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.
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".[note 1]
- 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.
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.
- The quality of the synchronization determines the limit on the efficiency with which the physical link between a data source and a switch may be used for time-triggered transfers, and thus the overall efficiency of the network: The individual data frames must be transmitted so that they arrive within the time slot expected by the switch. Hence the maximum error in synchronization between the source and the switch must be included in the duration of the time slot that the switch must allow. Otherwise frames of the time-triggered transfer, which are correctly timed from the perspective of the source, will be dropped by the switch for being mistimed. Hence, the larger the errors in the synchronization, the fewer such frames can be transmitted in any given period. This is a particular problem in the use of standard IEEE 802.3 Ethernet network interfaces with software support for IEEE1588 for the transmission of time-triggered transfers, e.g. for provably reliable data transport. This is, partly, why the use of specific TTEthernet network interfaces with hardware support for synchronization, etc., is recommended in implementations of TTEthernet.
- http://www.tttech.com/technologies/ttethernet/, retrieved 13 July 2014.
- "TTEthernet – A Powerful Network Solution for All Purposes" (PDF). Marketing whitepaper. TTTech Computertechnik AG. 2009. Archived from the original (PDF) on March 28, 2014. Retrieved March 28, 2014.
- Wilfried Steiner and Bruno Dutertre, SMT-Based Formal Verification of a TTEthernet Synchronization Function, S. Kowalewski and M. Roveri (Eds.), FMICS 2010, LNCS 6371, pp. 148–163, 2010.
- "New Products: Ethernet Platform". News release in Avionics magazine. April 1, 2008. Retrieved June 9, 2011.
- T. Steinbach, F. Korf, T. C. Schmidt (May 18, 2010). "Comparing time-triggered Ethernet with FlexRay: An evaluation of competing approaches to real-time for in-vehicle networks". 8th IEEE International Workshop on Factory Communication Systems (WFCS): 199–202. doi:10.1109/WFCS.2010.5548606. ISBN 978-1-4244-5460-0.
- Hermann Kopetz; Astrit Ademaj; Petr Grillinger; Klaus Steinhammer (May 2005). "The Time-Triggered Ethernet (TTE) Design". 8th IEEE International Symposium on Object-oriented Real-time distributed Computing. Seattle, Washington: TU Wien: 22–33. doi:10.1109/ISORC.2005.56. Retrieved December 5, 2010.
- Astrit Ademaj; Hermann Kopetz. "Time-Triggered Ethernet and IEEE 1588 Clock Synchronization". International IEEE Symposium on Precision Clock Synchronization for Measurement, Control and Communication. TU Wien: 41–43. doi:10.1109/ISPCS.2007.4383771. Retrieved December 5, 2010.
- AS6802: Time-Triggered Ethernet
- www.tttech.com/ttethernet - TTTech Computertechnik AG
- realtime-ethernet.de - Comparison of realtime-ethernet solutions Explanations partly German, partly English
- Michael Cooney (April 14, 2009). "NASA takes Ethernet deeper into space". Network World. Retrieved June 9, 2011.
- NASA and TTTech partner on space network standards for network centric space operations Military & Aerospace Electronics magazine on TTEthernet
- "TTEthernet Overview". Industry group web site. TTA-Group. Retrieved June 9, 2011.
- "What is SAE AS6802 "Time-Triggered Ethernet"?". Deterministic Ethernet & Unified Networking. Retrieved 31 March 2014.