AUTOMOTIVE ETHERNET

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WHAT IS ETHERNET?

First developed in 1973, Ethernet has displaced virtually all competing technologies due to its simplicity and scalability. The popular Ethernet versions range in speed from 10 Mbps all the way up to 400 Gbps, with different media, ranging from coaxial cable over twisted pair cables to fiber optic transmission. Due to the huge volumes deployed, the hardware cost for the most widely used Ethernet interfaces with 100 Mbps (Fast Ethernet) and 1 Gbps (Gigabit Ethernet) have become very low.

Layer Preamble Start frame delimiter (SFD) MAC destination MAC source 802.1Q tag (optional) Ethertype (Ethernet II) or length (IEEE 802.3) Payload Frame check sequence (32-bit CRC) Interpacket gap
7 bytes 1 bytes 6 bytes 6 bytes (4 bytes) 2 bytes 46-1500 bytes 4 bytes 12 bytes
Layer 2 Ethernet frame ← 64–1522 bytes →
Layer 1 Ethernet packet & IPG ← 72–1530 bytes → ← 12 bytes →

The standardized Ethernet frame format according to IEEE 802.3

WHAT IS AUTOMOTIVE ETHERNET?

Automotive Ethernet is a range of new Ethernet versions that have been standardized to meet the specific requirements of automotive communication. These new Automotive Ethernet versions feature technologies for higher robustness in the automotive environment while allowing significant cost reductions.

A large amount of development effort has gone into ECUs with legacy technologies. Therefore, the automotive industry is not switching to an Ethernet-only scenario without intermediate steps. Instead, some established non-Ethernet ECUs will continue to be used, creating mixed Ethernet / legacy deployments. Therefore, for some time there will be a need to support both legacy protocols as well as legacy technologies.

Complementing the transition to Automotive Ethernet, E/E Architecture is transitioning to a Zonal based Architecture. This transition increases the need for low latency routing decisions (to accommodate multi-hop routing) while still supporting the increasing multi-gigabit traffic through the ring backbone. Current vehicle mechanisms, like Zonal Gateways, are becoming communication bottlenecks. Therefore HW based routers are essential to provide ultra-low latency, cost-effective design with an ever-increasing amount of interfaces and traffic requirements.

CAN Bus vs. Automotive Ethernet

In comparison to CAN, Automotive Ethernet offers a strong solution to the issues caused by the traditional CAN bus architecture. Cars need a high-performance backbone that can support the increased communication from vehicle’s new software to create the driver-centric experience. Trends are showing carmakers moving away from the more traditional complex wiring to a Zonal Architecture that relies on an Ethernet backbone to run smoothly and securely.

  • Support for significantly higher throughput rates (in excess of 10Gbps), allowing aggregation of multiple CAN buses into a single Ethernet link. This results in smaller wiring harnesses than CAN which translates into lower installation and maintenance costs
  • Support of quality of service and time-sensitive networking (TSN), allowing real-time communication to be multiplexed with lower priority data
  • Advanced security features and transport layer services
  • Plug and play capabilities so components can be connected and disconnected as needed with automatic detection and configuration

There is also a downside to transitioning to Ethernet which includes a more costly controller and physical-layer interface, complicated electromagnetic compatibility issues, as well as overhead for allowing for real-time communication (e.g. TSN). But it doesn’t seem that the bad outweighs the good in the question of automotive Ethernet vs. CAN.

Ethernet’s flexibility over a vehicle’s lifecycle is what gives it the edge as more and more lines of code are added to car models to support the multitude of infotainment, safety, personalization, and autonomous driving features along with over-the-air updates.

It’s important to note that Ethernet will not replace all legacy connectivity like CAN, CAN-FD, LIN or FlexRay, and we will continue to see a mix of different communication protocols and methods for many years.

Requirements for communication in automotive environments

Control and communication mechanisms within a vehicle are very diverse in terms of requirements for bitrates, latency, reliability, and security. The mechanism used must be able to provide the needed requirements for different kinds of function. Ranging from relatively minor performance demands to more demanding applications and services:

  • A comparatively simple ECU like the windshield wipers or seat ECUs. These devices have lower-speed requirements in the order of kilobits per second and aren’t highly sensitive in terms of latency, security, and reliability.
  • An ECU for connecting an external camera or sensor. This requires enough computing power to compress the data or raw video stream down to several megabits per second, at most. While security and reliability requirements are moderate, latency requirements are strict as the video stream is watched in real time.
  • Critical safety functions, like ABS or power steering where latency, security and reliability requirements are extremely high. Any unauthorized use of these functions has to be avoided, and the actors have to enter into a fail-safe mode in the case of failure.
  • Maintenance like firmware updates of ECUs. This adds requirements in terms of higher bitrates in order to make the update reasonably fast as well as in terms of security to ensure that malware does not find its way into ECUs. While this is already an issue for regular ‘hands on’ maintenance at the dealership, it becomes very critical for Over-the-Air (OTA) updates where the external communication channels could be compromised.
  • Security. This has to be a system-wide consideration that must include inter-ECU communication, external communication, and all the processes running on the ECUs, with particular focus on software update processes.

Legacy automotive communication mechanisms

The need to interconnect various ECUs within a vehicle was recognized in the 1980s. Vehicle manufacturers started with proprietary solutions as ECU interconnectivity was thought to be a differentiating feature and there was a lack of available standards in the industry. While these solutions were introduced in series production later on in the early 1990s, the high cost, driven by low component volume, and general lack of interest by customers, led to joint standardization activities across the entire vehicle industry, enabling common cost effective solutions with high volumes of components. This yielded an additional benefit of grabbing the attention of semiconductor and other component vendors.

Controller Area Network (CAN)
Local Interconnect Network (LIN)
Media Oriented Systems Transport (MOST)
Flexray
Controller Area Network (CAN)

CAN has become the most widely deployed internal communication network technology in vehicles. CAN represents a bus system with differential transmission although more complex topologies involving stubs can also be implemented. It provides speeds from 125 kbps to 5 Mbps.

Local Interconnect Network (LIN)

LIN is a lower cost alternative for simple applications like power windows, rain sensors, or central locking. LIN uses a single-wire transmission, a maximum data rate of 19.2 kbps and up to 16 ECUs on a single bus.

Media Oriented Systems Transport (MOST)

As the requirements for vehicle infotainment increased with the advent of navigation systems, driver support systems, and elaborate comfort functions, MOST was introduced as the mechanisms to integrate all these features reliably and securely while also supporting the needed bitrates.

Flexray

Safety critical functions like steering, braking, and airbags require a highly reliable and secure communication mechanism with strict timing capabilities. FlexRay defines the Physical (PHY) and Data Link Layer (DLL). The gross data rate in FlexRay is 10 Mbps and uses differential transmission across UTP. However, the number of ECUs in a single branch is typically limited to 4 or 5.

"The name Ethernet refers to the historical perception of the ether as the medium in which electromagnetic waves propagate."

Automotive Ethernet

Everything is Software (Almost)

Automotive Ethernet has solved the requirements for ever increasing throughput and bitrates and low latency and flexibility stemming from increasingly complex and bitrate-hungry internal and external communications.

In today’s vehicles, each legacy technology uses its own packet format, speed, media, access mechanisms, and protocols. Some ECUs have to support multiple different technologies on their ports, adding complexity and cost as the volumes for components are split across multiple technologies.

In contrast, Ethernet has proven extremely flexible, scaling across a range from 10 Mbps all the way up to 400 Gbps leaving everything unchanged except the physical layer and the speed requirements of the implementation. This allows seamless layer 2 networking using bridges between network segments even with different Ethernet versions. Switches / bridges typically have autosensing / auto-negotiating ports which can adapt to the speed classes of the systems connected to them. So there is no need for any protocol conversion when an installation uses multiple different variants concurrently. That being said, the transition to an Ethernet-only scenario will take time and until its completion, both legacy protocols and technologies will need to be supported.

ZONAL ARCHITECTURE

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Automotive Ethernet technologies

Ethernet alone is not suitable for automotive, so introducing Ethernet in an automotive environment poses a number of unique challenges especially related to the physical layer.

Compared to other industries, the automotive environment has particular challenges in terms of cost and environmental conditions – like temperature, mechanical stress, electromagnetic compatibility (EMC), and reach. To meet these challenges, a family of new Ethernet versions has been standardized covering the entire range of speeds relevant to automotive communication. These versions represent strongly simplified and robust technologies, and they have, in turn, been introduced into other industries where the robustness and / or the cost position of these technologies provides an advantage.

  • 100BASE-T1 - uses single unshielded twisted pair cables with a maximum length of 15 meters. The bridge, composed of 4 resistors, separates, transmits, and receives directions on each side of the link.
  • 1000BASE-T1 - with the emergence of connected and autonomous vehicles and more sophisticated infotainment systems, the information exchanged within a vehicle has grown rapidly. 100BASE-T1 has been introduced as the definition of a Gigabit Ethernet technology for automotive use.
  • 1000BASE-RH - uses Polymeric Optical Fiber (POF). POF is immune to any EMC problem, and it also provides galvanic isolation.
  • 10BASE-T1S - a low-speed, low-cost Ethernet solution for I applications that only need very low bitrates for communication.
  • MultiGBASE-T1 - a set of new PHYs with 2.5, 5 and 10 Gbps supported over Shielded Twisted Single Pairs (STSP) to support high bitrate and external communication for AI evaluation.

PoDL

The wiring harness is a significant cost and weight factor in vehicles. Being able to cut down the number of wires in the harness will reduce costs and more importantly, reduce weight. Therefore, it is highly advantageous to be able to use data cables to supply power to ECUs without a separate power supply network.

In Ethernet versions for office or home use, Power over Ethernet (PoE) has been available for many years, providing power to devices like wireless access points or IP phones, where the provision of dedicated power supplies would be inconvenient if not impossible.

Using power over the automotive Ethernet versions with twisted single pair cables is comparatively straightforward. PoDL has been standardized by IEEE as 802.3bu.

MACsec

MACsec is a security standard defined by IEEE as 802.1AE. It operates at the medium access control layer and defines connectionless data confidentiality and integrity for media access independent protocols. The MACsec frame format is similar to the Ethernet frame format. It includes a security tag which is an extension of the EtherType and a Message Identification Code which is used to authenticate a message.

Audio Video Bridging (AVB)

AVB and TSN are the two key IEEE standards to enable reliable real-time data transfer for Automotive Ethernet applications. This type of Ethernet gives engineers the tools to design automotive networks with predictable latency and guaranteed bandwidth. TSN hardware support enables robust, low-latency and deterministic synchronized packet transmission to meet the ISO 26262 requirements of safety-critical control systems like braking or steering.

Diagnostics Over Internet Protocol (DoIP)

Diagnostics over IP enables much higher data rates than CAN, creating large potential savings both in terms of time and expenses when complex diagnostic tasks and flash applications are needed. Ethernet-based communication allows new concepts in vehicle diagnostics, for example direct vehicle access from the tester, and considerably simplified integration of the diagnostic interface into the IT infrastructure.

Higher layer Protocols

With the adoption of Ethernet the automotive industry has also embraced IP for the Network Layer and TCP and UDP for the transport layer, as well as some other standard protocols. Below is a chart providing the Protocol overview for Automotive Ethernet.

Audio / video transport Time sync Automotive NM Diagnosis and flashing Control comm. Service discovery Address config. Address resolution, signaling, etc.
IEEE 1722 (AVB) IEEE 802.1AS (AVB) UDP-NM DoIP SOME / IP SOME / IP-SD DHCP ICMP ARP
UDP TCP and / or UDP UDP
IP
Ethernet MAC / IEEE DLL, 802.1Qx, VLANs
Ethernet PHY

What’s next for Automotive Ethernet?

The communication requirements inside vehicles and towards the external world have changed dramatically.

Inside, the number of ECUs and the complexity of their interconnection has become unmanageable. The requirements with respect to capacity and security can no longer be met by the legacy technologies alone that have been used for many decades. Connected and autonomous driving is intensifying this change.

Customers demand functionality and quality of the infotainment systems similar to what they know from their home entertainment systems and smartphones.

External communication between the vehicle and the environment is growing and has multiple facets:

  • V2X as the communication with the vehicle’s environment for safety purposes, remote maintenance like over the air upgrades, and preventive maintenance activities
  • Human communication like phone and video calls and messaging

The internal safety-critical communication has to be protected strictly against attacks reaching the vehicle through external wireless networks.

The sum of all these requirements can only be met by a redesigned communications infrastructure based on a consistent scalable technology that is able to support all communication needs from low-speed controller interaction up to uncompressed video transfer for safety functions in autonomous vehicles, with multiple gigabits per second.

The automotive industry has joined other industries that have already moved to Ethernet as standard communication mechanism before. Ethernet can provide the needed range of bitrates from 10 Mbps all the way up to hundreds of gigabits per second, providing low latencies as required for real-time communication, and enabling cost-adapted solutions for the different application scenarios, like low-cost low-bitrate communication to feed simple controllers, up to high-speed sophisticated attachments of high-resolution cameras.

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