Power (Over Ethernet) to the People

802.3af specification will lead to far-reaching cost savings.

Power over ethernet is going to fundamentally change the way LANs are used in the next three to five years by substantially lowering WLAN installation costs and removing one of the key barriers to VOIP implementations.

The recent ratification of the POE standard will unleash a slew of new devices on IT managers. Accommodating these devices and applications will require strategic planning, but the benefits will likely be far-reaching.

POE, known more formally as the IEEEs 802.3af specification, defines a standard way for data terminal equipment to be powered over Media Dependent Interface, or MDI. The POE standard was published—the IEEEs equivalent of bestowing sainthood—in July, but a trickle of 802.3af devices started showing up well before then.

POE will have the most direct and immediate benefit in the areas of wireless LANs and voice over IP. The spec makes it possible for IT managers to confidently install WLAN APs (access points) and IP telephone handsets without regard to the manufacturer of the PSE (Power Sourcing Equipment). Of course, IP telephone handsets are still functionally tied to specific vendors. However, any midspan power injector will work, as we saw in eWEEK Labs interoperability tests with Alcatel Internetworking Inc.s E-reflex model 4210 and PowerDsine Ltd.s 6012.

The 802.3af spec can be used in both 10/100M-bps copper networks and over Gigabit Ethernet copper connections. (There is no way to conduct electricity through optic cables.) Power is supplied in one of two ways: over the spare wire pair (numbers 4, 5, 7 and 8) or "floated" over the data, with data and power transmitted on the same pair. Because PDs (powered devices) are required to accept power using either method, network managers likely wont need to be concerned with which method is used.

The exception is with Gigabit Ethernet, which makes use of the spare pair. However, this shouldnt be a concern for years to come because devices that generate gigabits of traffic will likely need far more power than can be supplied by 802.3af PSE.

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