Comprehensive analysis of automotive Ethernet technology and its standardization

With the increasing complexity, networking and broadband of automotive electronics, automotive Ethernet has a broad development space in the car in line with this development trend. This paper provides a comprehensive analysis and introduction of the vehicle Ethernet technology, including its origin, definition, development trend, main technology and its standardization.

1 Introduction

Ethernet, a local area network (LAN) technology since its invention in 1973, has experienced more than 40 years of development and has become the most widely used LAN technology. Ethernet is mainly standardized by the IEEE 802.3 working group. Ethernet starts from the initial support of 10Mbit/s throughput, and has been continuously developed to support Fast Ethernet (100Mbit/s), Gigabit Ethernet (1Gbit/s), and 10,000. Mega Ethernet (10Gbit/s) and 100Gbit/s. At the same time, in order to adapt to the diversification of applications, the Ethernet rate broke the convention of upgrading by 10 times, and began to support the rates of 2.5, 5, 25 and 400 Gbit/s. Ethernet technology supports not only twisted-pair copper wire transmission media, but also fiber-optic transmission. As the Metro Ethernet Forum (MEF) continues to use Ethernet technology as a switching technology and transmission technology for metropolitan area network construction, Ethernet is not only limited to LAN applications, but can be more widely applied to metropolitan area networks (MAN). ) and the field of wide area networks (WANs).

Before entering the automotive field, Ethernet has gained wide application, while also having the advantages of mature technology, high standardization, high bandwidth and low cost. With the rapid development of automotive electronics in recent years, the number of electronic products in the car has increased year by year, and the complexity has been increasing. The technological advantages of Ethernet are well suited to the needs of car manufacturers for in-car internet. However, due to the strict requirements of electromagnetic compatibility in the car, Ethernet has not achieved technical breakthroughs in recent years and has been applied to automobiles.

At present, the technical standard of mainstream car Ethernet is based on Broadcom's BroadR-Reach (BRR) technology. The IEEE has completed standardization of 100Mbit/s car Ethernet technology and is standardizing on car Ethernet with 1Gbit/s transmission speed. . In-vehicle Ethernet will be mainly used in systems with high bandwidth requirements (see Figure 1), such as Advanced Driver Assistance Systems (ADAS), On-Board Diagnostic Systems (OBD), and in-vehicle infotainment systems. Unlike traditional in-vehicle networks, in-vehicle Ethernet can provide the higher data transmission capabilities required for bandwidth-intensive applications, and it will have broad application prospects in the future.

2. Car Ethernet technology

2.1 What is car Ethernet?

Car Ethernet is a new LAN technology that uses Ethernet to connect in-car electronic units. Unlike ordinary Ethernet using 4 pairs of unshielded twisted pair (UTP) cables, car Ethernet can achieve 100Mbit/s or even 1Gbit/s data transmission rate on a single pair of unshielded twisted pair cables, and should also satisfy the car. Industry requirements for high reliability, low electromagnetic emissions, low power consumption, bandwidth allocation, low latency, and simultaneous real-time performance.

The physical layer of the car Ethernet uses Broadcom's BroadR-Reach technology. The physical layer (PHY) technology of BroadR-Reach has been standardized by the One-pair Ethernet Alliance (OPEN), so it is sometimes called the car ether. The network is BroadR-Reach (BRR) or OABR (Open Alliance BroadR-Reach).

The MAC layer of the car Ethernet uses the IEEE 802.3 interface standard to seamlessly support widely used high-level network protocols (such as TCP/IP) without any adaptation.

2.2 Car Ethernet main technology

The technical architecture of the car Ethernet and the upper layer protocols supported by it is shown in Figure 2. Car Ethernet mainly involves the 1 and 2 layers of OSI technology. This article introduces the main technologies of car Ethernet.

(1) Physical layer PHY

Automotive Ethernet uses a single pair of unshielded cables and a smaller, compact connector that supports 15m of transmission distance when unshielded twisted pair cable is used (40m for shielded twisted pair). This optimized processing enables on-board Ethernet Meet the automotive EMC requirements. The 100M Car Ethernet PHY uses 1G Ethernet technology to achieve two-way communication on a single pair by using echo cancellation. The main differences between the physical layer of the car Ethernet and the physical layer of the standard 100BASE-TX are:

● Compared with the scrambler used in 100BASE-TX, the car Ethernet digital signal processor (DSP) uses a highly optimized scrambler to better separate signals, which is more efficient than the 100BASE-TX system. .

● The signal bandwidth of the car Ethernet is 66.7MHz, which is only half of the 100BASE-TX system. The lower signal bandwidth improves return loss, reduces crosstalk, and ensures that the vehicle Ethernet meets automotive electromagnetic radiation standards.

(2) "One pair of data lines power supply" PoDL

Power over Ethernet PoE technology was introduced in 2003 to provide 15.4W of power through a standard Ethernet cable. Supporting both power and data transmission on a single cable makes sense to further reduce the weight and cost of the cable on the car. Since the conventional PoE is designed for 4-pair cable Ethernet, PoDL has been developed specifically for in-vehicle Ethernet to provide a 12VDC or 5VDC supply voltage for the normal operation of the electronic control unit ECU on a pair of cables.

(3) Advanced Cable Diagnostics ACD

The ACD function can detect the fault location of the cable by analyzing the amplitude and delay of the reflected signal, which is critical to achieving a high level of reliability for the in-vehicle Ethernet connection.

(4) Energy efficient Ethernet

When the engine is turned off, the electronic units on the car are not all turned off. At this time, the battery needs to be powered, and the battery power is limited. In this case, high-performance Ethernet technology can be used to reduce the consumption by shutting down the unused network. Electricity.

(5) Time synchronization

Some applications in the car need to achieve time synchronization between different sensors, or need to know the time of different nodes when performing a certain measurement, which requires synchronization between all the nodes participating in the test, and some precision even needs to reach Microsecond level. The car Ethernet uses the IEEE 802.1AS timing synchronization standard, which uses the IEEE 1588V2 profile to determine the master clock in a simpler and faster way, specifying the generalized precision time protocol (gPTP).

(6) Time-triggered Ethernet

Many controls within the car require communication delays in the microsecond range. In traditional Ethernet, new packets are processed only when existing packets are processed, even at Gbit/s rates, which require hundreds of microseconds of delay, which does not meet the needs of in-vehicle applications. To address this issue, the IEEE 802.3 Working Group developed a high-priority fast packet technology that allows fast packets to be inserted into the queue of packets being processed to be prioritized to ensure that the delay is in the microsecond range.

(7) Audio and video bridge AVB

In order to meet the low latency and guaranteed bandwidth requirements of in-car audio and video applications, AVB related standards developed by the IEEE 802 working group can be used in the car.

AVB technology provides core functions such as priority, flow reservation protocol (SRP), and traffic shaping protocol (FQTSS). AVB's applications in the car include lip-sync multimedia playback, online navigation maps and other automotive networking applications, ADAS and diagnostic functions.

The IEEE also developed the AVB transport protocol, including:

IEEE 1722-2011: A time-sensitive application in the bridged LAN. Layer 2 transport protocol standard, also known as Audio Video Transport Protocol (AVTP).

IEEE 1733-2011: Layer 3 transport protocol standard for time-sensitive applications in bridged LANs. Since the agreement is a third-tier agreement, it is not expected to be widely adopted by the automotive industry.

In order to improve the adaptability of AVB and meet more application scenarios such as industry, the IEEE AVB task group has been renamed as the "Time Sensitive Network" TSN Working Group. Now it is one of the five major task groups of IEEE802.1, dedicated to the development of ultra low time. Extended control network.

2.3 Car Ethernet Development Trend

In-vehicle electronics have become increasingly complex, and more and more sensors, controllers, and interfaces are increasingly demanding bandwidth, and the need for different computing units and different domains to communicate with each other is growing. This complexity directly led to an increase in the use of in-vehicle connections. Before the automotive Ethernet enters automotive applications, there are many different standard technologies in use, including LIN, CAN, FlexRay, MOST, and LVDS. Almost every automotive electronic device has its own specific cable and communication requirements, which inevitably leads to complex wiring in the car. The wiring harness inside the car has become the third largest cost in the car outside the engine and chassis. The labor cost of wiring in the middle accounts for 50% of the whole vehicle. At the same time, the wiring harness inside the car is also the third part of the weight except the chassis and the engine. The technology to reduce the weight of the harness will directly improve the economics of fuel use. On-board Ethernet is carried on a single-pair, unshielded twisted-pair transmission medium. Using smaller and more compact connectors, it can reduce up to 80% in-vehicle connection costs and up to 30% in-vehicle wiring weight.

According to Frost & Sullivan and Strategy Analysis, the world's leading consulting firms, 400 million in-vehicle Ethernet ports will be deployed worldwide by 2020; by 2022, all car Ethernet will be deployed globally by 2022. The port will exceed the sum of all other deployed Ethernet ports. Frost & Sullivan also predicts that by 2020, there will be 6 to 40 car Ethernet nodes per vehicle for low-end models, and 50 to 80 car Ethernet nodes for luxury and hybrid/electric models. On-board Ethernet is used in 40% of sold cars; by 2025, the market penetration of automotive Ethernet will increase to 80%.

As of the end of March 2016, the number of OPEN members in the automotive Ethernet field has grown to 300, including many automakers, Tier 1 suppliers, chip vendors, technology companies and research institutions in the automotive sector. Chinese car companies and suppliers are also actively paying attention to and gradually adopting the technology of OPEN Alliance. In the OPEN alliance, there are more than a dozen such as FAW Group, Beiqi, Great Wall, Pan Asia, Brilliance, Hengrun, Hangsheng and China Institute of Information and Communication. Chinese member. The number of mainstream automakers using OABR technology is growing worldwide. By the end of October 2015, there have been a number of models using in-vehicle Ethernet, including BMW's X3, X4, X5, X6, i3, i8, 6 Series and 7 Series, Jaguar XJ and XF, and Volkswagen Passat.

3. Car Ethernet standardization

In the standardization of automotive Ethernet, the following four standardization organizations or alliances have played a major role in promoting the IEEE 802.3 and IEEE 802.1 working groups, the Automotive Open Systems Architecture Alliance AUTOSAR, the OPEN Alliance, and the AVnu Alliance. image 3.

3.1 IEEE

The LAN standard developed by IEEE 802.3 represents the mainstream Ethernet technology in the industry. The vehicle Ethernet technology is developed on the basis of IEEE802.3. Therefore, IEEE is the most important international standardization mechanism for automotive Ethernet. In order to meet the requirements of the car, it involves the development of several new specifications in the IEEE 802.3 and 802.1 working groups and the revision of the original specifications, including the PHY specification, the AVB specification, and the single-line data line power supply.

In addition, specifications such as AV transmission and timing synchronization in AVB are also required to be standardized by other IEEE technical committees, such as IEEE 1722 and IEEE 1588.

3.2 OPEN

The OPEN Alliance was founded in November 2011 by Broadcom, NXP and BMW to promote the adoption of Ethernet-based technology standards for in-vehicle networking. The relevant unit may become a member of the OPEN Alliance's Code of Acceptance Agreement and participate in the development of its relevant norms.

The main standardization objectives of OPEN are:

● Develop a physical layer standard of 100 Mbit/s BroadR-R and promote it as an open industry standard.

• Encourage and support the development of higher speed physical layer specifications in relevant standardization organizations.

● Develop interoperability requirements for OPEN and select third parties to perform interoperability testing.

● Discover the standardization gap in the implementation of automotive Ethernet.

The OPEN Alliance forms a close standardization cooperation with IEEE802.

3.3 AUTOSAR

AUTOSAR is an alliance of car manufacturers, suppliers and tool developers to develop an open, standardized automotive software architecture. The AUTOSAR specification includes the vehicle TCP/UDP/IP protocol stack. AUTOSAR has gained widespread acceptance in the automotive industry, and manufacturers will abandon the development of private standards and compete on standards implementation. The AUTOSAR standard enables multiple devices to run seamlessly on the same shared network.

3.4 AVnu

The AVnu Alliance was established by Broadcom in conjunction with Cisco, Harman and Intel to promote the IEEE 802.1 AVB standard and Time Synchronous Network (TSN) standards, establish authentication systems, and address such things as precise timing, real-time synchronization, bandwidth reservation, and traffic shaping. And other important technical and performance issues.

Currently, AVnu has released its certification specification for automotive Ethernet AVB and has certified multiple models.

It should be added that AVnu's technology can be applied not only to the automotive industry, but also to professional A/V, industrial and consumer electronics.

4 Conclusion

As cars become more intelligent and networked, automotive electronics will become more complex and their demand for bandwidth will increase. Based on the already mature Ethernet technology, the car Ethernet can meet the new requirements of automotive electronics and provide reliable, mature, low-cost and standardized solutions. It will have a broad space for development in the future. Due to space limitations, this article involves some technical and standardized content that has not been expanded.

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