable at around 70Mbps, the End-to-End Delay of TT services is around 2.5ms, and the packet loss rate is almost zero, which meets the expected results. However, RC and BE services have higher end-to-end latency and packet loss rates than TT services due to their event triggered messages, but they still meet expectations.

Method for Early Diagnosis of Real-Time Traffic Loss with Timeout Monitoring in Software-Configurable Networks

The purpose of the research is to develop the method for early diagnosis of real-time traffic loss with time-out control in software defined networks (SDN).Methods. An overview and description of the transfer of heterogeneous traffic in an Ethernet switch with support for quality of service and Time-Triggered Ethernet technology is given. The functioning of the timeout control blocks for instantaneous removal of a frame from the hard timeout control system and depending on the length of the frame when the idle timeout receiving side is reached is described in detail. These control units are included in the hardware guard of control time-outs for real-time traffic. The work of the switch OpenFlow is described using guard of control time-outs. The formation of time windows of timeouts during frame transmission is described and developed.Results. With the help of the proposed method of early diagnosis of real-time traffic losses with control of timeouts in SDN, a modeling of SDN based on Petri nets and using the CPN Tools modeling package was carried out. The obtained model and experimental results are consistent with the theoretical calculations and the proposed method of transmitting real-time traffic, taking into account its losses in SDN.Conclusion. Using the model, the functional and temporal behavior of the model was investigated; the method was verified using Petri nets. The results were obtained in the form of time diagrams reflecting the work on traffic types in accordance with the proposed method.

Delay Boundary Analysis of RC Flows in the TTE Switch

With the rapid development of advanced driver assistance systems (ADASs) and infotainment systems, automotive networks have higher requirements for bandwidth and real-time than before. Time-triggered Ethernet (TTE) supports real-time time-triggered communication and event-triggered communication coexistence. TTE is used as a backbone network in intelligent connected vehicles to meet the growing real-time and reliability requirements. To design a real-time TTE switch, the time delay of data streams needs to be analyzed. Most of the recent works analyze end-to-end latency, which is usually based on a particular integration policy and ignores the impact of BE flows. In this paper, we analyze the delay bounds of RC flows in the TTE switch using delay reachability techniques. We consider the impacts of TT flows, RC flows and BE flows on RC flows based on three integration policies: shuffling, preemption and timely blocking, respectively. We obtain a secure upper limit of delay through analysis. Experiments illustrate the degree of influence of each factor on the delay bound of RC flow, which provides a reference for the optimal design of the TTE switch in intelligent connected vehicles.

An Infrastructure for Enabling Dynamic Fault Tolerance in Highly-Reliable Adaptive Distributed Embedded Systems Based on Switched Ethernet.

Distributed Embedded Systems (DESs) carrying out critical tasks must be highly reliable and hard in real-time. Moreover, to operate in dynamic operational contexts in an effective and efficient manner, they must also be adaptive. Adaptivity is particularly interesting from a dependability perspective, as it can be used to develop dynamic fault tolerance mechanisms, which, in combination with static ones, make it possible to provide better and more efficient fault tolerance. However, constructing a DES with such complexity presents many challenges. This is because all the mechanisms that support fault tolerance, real-time, and adaptivity must be designed to operate in a coordinated manner. This paper presents the Dynamic Fault Tolerance for Flexible Time-Triggered Ethernet (DFT4FTT), a self-reconfigurable infrastructure for implementing highly reliable adaptive DES. Here, we describe the design of its hardware and software architecture and the main set of mechanisms, with a focus on fault tolerance.

A Hybrid Wired/Wireless Deterministic Network for Smart Grid

With the rapid growth of time-critical applications in smart grid, robotics, autonomous vehicles, and industrial automation, demand for high reliability, low latency and strictly bounded jitter is sharply increasing. High-precision time synchronization communications, such as Time Triggered Ethernet (TTE), have been successfully developed for wired networks. However, the high cost of deploying additional equipment and extra wiring limits the scalability of these networks. Therefore, in this article, a hybrid wired/wireless high-precision time synchronization network based on a combination of high-speed TTE and 5G Ultra-Reliable and Low-Latency Communications (URLLC) is proposed. The main motivation is to comply with the low latency, low jitter, and high reliability requirements of time critical applications, such as smart grid synchrophasor communications. Therefore, in the proposed hybrid network architecture, a high-speed TTE is considered as the main bus (i.e., backbone network), whereas a Precision Time Protocol (PTP) aided 5G-URLLC-based wireless access is used as a sub-network. The main challenge is to achieve interoperability between the PTP aided URLLC and the TTE, while ensuring high precision timing and synchronization. The simulation results demonstrate the impact of the PTP-aided URLLC in maintaining network reliability, latency, and jitter in full coordination with the TTE-network.

The Issues on Time Synchronization Technology in Time Triggered Ethernet

Based on the idea of time-triggered, global unified high precision time synchronization is the foundation of network deterministic communication. In the process of time synchronization, clock synchronization algorithm, transmission delay, clock drift and so on will affect the accuracy of clock synchronization. It is a great technical challenge to realize high precision and reliable clock synchronization. This paper collates and analyses the relevant literature, first introduces the time-triggered Ethernet, then analyses the time synchronization protocol that can be used for high-precision clock synchronization, reviews the development status of time synchronization technology and makes an overall analysis. Finally summarizes the clock synchronization difficulty and prospects the development trend of the time synchronization technology.

Hybrid Scheduling Technology of Time-triggered Ethernet Switches: A Review

Switches are one of the key devices in the time-triggered Ethernet. It is very necessary to design high-performance switches to achieve high real-time data transmission. This article sorts out relevant documents on converters, and first introduces the development of avionics system networks. Then, based on Crossbar’s switch structure and related scheduling algorithms, compare the performance of different algorithms. Compare the performance of different algorithms. Secondly, it introduces the current research methods of TTE switches. Finally, it summarizes the future development direction of time-triggered switching hybrid scheduling technology.

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.

A Mixed-Critical Consistent Update Algorithm in Software Defined Time-Triggered Ethernet Using Time Window

Software Defined Networking (SDN) presents a tremendous opportunity for developing abstract management of network updates. However, network updates introduce challenges in terms of consistency. Many consistent update algorithms are proposed for Ethernet, but there is seldom update algorithm for distributed time-triggered system to satisfy requirements of strict real-time and mixed-critical. The contribution of this paper is to present a distributed update mechanism and a mixed-critical update algorithm for the time-triggered (TT) and rate-constrained (RC) traffics to reduce the memory space complexity, computational time complexity, update time, and keep per-packet consistent strictly. More specifically, consistent update is defined and some basic update algorithms are described. And then a packet-based network model is built to describe network resources. Subsequently, the update mechanism is changed for the TT and RC traffics. Meanwhile, a mixed-critical update algorithm, which contains a time window-based update and a rate-constrained update for TT and RC traffics respectively, is proposed. Whether the mixed-critical update algorithm is consistent updates or not is proved logically. Finally, experiments analyzed the performance of the mixed-critical update algorithm, compared with four conventional updates. The results show that there is no black hole, loop and inconsistent path for the mixed-critical update algorithm. The most important thing is that the memory space complexity is reduced by 19.93% at least, compared with two-phase update. Meanwhile, the computational time complexity and update time are reduced by 17.14% and 7.96% respectively, compared with time-based update. The mixed-critical update algorithm provides a method to optimize policy update tasks for distributed time-triggered system, so as to improve the ability of system reconfiguration.

An approach for integrity assurance in Time-triggered Ethernet

In communication systems, integrity is the ability of a system to detect faults and achieve a fail-safe state during operation, and is one of the important attributes of credibility. Currently, there is no effective integrity assurance mechanism in Time-Triggered Ethernet (TTE). This paper combines the principles of cryptography, designs TTE switch with integrity guarantee mechanism, and builds a simulation platform to verify the design implementation. The simulation results show that the mechanism effectively implements the data integrity guarantee of TTE and improves the reliability of the TTE system.

Static Schedule Generation for Time‐Triggered Ethernet Based on Fuzzy Particle Swarm Optimization

In time-triggered ethernet (TTEthernet), designing and optimizing the static scheduling of TT messages to improve the real-time performance of the whole network control system is important. When there is a high load on TTEthernet network communication, the conventional static scheduling policy introduces certain problems, such as increased packet loss rate, load imbalance, and transmission delay. Meanwhile, basic artificial intelligence algorithms generally features convergence within only a few steps, leading to higher probability to fall into a local optimal solution. To realize these targets, Fuzzy particle swarm optimization (FPSO) based on population diversity is established. By combining Particle swarm optimization (PSO) with a fuzzy algorithm, setting the adjustment of the inertia weight and the regulation of the mutation factor as the controlled variables of the Fuzzy logic controller (FLC), and adjusting the FLC inference rules, a novel static schedule generation for TTEthernet is proposed. Simulation results prove that, compared to the conventional rate-monotonic scheduling algorithm and the PSO algorithm, FPSO has a strong global search capability when the communication of the TTEthernet system is in a high-load state. FPSO improves the load balancing of the network and reduces the transmission delay of TT message packets. FPSO shows excellent ability to optimize scheduling tables and guarantee the real-time performance of the TTEthernet system.

An Application-Level Method of Arbitrary Synchronization Failure Detection in TTEthernet Networks

Precise distributed clock synchronization is important for Time-Triggered Ethernet (TTEthernet) in which fail-arbitrary synchronization failure cannot be treated by existed protocols unless every synchronization node is equipped with a dedicated clock monitoring. A novel method was presented to detect arbitrary synchronization failure by some application-level routines which make distributed decisions mainly by monitoring the protocol control frames (PCFs). An arbitrary failure node can be exactly detected and located by the routine resided on each of the Compression Masters based on the concerned accusation messages sent from Synchronization Masters or Synchronization Clients. The proposed method can make up the weak points on the detection of the arbitrary failure node of the existed fault-tolerant synchronization mechanism and enhance the synchronization node to resist the arbitrary failure for TTEthernet. By our SAL-based model checking, this method had been formally verified to have a fail-arbitrary detection capacity even in a standard integration configuration. Simulations imply that the quality of the whole clock synchronization is effectively improved after the failure node has been isolated.

RC performance analysis based on model optimization with the aid of network calculus

Time-Triggered Ethernet (TTE) Network is a communication network which combines the time-triggered traffic and event-triggered traffic. Based on network calculation, the adopted model in TTE considers the worst case which assumes a number of traffic simultaneously arrive at a node and each virtual link work is fully loaded. Such assumptions lead to the analysis of a certain RC data flow’s delay performance obsessing too much pessimism. In this paper, based on the partition scheduling model, we introduced the loss packet period of the time-triggered data flow $$ p $$ and the correction parameter of rate-constrained (RC) data flow $$ \mu $$ and then optimized the model of service curve and arrival curve of a certain RC data flow. The delay performance of RC data flow is analyzed under proposed optimized model. Simulation results verify that our optimized model relieves the pessimism on delay analysis. The smaller the $$ p $$ value is and the larger the $$ \mu $$ value is, the stricter delay bound can be obtained by our optimized model than by the traditional model. According to the optimized delay analysis model, the scheduling table can be better rearranged and the system resources can be used reasonably.

Network Topology Optimization Based on Time-Triggered DIMA

Distributed Integrated Modular Avionics System (DIMA) has attracted extensive attention in recent years, and the time-triggered Ethernet (TTE) supports the time triggering mechanism of DIMA system, so it has become the main protocol adopted by this system. In order to generate a network topology with lower architecture cost, load balancing and relatively short path, we studied the network topology optimization problem based on TTE. In view of the arbitrariness of TTE network topology, based on the analysis of time-triggered DIMA model, Floyd algorithm and simulated annealing algorithm are applied to realize topology optimization. The simulation results show that the proposed topology design and optimization method can not only effectively reduce network congestion, but also save network cost.

Impact of time-triggered transmission window placement on rate-constrained traffic in TTEthernet networks

Safety-critical Ethernet-based networks are receiving significant attention in avionics, automotive and industrial domains. Time-Triggered Ethernet (TTEthernet AS6802) provides safety-critical transmission guarantees via a high priority, time-triggered (TT) traffic class and a lower priority, rate-constrained (RC) traffic class. TT traffic is transmitted between synchronized nodes of a TTEthernet network in offline scheduled TT transmission windows. In this work, we analyze the impact of different placement strategies for these TT transmission windows on end-to-end delay and jitter of RC messages on the same path segment. We show that, depending on the placement of TT transmission windows in a schedule, the end-to-end delay and jitter of RC messages can vary significantly. We further introduce link-based offsets, a new placement strategy for TT transmission windows which allows to reduce the impact of TT transmission windows on RC traffic. In this strategy offsets are applied to all TT transmission windows in a physical link schedule to reduce the amount of time that an RC message on the same physical link is delayed by TT traffic. The link-based offsets strategy can be implemented in the TTEthernet scheduler and does not require hardware modifications. We show that the link-based offset strategy can reduce the end-to-end delay and jitter of RC traffic, and evaluate our claims using an OMNET++ simulation.

An imporosity message scheduling based on modified genetic algorithm for time-triggered ethernet

An imporosity message scheduling based on modified genetic algorithm for time-triggered ethernet