Successfully Rolling Out Power Over Ethernet

By Sandra Gittlen | May 10, 2006 | Print this Page
http://www.enterprisenetworkingplanet.com/netsysm/article.php/3605291/Successfully-Rolling-Out-Power-Over-Ethernet.htm

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 says.

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 requirements.''

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.

Future-Proofing

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 Jose, Calif.

''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.

Article courtesy of Datamation