What is Automotive Ethernet?
Automotive Ethernet is a variant of the Ethernet protocol that has been specially developed for vehicles. Ethernet is a widespread protocol which operates at the physical layer of the ISO/OSI layer model and is used in static applications such as buildings and company networks. Automotive Multi-Gigabit Ethernet is a variant specially developed for vehicles, which supports data transfer rates of between 2.5 and 10 gigabits per second, and is defined in the IEEE 802.3ch-2020 standard.
Development of Automotive Multi Gigabit Ethernet
Due to modern driver assistance systems, the quantity of data to be processed in vehicles has been continuously increasing for years. The short reaction times of these systems is guaranteed by the recording of extensive information about the vehicle’s environment by sensors and cameras. The more data collected about the current road traffic situation, the earlier the systems can detect dangers and prevent dangerous situations from occurring. High-speed transmission standards are required for data to be transmitted to a control unit. Currently, we are talking about hundreds of Mbit/s or even Gbit/s. The tried and tested transmission technologies from the automotive industry such as CAN, MOST or FlexRay are no longer able to meet these high demands. Over the years, countless extremely high-performance, proprietary solutions have emerged such as APIX or GMSL, also known as SerDes (or Serializer/Deserializer) technologies. As an alternative to these purely automotive developments, the idea was born to develop protocols from general network technology in order to meet the particular requirements of vehicles, and this was how Automotive Ethernet emerged.
Differences between Automotive Ethernet and conventional Ethernet
The “normal” Ethernet standard with a data rate of 10 Gbit/s (IEEE 802.3ae-2002) was defined back in 2002, and was prescribed for fiber-optic connections. The 10 Gbit/s Ethernet standards for common copper cables appeared in 2004 in the form of “IEEE 802.3ak” for twin axial copper cables, and in 2006, in the form of “IEEE 802.3an” for twisted pair cables. The standard for twisted pair cables is known as “10GBASE-T” and prescribes transmission via four twisted-pair cables in exactly the same way as with the predecessor standard 1000BASE-T (1 Gbit/s). The data rate of maximum 10 Gbit/s is divided between all four pairs, each with 2.5 Gbit/s. In the process, the data rate is achieved in full duplex mode. This means that 10 Gbit/s are transmitted in both directions of the communication line at the same time. However, for the application in vehicles, stricter requirements apply than for installation in buildings. The cables used must be lightweight, cheap, mechanically resistant, and ensure high functional security. In addition, communication in the vehicle must be absolutely reliable and ideally should take place in real time. In its original form, Ethernet is not suitable for these requirements. So this is why Automotive Ethernet was developed. To start with, when the 100 Mbit/s variant “100BASE-T1” emerged from BroadR-Reach (Broadcom’s proprietary standard), “1000BASE-T1”, a 1 Gbit/s variant, and eventually also “10GBASE-T1”, a multi-gigabit version (IEEE 802.3ch-2020) also appeared. In order to achieve lower data rates such as 2.5 Gbit/s and 5 Gbit/s, what are known as “scaling parameters” were implemented in the 10GBASE-T1 standard, with which the data rates can be regulated from the top downwards. For speeds of 2.5 Gbit/s, 5 Gbit/s and 10 Gbit/s, these same requirements apply to the transmission path components. Automotive Ethernet uses just one twisted pair of wires which can be recognized by the abbreviation “-T1”. This is possible, among other things, because the link lengths in vehicles are significantly shorter than those in building networks. The commonly used 8P8C connectors from network technology are not suitable for use in vehicles due to the number of contacts and the requirements for mechanical stability. Special connectors are used which are optimized for use in vehicles in terms of their robustness, performance and costs. As an alternative to electrical transmission, in 2023, the Automotive Multi-Gigabit Ethernet standard “IEEE 802.3cz-2023” was published for the transmission of 2.5 Gbit/s to 50 Gbit/s via fiber optic conductors.
Application areas of Automotive Ethernet
The onboard architecture is increasingly developing from a domain-based to a zone-based architecture with zone controllers. In the past, control units were developed according to their specific tasks and distributed around the vehicle which led to complex cable harnesses with, in some cases, over 100 control devices. Modern SoCs enable the bundling of sensor data in vehicles zones which are managed by high-performance zone controllers. This reduces the number and length of the cables, which decreases both weight and production costs.
The connection between the central computer and the zone controllers is identified as the backbone connection, which requires high bandwidths. Current SerDes solutions achieve similar data rates such as Automotive Ethernet, but, due to their asymmetrical transmission, are optimized for applications such as displays and cameras. Therefore, Automotive Multi-Gigabit Ethernet, which enables full duplex transmission, is a suitable technology for these backbone connections in modern vehicles.
Jonas Rumold
Jonas Rumold is a Junior Development Engineer in high-frequency development at MD ELEKTRONIK. His responsibilities include high-frequency measuring devices, measurement methods, evaluation of shielded and unshielded high-frequency data cables, and the current standards for data transmission in the automotive sector.