Cabling feels the power

A developing technology known as Power over Ethernet is catching on with organizations looking to cut costs on wireless LAN deployments. It also can keep IP phone users talking even if the lights go out.

Some users already have discovered that powering Wi-Fi access points with PoE can save hundreds, even thousands, of dollars per installed device by eliminating costly power-outlet installations. Meanwhile, early adopters of IP PBXs and phones say PoE is an indispensable way to provide dial tone during power outages, a common feature on legacy PBXs that the voice over IP market was slow to adopt.

PoE, an IEEE standard since June, is available on switches from almost every major LAN infrastructure vendor, and IP telephony and WLAN equipment companies. Most vendors offer PoE switches that are based on the IEEE 802.3af standard. Cisco Systems Inc. offers a proprietary PoE technology for its IP phones, switches and Wi-Fi gear, and 802.3af-based products.

The IEEE 803.3af standard defines two methods for delivering up to 48 volts of DC power to PoE-compliant devices over eight-wire Category 5 and 6 cabling. One is called mid-span, which involves running power over unused wire pairs in a LAN cable. (Only two of the four pairs are used to deliver data in Ethernet and Fast Ethernet.) Mid-span products from the company PowerDsine often are built into patch panel-like devices that can add PoE to existing LAN infrastructures.

The other, increasingly popular version of 802.3af is called end-span. It runs DC power signals over the same wire pairs used for data transmission, but at different frequencies than Ethernet signals. Industry experts say end-span devices are becoming popular because they usually are built into new switches with PoE, which users often buy for IP telephony or WLAN rollouts. End-span also allows Gigabit Ethernet and PoE to co-exist as 10/100/1000Mbps links become more popular. (Netgear Inc. this week announced a triple-speed Layer 3 switch with PoE at Comdex.)

PoE has become a hot complementary technology for WLANs. Several makers of wired and WLAN gear now offer 802.3af-compliant access points and switch ports; they include 3Com Corp., Airespace Inc., Aruba Wireless Networks Inc., Cisco, Extreme Networks Inc., Hewlett-Packard Co. and Nortel Networks Inc.

One benefit of using PoE with Wi-Fi is that it eliminates the need to have electricians install new power outlets to support large-scale WLAN deployments. This benefit becomes quickly obvious in very large-scale WLAN access point deployments, such as on big university campuses.

Purdue University in West Lafayette, Ind. recently rolled out 1,100 WLAN access points to provide connectivity to 140 buildings and 40,000 students. This project involved sticking WLAN access points in unusual places, according to Brad McCoy, network engineer for IT at Purdue. For example, the devices were fitted under ceiling tiles in the middle of classrooms, in hallways and in cafeterias. It was hard enough for McCoy’s staff just to pull Category 5e cabling to such spots.

“We would have run significantly higher costs trying to power this wireless network” if AC outlets had to be installed for each access point, McCoy says.

McCoy saw PoE as the answer, but was not interested in swapping his LAN wiring closet infrastructure for new PoE switches. Instead, he installed PowerDsine 6012 Power over LAN hubs. Wherever WLAN access points need to be supported on campus, the PowerDsine hubs sit in front of wiring closet LAN switches and run 803.3af power over the network drops. McCoy estimates that the PoE setup helped save the school between US$350 to US$1,000 per access point installed because new AC outlets were not necessary.

Power of VoIP

While PoE helps users reduce costs of WLAN deployments, the technology also is becoming a standard component of many enterprise IP telephony projects. Many organizations took for granted that their PBX system also provided power to desktop phones and voice connectivity. In early IP PBX systems, this was not the case; IP phones required their own power source, which made the devices as vulnerable as PCs, ceiling lights or anything else plugged into an AC outlet during a power outage.

The North Hunterdon-Voorhees Regional High School District in New Jersey recently installed PoE switches from 3Com to support its 3Com NBX phone system. The school has 700 phones deployed to the desks of school administrators and to all classrooms in its two high schools.

To ensure that phone service stays available during an emergency, the school deployed 3Com SuperStack 3 Switch 4400 PWR switches to all its wiring closets. These switches and the NBX IP PBX are hooked to uninterruptible power supplies that let the phone system deliver dial tone to IP phones for about three hours in a blackout.

The 3Com phones include a two-port 10/100Mbps switch, letting a desktop PC be connected to the LAN phone through the IP phone’s switch port. This, says Rich Bergacs, director of technology for the school district, made deployment less costly because no new LAN cables had to be run to desktops or to classrooms.

While the school district sees no direct savings from running PoE to its IP phones, Bergacs says the payoff comes with the peace of mind from having a more reliable phone system.

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