TTEthernet (Time-Triggered Ethernet)
The TTEthernet (SAE AS6802) standard defines a fault-tolerant synchronization strategy for building and maintaining synchronized time in Ethernet networks, and outlines mechanisms required for synchronous time-triggered packet switching for critical integrated applications. SAE International has released SAE AS6802 in November 2011. 1)
Time-Triggered Ethernet network devices are Ethernet devices which at least implement:
• SAE AS6802 synchronization services for advanced integrated architectures, fail-operational and safety-critical systems
• time-triggered traffic flow control with traffic scheduling
• per-flow policing of packet timing for time-triggered traffic
• robust internal architecture with traffic partitioning
TTEthernet network devices are standard Ethernet devices with additional capability to configure and establish robust synchronization, synchronous packet switching, traffic scheduling and bandwidth partitioning, as described in SAE AS6802. If no time-triggered traffic capability is configured or used, operate as full duplex switched Ethernet devices compliant with IEEE802.3 and IEEE802.1 standards.
In addition, such network devices implement other deterministic traffic classes to enable mixed-criticality Ethernet networking. Therefore, TTEthernet networks are designed to host different Ethernet traffic classes without interference.
TTEthernet device implementation expands standard Ethernet with services to meet time-critical, deterministic or safety-relevant requirements in double- and triple-redundant configurations for advanced integrated systems. TTEthernet switching devices are used for integrated systems and safety-related applications primarily in the aerospace, industrial controls and automotive applications.
TTEthernet has been selected by NASA and ESA as the technology for communications between the Orion MPCV (Multi-Purpose Crew Vehicle) and the European Service Module (ESM), and is described by ESA as being "prime choice for future launchers allowing them to deploy distributed modular avionics concepts" 2) 3)
NASA's Orion Multi-Purpose Crew Vehicle (MPCV) is the successor to the famous Space Shuttle. As a next generation spacecraft it will enable humanity to explore space beyond low earth orbit for the first time in over 40 years, including distant asteroids, the moons of Mars or Jupiter and other places in our solar system, marking the beginning of a new era in space exploration. 4)
TTEthernet is the spacecraft's "nervous system"
One of Orion's most important systems is the avionics system, often described as the "brains" of the spacecraft. The avionics system consists of a wide variety of standard and complex electronics assembled into various independent systems, each responsible for performing specific critical functions. TTEthernet is at the core of this "nervous system" allowing a mixed criticality architecture using all three traffic classes of TTEthernet, i.e. standard, rate-constrained and time-triggered Ethernet, thus being highly flexible and modular. All independent avionics sub-systems of MPCV were connected by using this deterministic high performance Ethernet network.
Benefits of TTEthernet® for space applications: 5)
• Modular and scalable system architectures enable cost savings
• Use of a single network for command and control as well as payload data simplifies spacecraft avionic
• Up to 1 Gbit/s bandwidth supports applications demanding high-speed and large amounts of data
• Time synchronization implemented in hardware saves costs for dedicated software and network integration
• Precise time distribution via the network (to any subscriber) enables building of safety-critical systems
• Deterministic data transfers characterized by predictable jitter and guaranteed transmission latency to realize real-time functions
• Fault tolerance and fault containment in hardware to increase safety and keep the system operational at all times
• Interoperability with standard Ethernet provides more flexibility in applications.
TTTech Aerospace of Vienna, Austria, provides deterministic embedded network and platform solutions for aerospace applications. For the space sector, it offers reliable radiation-hardened components and integrated modules for Deterministic Ethernet networking applications designed for the use in extreme environmental conditions found in space exploration and human-rated space flight missions.
TTTech Aerospace's avionic backbone network systems act as the "central nervous system" of e.g. NASA‘s Orion Multi-Purpose Crew Vehicle (MPCV), the European Service Module by ESA (ESM) and the Ariane 6 launch vehicle. The International Deep Space Interoperability Standards agreed on by NASA, ESA, JAXA and CSA establish TTEthernet®, the network technology developed by TTTech, as the core standard interface of the "International Avionics Systems Interoperability Standards (IASIS)" for future deep space applications, which include the Gateway.
TTTech Aerospace is part of TTTech Computertechnik AG, a technology leader in safety control platforms and real-time networks. TTTech Computertechnik AG operates under the umbrella of the TTTech Group, a globally oriented group of high-tech companies head-quartered in Vienna, Austria. The TTTech Group builds on 20 years of technology leadership with extensive experience in collaborating with market leaders in the automotive, off-highway, industrial and aerospace industries.
About TTEthernet: TTEthernet is a highly deterministic version of Ethernet and is fully compatible with the standard IEEE Ethernet networks found in every home and office around the world. On board of the Orion, TTEthernet helps to connect almost 50 communication endpoints and moves data at a rate 1,000 times faster than the old systems of the Space Shuttle. As a single network it supports all of Orion's data transfers and communication with less mass, power and cost than the old multisystem network approach. These savings are achieved because it is now possible for the first time to robustly integrate highly critical real-time functions like flight controls and life-support systems with lower priority data on one single physical network while guaranteeing predictable system behavior.
TTTech Technology from Outer Space for Everyday Use: Apart from the Orion spacecraft, TTEthernet is used in many other applications across various industries: It enables autonomous docking maneuvers in space but is also used in automotive applications. TTEthernet will further facilitate new advanced functions on board of helicopters as well as civil and military aircraft. 6) 7)
1) "TTEthernet," Wikipedia, URL: https://en.wikipedia.org/wiki/TTEthernet
2) "Time-Triggered Ethernet," ESA Enabling & Support, URL: https://www.esa.int/Enabling_Support/Space_Engineering_Technology
3) "TTEthernet – A Powerful Network Solution for All Purposes," TTTech, 2014, URL: https://web.archive.org/web/20140328151014/http://www.tttech.com
4) "NASA's Orion Multi-Purpose Crew Vehicle (MPCV)," URL: https://www.tttech.com/markets/market-overview/space/projects-references/nasa-orion/
5) "Exploring New Ways to Simplify Spacecraft Software and System Architectures," TTTech, URL: https://www.tttech.com/wp-content/uploads/TTTech_Aerospace-Space-Core-Brochure.pdf
6) "Scalable, high-speed avionics for safety-critical space applications," Space Daily, 3 January 2022, URL: https://www.spacedaily.com/reports/Scalable_high_speed
7) EleftheriosKyriakakis, MajaLund, LucaPezzarossa, JensSparsø, MartinSchoeberl, "A time-predictable open-source TTEthernet end-system," Journal of Systems Architecture, , Volume 108, Published: September 2020, 101744, https://doi.org/10.1016/j.sysarc.2020.101744, URL: https://tinyurl.com/2p96t6bz
The information compiled and edited in this article was provided by Herbert J. Kramer from his documentation of: "Observation of the Earth and Its Environment: Survey of Missions and Sensors" (Springer Verlag) as well as many other sources after the publication of the 4th edition in 2002. - Comments and corrections to this article are always welcome for further updates (email@example.com).