Jul 19 2007

The Power of PoE

Power over Ethernet is a more cost-effective method to deploying VoIP, Wi-Fi and security.

Wouldn’t it be convenient if you could use your local area network cabling to provide power to devices on your network, such as wireless access points (APs), Voice over Internet Protocol (VoIP) desk phones, Web cams and card readers? And wouldn’t it be nice to provide uninterruptible power supply backup to these specific devices rather than to entire power circuits, so if there’s a power failure, you can ensure that your digital desk VoIP phones and wireless LAN service still work?

Good news: You can, thanks to 802.3af — better known as Power over Ethernet (PoE).

PoE allows electrical current to be carried by Ethernet cables rather than by power cords. PoE can deliver slightly less than 13 watts of power (about 350 milliamps of current) over a cable. That’s enough for smaller WAPs and IP phones.

Your existing LAN cabling, including CAT3, CAT5, CAT5e, and CAT6  (“CAT” stands for “Category”), should be adequate to handle PoE without any changes or upgrades. The PoE standards currently support Fast Ethernet (10/100 Mbps) and Gigabit Ethernet (1 Gbps) on endspan devices (midspan injectors supporting Gig-E should be available in the coming year).

Sister companies Net Star Telecommunications, a national ISP, and integrator Southway Systems are using PoE to provide power for the WAPs and VoIP phones not only at their 30-person office but also when provisioning customer sites, says John Agathon, the companies’ vice president of sales.

“We’re usually setting up 10- to 30-person offices, and we use Power over Ethernet almost exclusively for their phones and wireless LANs,” he says. “It avoids the power cable and power strip mess, and it means we don’t have to have AC adapters at each desk.”

Lime Brokerage (www.limebrokerage.com), a direct access brokerage catering to small to midsize hedge funds and professional traders, uses PoE to power VoIP phones for its 35 employees in five offices, according to Chad Cook, vice president of information security.

“We’re using PoE for our VoIP network and for some environment monitoring, and to power environmental sensors [air conditioning and temperature] and power monitoring devices in our [unmanned] data centers,” Cook says. “We selected PoE for ease of management and integration with our existing monitoring tools, and it gives us more remote control over the sensors.”

PoE Products and Trends

Many new network switches and routers — called “endspan” devices because they’re at one end of the LAN cabling — are available in power-sourcing equipment (PSE) versions.

If you don’t want to replace existing network gear, you can either replace your patch panel with a PSE patch panel or add a midspan injector PSE between your switch and patch panel. Midspan injectors usually go in a wiring closet rack. Another reason to consider using midspans is if you need to add power to ports in several of your switches.

Cisco has PSE features in two product lines that work for small companies, according to Fred Weiller, director of switching solutions marketing at Cisco. “Our Catalyst Express 500 product line has a series of options — some have PoE on just four ports, others have PoE on all 12 or 24 ports. These are ideal for networks of 20 to 200 people. And for small or branch offices that don’t need a separate switch, our Integrated Services Router line lets you have PoE ports directly off the router.”

3Com PoE switches include the 3Com Unified Gigabit Wireless PoE Switch, a 24-port managed rack-mountable switch.

Meanwhile, D-Link offers both PoE and non-PoE versions for most of its switches, according to George Cravens, technical marketing engineer, D-Link Systems. For example, DLink’s eight-port DES-1008 unmanaged switch (with four PoE ports) and 24-port DES-1228 Web-managed switch are available with or without PoE.

NetGear’s PoE products include its FS108P ProSafe 8, a wall-mountable eight-port switch, and the FS726TP ProSafe 24-port 10/100 Smart Switch, with 12 PoE ports.

For most companies, D-Link’s Cravens notes, “A Web-managed switch should provide sufficient features and doesn’t require an IT person to administer.”

For companies that need to power only one or two devices, or want to start with a one-device trial, D-Link and Linksys provide single-port PSE adapters, to add power to a single Ethernet run, and “splitters.” The D-Link DWL-P200 PoE Adapter and LinkSys Power over Ethernet Adapter Kit both include a base unit (PSE) and a terminal unit (splitter).

If you’re in need of a line tester, PowerDsine’s Power over Ethernet Tester can test your cabling infrastructure for the presence of power and identify the type of PSE being used.

A growing number of access points, VoIP desk sets, Web cams and other devices are PoE-ready. If you have devices that aren’t, you can buy single-port PoE splitter adapters. Simply connect the cable run to the adapter, and then a short Ethernet cable — along with a power cable with the appropriate tip — to the device.


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