Decentralized - Fixture Centric
Pros Cons
• Reduced Day 1 cabling
CAPEX
• Minimal connections
• Limited to 10/100 Mb/s
• Requires AC power at
remote switches
• Difficult to administer
• Limited support of MAC
activity
• Limited support of future
IB applications
• Limited use of structured
cabling
• Network security access is
compromised
• Additional connection point
TABLE 4: Pros and cons of the
decentralized-fixture centric architecture.
January/February 2019 I27
model, a digital building switch is placed between the
TR and the nodes and devices to provide the processing
power closer to the end device. This works well for LED
lighting, but it is limited in bandwidth so may not be
suitable for WAPs or high-resolution security cameras.
In addition, these digital building switches require an
AC outlet. A zone cabling topology can be utilized with
either a centralized or decentralized set up and offers the
greatest flexibility for adding more devices later, which
becomes key when installing cabling infrastructures
to last into the future. There are pros and cons to each
scenario (see Tables 2-4), and the system designer needs
to weigh each to select the layout that best suits
the environment and growing needs of the end user.
“One of the biggest challenges is for the low-voltage
installer to understand these different architectures
because it varies between device manufacturers, as there
are no device standards like there are for the network
infrastructure,” states Luis Suau. “For example, looking
at LED lighting, one manufacturer might use category
cabling directly to the fixture with an RJ45 connection
or plug, whereas others have their own unique layouts
to a node, or a driver,” Suau further explains. “In these
layouts, they are using structured cabling to the node or
driver and then delivering power and serial data through
an 18/2 cable 18 AWG, two-conductor cable that can
FIGURE 11: Decentralized-fixture centric architecture.
be daisy chained to control devices, such as the lights
and sensors and other fixtures,” he adds. “And, most
importantly, the installers will need to understand how
to set up the power source equipment, the switch.”
“The number of total devices powered by the node is
determined by the amount of power from the port. With
60 W at the PSE we could power up to 9 devices. The
node has 2 outputs for lighting and each can power three
lights daisy chained via RJ45 connection for a total of six
fixtures. The third output for controls can power up to
three different control devices,” states Wendell Strong,
GENISYS PoE lighting manager. “Since ‘node centric’ is
different from fixture centric designs, it’s very important
that the installer rely on the device manufacturer for help
in the design and installation,” he adds.
WHERE’S THE BEEF?
“When we are talking lighting, HVAC and other building
applications that were previously installed by electricians,
who makes the decision for the installation when PoE is
involved?” asks Alan Hill, president of Tera Bridge, who
has been involved in many intelligent building designs
and installations. “Since we are basically a design/build
integration company, we are involved up front to show
end users and architects the value of integrating power
and data. Showing real OPEX and CAPEX savings and