Powering Up Ethernet

802.3af sparks savings and simplifies wiring and management.
“The cost to use PoE over the data cable, about $150 to $175 per drop, was less than half the cost of separately cabling for data and power,” says Gary Arstein-Kerslake of California’s EPA.

California’s Environmental Protection Agency and the city of Keene, N.H., are among the organizations increasingly tapping Power over Ethernet (PoE) to reduce costs and simplify wiring.

The Institute of Electrical and Electronics Engineers 802.3af standard for PoE transmits electrical power over the same twisted-pair wiring that carries data. The technology has obviated the need to hire expensive electricians each time the EPA adds a wireless access point or a Voice over Internet Protocol (VoIP) phone in its 25-story building.

PoE shipments are forecast to grow from 32 million ports in 2006 to 145 million ports in 2011, according to IT research firm Dell’Oro Group in Redwood City, Calif.

Before investing in the technology consider your energy requirements, potential costs and savings, and network management benefits.

Energized Equipment

The 802.3af standard can accommodate only low-powered devices that use 15.4 watts or less, such as wireless access points and stationary Web cams. But that is expected to change in 2008 with the IEEE adoption of the 802.3at standard, also known as PoE Plus. Then, 30-watt devices, such as swivel security cameras, can be used.

PoE devices often consume more power than non-PoE devices do. For example, when a 48-port non-PoE network switch is replaced with a PoE switch, the power consumption leaps from 265 watts to 1,150 watts.

Cost Considerations

Next, evaluate your equipment budget. PoE-compliant wares, such as switches, carry a slight premium over non-PoE gear — often 10 percent to 15 percent. However, the extra cost is typically overcome through the installation savings PoE generates. “If you are implementing Wi-Fi, PoE has a lot of advantages,” says Gary Arstein-Kerslake, information technology officer with the California Environmental Protection Agency. “The cost to use PoE over the data cable, about $150 to $175 per drop, was less than half the cost of separately cabling for data and power. It yielded a savings of about $200 per drop.”

In its case, the EPA installed a 24-port PoE-compliant Cisco Catalyst switch for 20 VoIP phones, and 70 Cisco Aironet power injectors to bring electricity to non-PoE wireless access points. Power injectors, typically installed near the Ethernet hub, inject DC voltage onto the Ethernet cable. Access points and other devices that are PoE compliant can then pick up the DC voltage through their RJ-45 jack.

More important, PoE boosts productivity. “Now, someone can pick up the phone from their desk and walk into a conference room if they need to work there,” says Rebecca Landry, Information Management Services director for Keene, N.H. Late last year, the city finished installing 300 3Com VoIP phones that use PoE across a Cisco network.

Management Means

Finally, factor in whether your organization can benefit from PoE’s security, efficiency and redundancy benefits. Using simple network management protocol, network administrators can monitor and control powered devices — including shutting them off if there is a security breach. The Cisco Catalyst 3750-E Series Switch, for example, allows customers to specify the maximum power setting on an individual port. Similarly, Hewlett-Packard’s ProCurve Switch 2626-PWR offers 802.1X and RADIUS network login to control port-based access for authentication.

“Overall, we’re pleased,” says Landry. “Power over Ethernet has made things easier.”


The savings California EPA has reaped since 2005 from moving to PoE installations.

PoE Pumps Up

Sometime next year, the Institute of Electrical and Electronics Engineers is expected to approve the 802.3at standard, often referred to as power over Ethernet Plus (PoE Plus). The standard aims to allow higher powered devices, such as radio frequency ID sensors, video screen phones and pan-tilt-zoom cameras, to use PoE.

Among the tasks of the IEEE PoE Plus study group is to ensure that existing Class D/Cat 5e cabling (or better) infrastructure will work in conjunction with 802.3at. Manufacturers have begun to release “pre-compliant” PoE Plus equipment, though there’s no guarantee it will work with the resulting standard.

Sep 26 2007