Automotive Ethernet
Traditional vehicular networks, such as CAN, have limitations in bandwidth and were not originally designed for the high-speed data transfer requirements of modern cars. As higher bandwidth was required for ADAS and OTA update distribution, new solutions were needed. Standard 100BASE-TX Ethernet was considered, but was not designed for the strict EMC requirements of automotive applications.
Together with Broadcom, BMW customized Broadcom's BroadR-Reach standard to meet the requirements of automotive applications. This standard was later standardized by the IEEE as 100BASE-T1 or 802.3bw. As a proof of concept, BMW used it to distribute camera streams for the surround view in their 7 Series cars.
In 2020, the IEEE standardized 10BASE-T1S or 802.3cg, which is a low-speed version of 100BASE-T1. This standard is intended to replace traditional low-speed networks such as LIN and CAN. Unlike the higher-speed variants, it supports multidrop, meaning no hubs or switches are needed and multiple ECUs can be connected to the same bus.
History
- 2011 — Formation of the OPEN Alliance.
- 2016 — Standardization of IEEE 802.3bw-2015 (100BASE-T1, BroadR-Reach).
- 2016 — Standardization of IEEE 802.3bp-2016 (1000BASE-T1).
- 2020 — Standardization of IEEE 802.3cg-2019 (10BASE-T1S).
Overview of IEEE Standards
The term Automotive Ethernet encompasses a wide variety of standards on the physical layer that range from 10 Mbit/s all the way up to 10 Gbit/s. They all use Ethernet MAC, while higher-layer protocols such as TCP/IP and UDP/IP depend on the application. Development is driven by the OPEN (One Pair Ether-Net) SIG.
| Name | IEEE Standard | Year Published | Speed |
|---|---|---|---|
| 100BASE-T1 | 802.3bw | 2016 | 100 Mbit/s |
| 1000BASE-T1 | 802.3bp | 2016 | 1 000 Mbit/s |
| 10BASE-T1S | 802.3cg | 2020 | 10 Mbit/s |
| 2.5GBASE-T1 | 802.3ch | 2020 | 2 500 Mbit/s |
| 5GBASE-T1 | 802.3ch | 2020 | 5 000 Mbit/s |
| 10GBASE-T1 | 802.3ch | 2020 | 10 000 Mbit/s |
100BASE-T1 / BroadR-Reach
The first use of automotive Ethernet was 100BASE-T1, which was originally developed as BroadR-Reach by Broadcom. It's a full-duplex point-to-point connection over a single unshielded twisted pair. It can reach speeds up to 100 Mbit/s. In 2016, it was standardized as IEEE 802.3bw-2015.
By using an efficient three-level pulse amplitude modulation scheme (PAM3) it only needs a bandwidth of about 33.3 MHz, which is about half of traditional 100BASE-TX Ethernet. This modulation scheme also allows for more aggressive EMC filtering. These properties reduce EMI and make 100BASE-T1 suitable for automotive applications.
1000BASE-T1
1000BASE-T1 is an extension of 100BASE-T1 to allow for higher speeds. It allows up to 1 Gbit/s of full-duplex bandwidth over a single twisted pair, still using unshielded cables. It was standardized as IEEE 802.3bp-2016.
1000BASE-T1 uses the same PAM3 encoding scheme as 100BASE-T1, but with a 750 MHz symbol rate.
10BASE-T1S
In 2020, 10BASE-T1S was standardized as IEEE Std 802.3cg-2019 as a possible replacement for traditional low-speed and low-cost networks such as CAN. This means Ethernet can be used throughout the entire car, from low-speed networks to high-speed networks.
Unlike other variants of Automotive Ethernet, it supports multidrop, allowing connection of multiple ECUs on the same bus without needing any gateways. To prevent collisions, it uses a coordinator node to choreograph transmit opportunities for all nodes on the network in a system called PLCA (Physical Layer Collision Avoidance). Each node gets assigned a transmit opportunity in a round-robin fashion. The slots do not have a fixed length, so very little time is wasted when a node has no data to send compared to TDMA schemes used in FlexRay or TT-CAN.
It has a maximum speed of 10 Mbit/s and uses a single twisted pair. When used in a point-to-point connection it supports full-duplex. When used in a multidrop configuration it uses half-duplex.