The unsung hero behind in-car communications in next-generation vehicles | What is Ethernet? | NEXTY Electronics, an electronic components and semiconductor trading company

In recent years, vehicles have become increasingly electrified, with ECUs (Electronic Control Units) being installed in various parts of the vehicle, OTHERS the engine, body, and control systems. Each ECU interconnects and communicates over an in-vehicle network. As vehicles become more powerful, in-vehicle Ethernet with communication speeds of several Gbps is being considered for the future.

Automotive Networking

Conventional in-vehicle network

Vehicle communication protocols include CAN (Controller Area Network), LIN (Local Interconnect Network), MOST (Media Oriented System Transport), FlexRay, and CAN FD, of which CAN and LIN are the most commonly used.

CAN communicates at a maximum speed of 1Mbps using a multi-master method, which means that each ECU can start communication when the CAN bus is free.
LIN communicates at a maximum speed of 20kbps using a master-slave method.
The master-slave method is a method of dividing the roles of ECUs connected to the LIN bus, with one acting as the manager and controller and the rest as the controlled ones. Although LIN has a slow communication speed, it has the advantage of being inexpensive.

A gateway ECU is used to communicate between different communication protocols. Communication that passes through multiple gateways can cause data delays. To prevent delays, a central gateway (CGW) integrates each gateway and connects each functional system to a single gateway.

Future in-vehicle networks

Currently, autonomous driving, ADAS, and IVI are being developed, but from the perspective of communication speed, it is extremely difficult to realize ADAS and IVI functions using only the CAN and LIN protocols.In order to solve problems such as the increase in communication data volume due to improved sensor resolution and the increasing complexity of in-vehicle networks due to the increase in the number of ECUs installed, in-vehicle networks that place a high-performance main ECU in the center of the vehicle and zone ECUs for each area are attracting attention.

Ethernet has been adopted to connect each ECU in this network, and there is growing interest in in-vehicle Ethernet, which can realize next-generation in-vehicle networks with high bandwidth and low latency.

Ethernet

Ethernet is a standard for wired LANs (Local Area Networks) that allow computers and network devices to communicate with each other. It is primarily used indoors and within buildings such as factories. Ethernet offers advantages such as high-speed transmission, noise resistance, reliable data transmission, and relatively low cost. These advantages have made Ethernet a widely used standard network standard (IEEE802.3). Compared to other communication technologies, it is superior in versatility, speed, reliability, economy, and flexibility, and is therefore used in many environments.

IEEE802.3

IEEE802.3 is an international standard for LANs (Local Area Networks) and MANs (Metro Area Networks). It defines the specifications for the MAC (Media Access Control) that controls communication within the network, and the database that stores network status and settings. In the data communication section, it defines the Ethernet protocol FRAMES.

It also defines the MII (media-independent interface) that communicates between the MAC layer and the PHY of the physical layer device, OTHERS the control/management protocol and power supply.

General notation

Because there are many types of Ethernet, they are given standard names that allow you to identify their functions at a glance. Generally, the physical layer is named using the following notation:

<Data rate> <Modulation method> <Details>
〈100〉〈BASE〉〈-TX〉

The data rate is in Mb/s if it is just a number, and in Gb/s if it has a "G" at the end.
The modulation method indicates how the encoded data is transmitted over the medium. The baseband modulation method "BASE" is mainly used. Details indicate the characteristics of the transmission and the medium. "T" indicates twisted pair CABLES, "T1" indicates single twisted pair CABLES, and "B" indicates bidirectional optical fiber.

Differences in transmission methods

1000BASE-T1 is an established standard for in-vehicle Ethernet. 1000BASE-T1, 1000BASE-TX, and 1000BASE-T use different information transmission methods.

1000BASE-T1 transmits data at 1Gbps over a single twisted pair CABLES. CABLES can transmit and receive data in both directions.

1000BASE-TX transmits data at 500Mbps over a single twisted pair CABLES. Of the four twisted pair CABLES, two are used for transmission and two for reception.

1000BASE-T transmits data at 250Mbps over a single twisted pair CABLES. CABLES can transmit and receive data, and four twisted pair CABLES can transmit data in both directions at the same time.

Automotive Ethernet

Communication method

PHY standards for in-vehicle Ethernet include 100base-T1 and 1000base-T1. These are specified in IEEE802.3bw and IEEE802.3bp. Both communicate between PHYs at 100Mbps or 1Gbps over a single twisted pair CABLES. Major differences from consumer Ethernet include reduced EMI, guaranteed operation in harsh environments, low power consumption, and longer CABLES lengths.