Power-over-Ethernet technology (PoE) allows IP telephones, wireless LAN access points, webcams and many other appliances to receive power as well as data over Ethernet protocol, using the existing LAN cabling.

Also, with the power-over-Ethernet (PoE) technology coming into play, wireless access points and other such devices will need structured cabling as the underlying infrastructure.

The technology works by injecting DC-converted power over the spare pairs of Cat 5 and above cables. Various WLAN equipment and end-user devices including laptops and VoIP phones can then be plugged into the cable to draw DC power. PoE, as one can see, converges not just telephony and Internet-but also power-on a single medium, copper.

It also addresses the problem of an IP call getting disconnected in the event of a general power failure.

The growth in PoE is directly linked to the rapid growth in IP-based applications (telephony and video) as also wireless LAN protocols. The case for providing PoE through the structured cabling system is based on the fact that provision of power should be done in a transparent (non-interfering) manner. The passive solution lends itself to such a transparent provision as long as power is injected over the non-data carrying pairs in the UTP cabling, and as long as the device used for injecting power does not have the potential to interfere with sensitive switches and patch panels.

IEEE 802.3af defines requirements for PoE. This currently calls for a consistent provision of 15.4 watts of power to all IEEE-compliant powered devices (PDs). PDs listed include IP phones, IP cameras, WLAN access points, access control devices, etc.

The freezing of the 802.3af standard will allow an explosion of PoE devices and installations. The PoE standard has the potential to change the way IT deploys big applications. For many IT managers, starting now to plan for PoE will pay dividends later.

While evaluating options for PoE, network managers should keep the following considerations in mind:

• Does the PoE device have the potential to create interference or is it transparent?
• Does it have modularity and hot-swappable features (think of a situation wherein multiple users have to be switched of because one module conked off!)?
• Does it have a standards compliant (IEEE 802.3af) power management system and a 'handshake' protocol? The latter ensures that PoE is supplied only when a suitable device is available at the other end to receive this and function. Device detection prior to activating power prevents the device damage.
• Is the PoE solution manufactured in-house by the structured cabling vendor, versus an outsourced module with the accompanying issues of support?