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A Look at POE Plus

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The IEEE's 802.3at standard, known as POE Plus, aims to provide a much-needed boost to the existing 15-watt 802.3af standard. It should provide 30 watts, enough for many devices that currently demand dedicated AC power runs.

Today, the biggest player in the 802.3at arena is Microsemi (formerly Powerdsine); it provides OEM modules for switches as well as midspans that can be added to switches that don't support PoE. The company was prominent in development of the 802.3af standard, and it has had equipment that supports pre-standard versions of 802.3at available for a number of years. All the other players you'd expect, including Broadcom Corp., Texas Instruments and Cisco Systems, are actively participating in the IEEE's 802.3at working group as well.

Like the IEEE's original power over Ethernet spec, 802.3at will be a universal standard. It will roughly double the 15 watts that 802.3af supplies, making PoE feasible for a whole new group of devices.

Let's face it: Modern hardware sucks up as many watts as you can supply. And as video-surveillance devices and POS terminals proliferate with 802.11n APs on the near horizon it's becoming clear that the 802.3af PoE spec won't be able to keep up much longer.

Thankfully, the IEEE is at work on 802.3af's successor, 802.3at. POE Plus promises to about double the wattage of 802.3af, to 30 watts, while also facilitating more dynamic power management, which could save energy and decrease the cost of power supplies.

There are a few obstacles in the way of power supply nirvana, though. For starters, a more dynamic power management scheme relies on a supporting spec that is still being hammered out and may have inherent flaws that can't be overcome. Beyond that, POE Plus will call for additional power in the telecom closet, and UPS and cooling systems may need upgrades.

The Progenitor
While the existing 802.3af standard has made it possible to power VoIP phones, wireless APs, even some cameras over standard Ethernet cabling since 2003, it can't meet the demands of some higher-end devices, including cameras with pan/tilt/zoom capabilities, door controllers and POS terminals. In addition, APs that support the upcoming 802.11n standard will likely require the power of 802.3at, although single-radio 802.11n APs should be able to work with 802.3af. As other devices that previously needed individual power supplies become more energy efficient, they might become candidates for 802.3at as their lower requirements bring them into range of that spec.

Coming Soon to a TeleCom Closet Near You

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In PoE parlance, a Powered Device, or PD, is the term applied to a device that can benefit from PoE. The term Power Source Equipment, or PSE, refers to either a switch with PoE capabilities or a midspan device, also called an injector. Injectors tap into an existing Ethernet connection and introduce power where it is not provided by the switch. The option of using a midspan device is available in both POE and POE Plus. In fact, early PoE Plus adopters are likely to use midspan devices, which should support 802.3at before the spec is supported in switches. Sites are also likely to use one-port versions of midspans where they need only a handful of PoE Plus connections.

Microsemi Corp. (formerly Powerdsine) already has pre-standard versions of PoE Plus products and, according to Daniel Feldman, the company's senior product line manager, it will soon have offerings that are guaranteed to be upgradable to the approved standard when it's finalized; we expect to see other vendors offer upgradable pre-standard products early next year as well.

Immersion Center


Caveat emptor: If you buy pre-standard 802.3at gear, get a guarantee in writing that it can be easily upgraded to the final standard via software, and ensure that it's interoperable with the PDs to be powered.

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