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TTEthernet

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TTEthernet (Time-Triggered Ethernet or TTE) is a computer network technology marketed by TTTech Computertechnik AG "for safety-related applications primarily in transportation industries and industrial automation." and standarized by SAE International as SAE AS6802.

Contents

Description

TTEthernet expands classical Ethernet with services to meet time-critical, deterministic or safety-relevant conditions. It claims to be compatible with IEEE 802.3 standards and integrate with other Ethernet networks. Three message types are provided:

  • Time-triggered messages are sent over the network at predefined times and take precedence over all other message types. The occurrence, temporal delay and precision of time-triggered messages are predefined and guaranteed. The messages have as little delay on the network as possible and their temporal precision is as accurate as necessary. However, "synchronized local clocks are the fundamental prerequisite for time-triggered communication".
  • Rate-constrained messages are used for applications with less stringent determinism and real-time requirements. These messages guarantee that bandwidth is predefined for each application and delays and temporal deviations have defined limits.
  • Best-effort messages follow the usual Ethernet policy. There is no guarantee whether and when these messages can be transmitted, what delays occur and if messages arrive at the recipient. Best-effort messages use the remaining bandwidth of the network and have lower priority than the other two types.

    • This compares to the eight quality of service classes defined by the IEEE P802.1p task group in 1998 and IEEE 802.1Q added to the standard protocol. In 2008 the company announced Honeywell would apply the technology to applications in the aerospace and automation industry. In 2010 a switch-based implementation was shown to perform better than shared bus systems such as FlexRay for use in automobiles.

    Fault-tolerance

    One main point of TTEthernet is to integrate a model of fault-tolerance and failure management. Through a structure of evaluating the risk for each switch and message, it can implement a reliable redundancy management and virtual link integration to assure message transmission even in case of a switch failure. As it is not dynamically-computed routing like in classical Ethernet context, this fault-tolerance system integrated the statically-defined path mechanic found in real-time networks.

    TTEthernet versus TT-Ethernet

    The academic TT-Ethernet project was a joint research project between the Vienna University of Technology and TTTech. First results were published in 2005. The project proposed a preemptive switch and built a prototype for 100 Megabit/second links in 2007. This switch identified the reception of a time-triggered message based on an identifier within the message and preempted other messages under transmission to free the outgoing ports for the time-triggered message.

    Research continued within a joint industrial development between TTTech and Honeywell. TTEthernet was the industrial further development of the research. Objectives were extended towards scalable fault-tolerance and a finer classification of event-triggered messages into rate-constrained and best-effort traffic classes.

    References

    TTEthernet Wikipedia
    (Text) CC BY-SA


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