Why Automotive Ethernet?

Figure 1: The MOST infotainment protocol offers a higher
aggregate bandwidth than Automotive Ethernet, but its 150-Mb/s
bandwidth is shared across the network

In recent posts, we've been reviewing the subject of Automotive Ethernet in general and the BroadR-Reach protocol in particular. In today's installment, let's look at some of the benefits of using the protocol while comparing it to some other protocols that see usage in the automotive environment.

Automotive Ethernet provides higher bandwidth data transmissions compared with such protocols as LIN (19.2 kb/s), CAN FD (15 Mb/s), FlexRay (10 Mb/s), and MOST (25, 50, or 150 Mb/s shared). The LIN protocol really only sees usage for very low-bandwidth applications controlling body electronics such as windows or lights.

CAN and/or CAN FD offers a flexible data rate in the 15-Mb/s range but still is limited to relatively low-bandwidth applications. The same is true of FlexRay, which does offer the advantage of redundancy with its pair of parallel data lines. If one line is damaged, the other can take over its function. Thus, it has applications in safety or mission-critical functions such as steering or braking control.

MOST is an infotainment standard with data-rate variants of 25, 50, and 150 Mb/s. The latter is a higher aggregate bandwidth than the 100 Mb/s of Automotive Ethernet. But a key distinction is that MOST's 150 Mb/s is shared across the ring-topology network, while each dedicated Automotive Ethernet link provides the full 150-Mb/s bandwidth (Figure 1).

Thus, Automotive Ethernet offers higher bandwidth than do most of the prevalent automotive serial-data standards. Being that it relies on a single unshielded twisted pair, it also provides a low-cost cabling scheme. Cabling weight is about 30% less than shielded cabling with connectivity cost savings of about 80%.

Automotive Ethernet meets the stringent EMC and EMI requirements as well as the temperature-grade requirements of the automotive application space. A final benefit is that all of the software interfaces for the upper layers of the Ethernet stack are exactly the same as for standard Ethernet. If you've ever worked with Ethernet in the past, you'll probably already have all of the software and test tools covered.

Next time, we'll look at BroadR-Reach in comparison with 100Base-T1 and also see what's coming in the foreseeable future for Automotive Ethernet.