For Donna VanHousen, senior director of IT at ViaHealth in Rochester,
N.Y., Power over Ethernet (PoE) has been a godsend. But she warns that
ignoring best practices for this new technology could create a nightmare.
VanHousen is in the midst of a wireless rollout at two hospitals that are
part of the ViaHealth regional healthcare delivery system. ”When we
looked at powering all the access points, we would have had to install
outlets at each location,” she says.
The cost for electricians to do the outlet installations would have
skyrocketed project costs. Instead, VanHousen decided to use PoE (IEEE
802.af standard), which transmits power from switches to devices over
traditional twisted-pair copper cabling.
She realized that a future IP phone rollout, as well as other wireless
technologies, throughout the hospital system, including I.D. card
readers, intercom networks and security cameras, could all take advantage
of her PoE project.
Putting all the power into the wiring closet holds tremendous
opportunity, but it also poses significant risks. ”Suddenly you have a
single point of failure if not done correctly,” she says.
Mike Hronek, networking engineer at technology retailer and consultancy
CDW Corp. in Chicago, agrees. He says planning has to start at the
device-level before anything is implemented. ”The first thing you have
to do is figure out how much power each device is going to draw,” he
This is critical because switches are not designed to draw the same
amount of power. ”For instance, if a device, such as a wireless access
point, draws 15.4 watts of power, a 48-port switch can’t support that
much power to all of its ports,” he says.
He recommends gathering detailed device specifications from vendors and
mapping those to switch capabilities. ”Think about the devices you are
going to have in the future. The life expectancy of a switch is two to
three years so make sure you plan accordingly. You don’t want to have to
swap out your switch,” he says.
While most chassis-based switches allow you to increase power supplies,
Hronek warns that many stackables do not.
Kevin Tolly, founder of The Tolly Group testing firm in Boca Raton, Fla.,
says it’s important to test how the switch handles devices. He says some
PoE chipsets are pre-standard and ”can be uneven in ways that are
difficult to see.”
He recommends using tools, such as those from Sifos Technologies, Inc.,
to ensure that current and future switches are standards-based and can
support the device load. ”You can’t just say I have a PoE chipset in
place on this switch and be done with it. They are all designed
differently. Make sure you drill down and find out exactly what chipset
your vendor is using and how they’re using it,” he says.
He adds that IT groups should work with vendors to secure a guarantee
that their switch will handle your PoE needs or you’ll get your money
back. ”Don’t take the word of the sales representative on this
technology,” he says.
Another consideration for PoE use is the power, heating and cooling
needed in wiring closets to support the switches.
”A big gotcha for PoE is within the wiring closet,” says Brian Witt,
director of product marketing at Alcatel in Calabasas, Calif. ”A lot of
wiring closets were built around low-power supply and cooling
Witt says it’s critical that when building PoE into your network, to
leave some time to improve power and cooling to each closet. ”You have
to do power conditioning and battery backup,” he says.
She says IT groups should meet with physical plant staff to determine
whether the HVAC system that controls the temperature in the wiring
closets and overall power capacity is adequate for the new levels. ”You
have to account for all this — our usage did go up so engineering had to
come in and upgrade the closets,” she says. She adds that IT should ask
vendors for the BTU requirements of switches. She also recommends
reviewing your plans for an uninterruptible power supply system.
Redundancy is also mission-critical, according to Hronek.
If a switch goes down, you want to make sure your devices can still
operate. You can do this in several ways — backup power, redundancy
between switches and wiring closets, and priority settings within
switches. He says some POE-enabled switches offer the ability to select
what devices stay powered in the event of an outage and users should plot
this out carefully. For instance, you can mark certain IP phones to stay
powered during an outage so that employees can make emergency calls.
While today’s PoE standard is set to support devices needing 15.4 watts
or less, new efforts are under way to boost that limit, according to
Madhu Rayabhari, vice president of marketing for PowerDsine, Ltd., in San
”While 15.4 watts is adequate for many common applications, there is a
need for even greater power. Therefore, not all applications can benefit
from power over Ethernet today. But the new standard — IEEE 802.3at —
will scale up to address high-power peripherals of approximately 50
watts,” he says.
Rayabhari says the next-generation standard should be available within 12
to 18 months.