What is Ethernet

These days, we often hear the word "Ethernet." Ethernet is a communication standard for connecting devices such as computers via wired connections to send and receive data. It is commonly used in offices and homes to build LANs and for data communication between devices, such as over the internet. This Ethernet is now attracting attention as one of the network technologies installed in automobiles. We will provide a comprehensive overview of Ethernet, including the background behind its introduction as an in-vehicle network and an overview of the standard.

Background of the introduction of in-vehicle Ethernet

The introduction of Ethernet as an in-vehicle network is driven by advancements in technologies such as AD/ADAS, electrification, and connectivity. In the future, automobiles are expected to become even more autonomous driving and electrified while remaining connected to external networks, and consequently, the architecture of in-vehicle systems that connect ECUs, sensors, actuators, and other components is also poised for significant changes.
 
Due to changes in architecture, the following trends are emerging:
- From distributed processing to centralized processing
Increase in the amount of data transmitted
Dynamic system updates
 
This has created a need for a way to deliver large amounts of information more quickly to those who need it. In the future, the amount of information transmitted from cameras and sensors is expected to increase to several gigabits per second, and the current CAN communication speed, which is the mainstream in-vehicle network protocol, will not be able to keep up. Against this backdrop, attention is growing on in-vehicle Ethernet, which is capable of high-speed and high-capacity communication.

Image of the positioning of the in-vehicle network

Here is an illustrative diagram showing how Ethernet can be used in in-vehicle networks.

Figure 1. Positioning of Ethernet​

Ethernet 's positioning is expected to be adopted to enable faster communication speeds and large-capacity data transfer, driven by advancements in AD/ADAS and connected technologies. In comparison to conventional communication methods, protocols such as CAN and LIN are commonly heard of in automotive communication.
 
Due to its high reliability and dependability, CAN is widely used in automobiles, primarily in control areas such as the engine and brakes. While it has been adopted in various fields outside the automotive industry, its maximum communication speed is 1 Mbps, making it unsuitable for transmitting large amounts of data, such as video processing.
 
LIN has a low communication speed of up to 20kbps, but it can be implemented at a lower cost than CAN. For this reason, it is often used to control body systems such as mirrors, door locks, and power windows.
 
Thus, considering that CAN has a maximum speed of 1 Mbps and CAN FD has a maximum speed of 8 Mbps, Ethernet 's communication speed is very attractive.

Comparison with conventional networks

For comparison with conventional networks, we have summarized the differences between CAN, LIN, and Ethernet in the table below.
When comparing Ethernet with CAN and LIN, it becomes clear that there are many differences in various aspects besides communication speed, such as topology, communication range, communication method, cable, and features, and that Ethernet offers many advantages compared to other communication methods.

*This description includes Ethernet, including consumer-grade Ethernet.
Figure 2. Comparison of network configurations

What is in-vehicle Ethernet?

Here, it is used in vehicles Ethernet Let's take a look at the standards.
  
In-vehicle Ethernet This is for consumer use in homes and offices. Ethernet This is an optimized version for automotive use. Ethernet As a standard, 100BASE-TX However, 100BASE-TX There were several challenges in using it directly in a vehicle. The main challenges are listed below.
- The cost of communication wires is high.
- Narrow operating temperature compensation range
- It is prone to generating noise and is susceptible to external interference.
・ Sleep The standby current is large.

The standard developed to address these challenges is the automotive Ethernet standard (100BASE-T1).

Differences between consumer and automotive Ethernet

The table shows the differences between 100BASE-T1, which was developed for automotive applications, and 100BASE-TX, which is for consumer use.
I'd like to highlight some of its distinctive features.

*1: If compatible with OPEN Alliance TC10
Figure 3. Comparison of consumer Ethernet and automotive Ethernet.

 
First, regarding the communication speed, it is 100Mbps, the same as the consumer-grade 100BASE-TX. Next, regarding the encoding method, while MLT3 is used for consumer applications, PAM3 is used for automotive applications instead, as it reduces rise time and EMI. PAM3 is a three-level pulse amplitude modulation method.
 
Regarding the operating range, 100BASE-T1 for automotive applications is specified as operating from-40°C to 125 °C, which is the automotive grade. The cable length is shorter compared to consumer Ethernet.
 
While consumer Ethernet cables designed for office environments are typically 100m long, automotive Ethernet cables are used in harsh environments, requiring shorter lengths of 15m to account for wiring space and noise interference within vehicles. The number of intermediate connectors is also specified, with a maximum of four.
 
Finally, regarding cables, while consumer Ethernet specifies two twisted-pair cables, 100BASE-T1 for automotive applications specifies a single twisted-pair cable. This significantly reduces cable costs and weight. The biggest advantage of the 100BASE-T1 standard, which was developed for automotive applications, is that it allows communication using a single twisted-pair cable.

The position of Ethernet in the OSI reference model

Up until now, we've been using the term "Ethernet" as if it were common knowledge, but what exactly is "Ethernet"?
This presentation will use the OSI reference model to explain the positioning of the Ethernet standard.

Figure 4. OSI Reference Model

 
The OSI reference model is a framework for understanding and designing network communications in a hierarchical manner, with each layer playing a different role. Many people generally think that Ethernet includes TCP/IP. However, in reality, only the first layer, the physical layer, and the​ ​second layer, the data link layer, of the OSI reference model correspond to "Ethernet" as defined in IEEE 802.3.
 
The role of the first layer, the physical layer, is to convert digital data received from the data link layer into physical signals and transmit them via a transmission medium (physical medium, copper wire, optical fiber, etc.). It also performs the reverse role. The second layer, the data link layer, is located between the physical layer and the network layer and acts as a bridge to ensure accurate data transmission.

physical layer

The physical layer in Ethernet is called the EthernetPHY. Ethernet PHYs are standardized according to differences in transmission medium and transmission speed. 100BASE-T1 and 100BASE-TX are examples of this. In automotive Ethernet, in addition to 100BASE-T1, 1000BASE-T1 (1 Gbps) and 10BASE-T1S (intended for sensor/actuator applications) are also standardized.

Figure 5. Features of the Ethernet standard

data link layer

The data link layer acts as a bridge between the physical layer and the network layer, ensuring accurate data transmission. It frames data and adds header information (such as destination and source MAC addresses) to ensure accurate delivery to the target device. Furthermore, it enhances communication reliability through error detection.

Figure 6. Ethernet frame

Ethernet frames range in size from 64​ ​to 1518 bytes. In Ethernet, 8 bits are called octets, not bytes. There are two Ethernet frame formats: the "Ethernet II standard" and the "IEEE 802.3 standard." The format shown above is the "Ethernet II standard," and it consists of five feeds: preamble, destination / source MAC address, type, data, and FCS. These together are called the "Ethernet header."
 
The preamble is a special 8-byte bit pattern that signals, "I'm about to send an Ethernet frame!" Specifically, it consists of "10101010" repeated seven times, followed by "10101011". The receiving terminal sees this special bit pattern at the beginning of the Ethernet frame and determines that an Ethernet frame is about to arrive.
 
Next are the destination / source MAC addresses. The sending terminal sets the destination MAC address of the terminal it wants to send the Ethernet frame to and its own MAC address as the source MAC address, and then sends out the Ethernet​ ​frame. The type is a 2-byte ID that indicates what protocol is being used at the network layer. For example, it is "0x0800" for IPv4 and "0x86DD" for IPv6, and the value is determined by the protocol and version being used. The Ethernet payload stores data for higher-level protocols such as IPv4, IPv6, and ARP. In the case of IP communication, the IP packet becomes the Ethernet payload. In packet switching, data is not sent as is, but is divided into packets to make it easier to send.
 
Finally, there's the FCS. The FCS is a 4-byte field used to check if an Ethernet frame is corrupted. It checks the destination / source MAC address, type, and data, and the result is appended to the end of the frame as the FCS to determine if it's correct. If it's incorrect, the Ethernet frame is considered corrupted and discarded.

About the Renesas product lineup

Some Renesas products are equipped with Ethernet. We have devices available that can be used in vehicles, so please contact us.

Renesas Electronics Automotive SoC R-Car Family - Renesas -Macnica

Renesas Electronics Automotive MCU RH850 Family - Renesas -Macnica

Contact Us