and receive data in both directions at once. Going above
the PHY chips to the MAC interface level, we find plain-vanilla IEEE 802.3 Ethernet. Thus, the only difference
between BroadR-Reach and ordinary Ethernet is from
PHY to PHY. At the upper levels of the Ethernet stack,
the topology is identical to that of 802.3.
What are some prominent applications for BroadR-Reach? One is ADAS, which can be implemented in
passive or active fashion. A passive ADAS system only
provides drivers with a warning or alert if, for example,
they stray outside of their lane. In contrast, an active
ADAS goes beyond a warning, taking control to perform
a corrective action (returning the vehicle to its lane or
performing automated emergency braking). Another
passive ADAS application is backup cameras; an active
ADAS provides parking assistance.
At 100 Mb/s, BroadR-Reach is best suited for passive
ADAS applications. Active ADAS requires lossless
video so that image-recognition algorithms can function
appropriately. For example, if the vehicle is trying to
recognize potential hazards in the near distance, the
algorithms will focus more accurately with full lossless
Another popular application for BroadR-Reach is
infotainment. BroadR-Reach is more cost-effective than
MOST or low-voltage differential signaling (LVDS).
Much of the cost savings is in the cabling. LVDS cables
are quite thick, so that means higher cost as well as
more weight. LVDS was used often with analog cameras
connected with coaxial cables. With the move to digital
cameras, BroadR-Reach offers the benefits of the twisted-pair cable and higher bandwidth.
100Base-T1 is the IEEE’s specification for 100-Mb/s
automotive Ethernet. You might see it referred to as IEEE
802.3bw, but both names address the same specification.
The “-T1” appendage is an important distinction that lets
you know the name refers to automotive Ethernet, which
is distinct from 100Base-T.
The -T1 variant is interoperable with OPEN Alliance
BroadR-Reach. They are very nearly identical (the names
are often used interchangeably), but for two small
exceptions. In the physical-layer electrical (physical
medium attachment or PMA) test suite, the 100Base-T1
specification defines a test for the maximum Transmit
Peak Differential Output. This parameter is not explicitly
defined in the BroadR-Reach specification.
The second exception is that the 100Base-T1
specification has some differences in the protocol timing
for wake-up commands to make those periods shorter.
But those are the only differences worth noting.
Why, then, one wonders, did the IEEE 802.3bw
specification come about? The driver wants applications
for automotive Ethernet in other application domains,
such as industrial automation and avionics. The benefits
of BroadR-Reach were enticing enough for the IEEE to
create its own version of the specification. As a result,
the two automotive Ethernet specifications share a
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Figure 3: BroadR-Reach differs from IEEE 802.3 Ethernet only
from PHY to PHY; they’re identical at the MAC level.