Seven months ago in this space, I handed out some facts and opinions about the technology behind, and practical uses for, Power over Ethernet-PoE (see “Before you harness the power, make sure you understand its limits,” February 2005, page 6). Since then, I have learned more about the technology and its maturation process, and I thought it only fair to share that information with you now.
This column isn’t so much an “I stand corrected,” (have you ever known me to admit I was wrong?) as it is an, “I stand updated.” And I’d like you to be updated as well.
In February, I stated: Midspan PoE devices, such as PoE-enabled patch panels and standalone power-sourcing equipment, use the spare pairs of your Ethernet cabling. If you are running 1000Base-T over all four pairs of your cabling system, then you have no spare pairs and, therefore, cannot use midspan PoE technology.
Additionally, I stated: Approximately 13 watts of power are available to each powered device. That’s not enough power to support equipment such as laptops or printers. And now the FUD (fear, uncertainty, and doubt) campaigns have begun about whether that’s enough power to allow full functionality of some of the devices commonly associated with PoE-particularly point/tilt/zoom cameras.
Recently, I found out that efforts are underway, and from what I understand are progressing, to address both of those issues with PoE technology. The 802.3 Working Group of the Institute of Electrical and Electronics Engineers (IEEE) is dubbing the technology “PoE Plus.” Among the forthcoming anticipated characteristics of PoE Plus are four-pair transmission (i.e., transmission over pairs in use) and the capability to transmit 30 watts of power to each powered device.
When IEEE 802.3 put out a call-for-interest for PoE Plus, it heralded the original technology as “a successful enhancement to the 802.3 standard,” and even called it “the preferred power source for numerous network devices, most notably WLAN access points, IP telephones, and networked security cameras.”
One reason for considering PoE Plus, the call-for-interest stated, was that “the market is changing rapidly and some of the market needs are not easily addressed by the present standard. Consequently, companies are releasing nonstandard, noninteroperable devices to address market needs.” Reports indicate that 22 companies supported the PoE Plus call for interest, including at least five “household names” within the cabling industry. That number convinces me there’s enough support within this industry to consider the initiative serious.
Before any IEEE group progresses to the point of drafting a standard, the technology under development has to meet several criteria, including a realistic chance of market success, as well as economic and technical feasibility. One early presentation within the working group cited a wide array of applications that PoE Plus could serve. That presentation also outlined some applications that are above the 13-watt limit set in the original PoE specs. Among those greater-than-13-watt applications are point/tilt/zoom IP cameras (which the presenter listed as consuming between 20 and 40 watts), video IP phones in the 20- to 30-watt range, and laptop computers, which may start as low as 40 watts and consume as much as 70.
From early indications, it looks like there’s still a lot to sort out with PoE Plus, but it seems clear to me the group is at least paying attention to common applications, with the hope of making PoE Plus a nearly universal powering option.
Other presentations to the group discussed the possibility of four-pair power transmission over twisted-pair cabling. Believe me when I say they’re a bit more difficult to unravel than the presentations explaining market acceptance. And feel free to take a look at them yourself, and then fill me in on what all the circles and arrows mean.
To me, they mean the debate goes on. So, in my New Hampshire country-bumpkin style, I’ll assume (and pass on to you) that the idea of sending PoE down active pairs of a twisted-pair cable is not yet a “done deal” with the IEEE.
Certainly, progress is being made to position PoE as a technology of choice for business consumers. And as always, we’ll aim to keep you updated, both in print and online, of this and other technologies that will influence decisions you make each day.
PATRICK McLAUGHLIN
Chief Editor
[email protected]
