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14 June 2021

Automotive Ethernet in the Vehicle

Figure 1 Block diagram of a typical ADAS system
showing the in-vehicle networks used.
As all Automotive Ethernet technologies utilize a single twisted-pair cable (T1) and a point-to-point network topology, they differ primarily in their data rates and encoding methods. For the most part, the data rate determines the applications for which a particular Automotive Ethernet standard can be used. If we take the case of an automatic driver assistance system (ADAS), we can see where each Automotive Ethernet variant might best be used to replace existing automotive protocols. 

(Click on any figure to enlarge the image.)

10Base-T1S

Figure 2: 10Base-T1S is best used for lower
bandwidth communications from sensors and ECUs.
10Base-T1S is a 10Mb/s Automotive Ethernet described in the IEEE 802.cg standard. It is intended for 10-to-25-meter, short-reach applications. 

Using differential Manchester encoding (DME), all physical layers employing 10Base-T1S must support the point-to-point topology up to a 15-meter reach, with full duplex operation. 

Multidrop is an optional topology for 10Base-T1S, where eight or more nodes can be supported on a maximum bus length of 25 meters. 

10Base-T1S is best used for lower speed data communications between power train ECU’s, sensors, car body ECU’s, and audio transducers like speakers and microphones (Figure 2). Here, it would replace traditional in-vehicle networks like CAN, LIN or FlexRay, removing the need to manage multiple technologies and simplifying designs. 

100Base-T1 

Figure 3: 100Base-T1 is used for applications
requiring moderate data rates, such as
infotainment and passive ADAS systems.
100Base-T1 is a 100 Mb/s Ethernet standard described in IEEE 802.3bw. It was originally specified by Broadcom as BroadR-Reach. 100Base-T1 uses PAM3 encoding, full-duplex communication and a point-to-point topology.

100Base-T1 is used in applications where moderately high data rates are required (Figure 3), such as infotainment systems, where it replaces exiting technologies such as MOST and LVDS that use heavier and more expensive cabling. It could also be used in Passive ADAS operations, such as lane departure warnings and backup cameras.  

1000Base-T1

Figure 4: 1000Base-T1 is used in applications
where the high data rate is essential, like
active ADAS or as the communications backbone.
1000Base-T1 is 1 Gb/s Automotive Ethernet described in IEEE 802.3bp. Like 100Base-T1, it uses PAM3 encoding, full-duplex communication and a point-to-point topology. 

The higher data rate of 1000Base-T1 is suited for active ADAS, systems such as lane departure assistance or automated emergency braking (Figure 4). In these applications, the systems are connected to actuators and can take control of the vehicle. It can also be used as the communications backbone, a virtual “highway” for in-vehicle data transfer.  

MultiGBase-T1

MultiGBase-T1 provides the highest bandwidth of Automotive Ethernet variants (so far) to support high-speed applications. It is defined in IEEE 802.3ch for three data rates: 2.5GBase-T1 at 2.5 Gb/s, 5GBase-T1 at 5 Gb/s, and 10GBase-T1 at 10 Gb/s. MultiGBase-T1 utilizes PAM4 encoding, full duplex communication and a point-to-point topology. 

Figure 6: MultiGBase-T1 is used for very high data rate
applications, such as autonomous driving systems.

MultiGBase-T1 enables the high data rates needed for systems associated with autonomous driving (Figure 5). These applications require lossless video transmission to provide high-resolution video for image recognition. Autonomous driving systems are connected to actuators that can take control of the vehicle, and there can be no dropouts in the video stream or other communications.

What’s Next?

25 and 50 Gb/s Automotive Ethernet standards are being developed now in IEEE 802.3cy, scheduled to be released in late 2023, although deployment is not expected before 2030. This variant would be ideal for data transmission to the central system for processing and decision making (sensor fusion module).

Watch Bob Mart describe the uses of Automotive Ethernet in the on-demand webinar, How to Become an Expert in Automotive Ethernet Testing, Part 1.

See also:

Fundamentals of 100Base-T1 Ethernet

Fundamentals of the BroadR-Reach Protocol

Distinguishing BroadR-Reach and 100Base-T1

Introduction to Automotive Ethernet Compliance Testing

Automotive Ethernet Compliance: The Five Test Modes

Debugging Automotive Ethernet Transmitter Output Droop




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