The ABCs of PoE

According to Daniel Feldman, Technical Chair of the Ethernet Alliance’s PoE subcommittee, the base definition of power over Ethernet (PoE) is, “a technology that allows for the powering of devices through Ethernet cables.” At this time, IEEE 802.3AF is the de facto standard. According to the current standard, 12.95 watts of power can be supplied to a device through the Ethernet cable.

“This means that in theory, you could power any device that uses up to 13 watts of power,” Feldman said.

The IP industry, or more specifically, the VoIP market, has been driving both adoption and interest in PoE. Feldman said devices, such as VoIP phones, network cameras, WiMAX subscriber stations, point-of-sale devices, RFID readers and wireless access points, are all suitable for PoE and are helping prove its viability.

Power sourcing

There are two primary ways to actually harvest the initial power source that is then transmitted through the Ethernet cable. One is back at the Ethernet switch, which would have PoE capabilities, and the other is through midspan power injectors that work off of switches not necessarily designed for PoE.

Feldman said the reason behind the two options is that, “In Greenfield installations where one would need to buy a switch, they would do so and buy one with PoE. In an existing installation, there is not a need for a new switch and it is easier to simply add on a midspan.”

That rationale makes sense, and it also opens the door for more opportunity, as budget crunched customers may not always want to invest in additional, pricey hardware, such as switches. The ability of the Midspan to operate in roughly the same manner makes that an option most customers could easily understand and use.

Why PoE

One of the lingering questions associated with any new or emerging technology is why use it? Feldman explained PoE’s benefits by discussing the top three reasons for its use.

The first and perhaps the most compelling and logical reason is that it is simply more convenient to opt for PoE for low powered devices that fall within the current 13-watt power range. With PoE, one could both power and connect a device through one cable as opposed to having to use two (one for the network connection and another for the power source).

The second is that PoE affords the added luxury of having centralized backup inherently build within its architecture. This is because the primary power source is harvested back at the main power source and filtered out on as needed basis via PoE.

According to Feldman, “That means that IP telephony phones will work almost 99.999 percent of the time. It is also beneficial, since there is not one UPS located near every phone to ensure operation.”

The third reason is location. There are just some instances where running power is not logistically or economically possible. This could include situations such as mounting network cameras on a ceiling, adding an access point to an attic or even placing a WiMAX station on a roof. By being able to operate off of only one physical cable run to do two operations makes installs easier, faster and less expensive.

Drawbacks, there are always a few

As with anything, there are always a few drawbacks that tend to try to offset the benefits, and PoE is no different.

According to Feldman, “The major drawback associated with PoE is power concentration. Because of this, it is important to make sure that the right electrical configuration and enough amperage are available to operate the system.”

In small scale PoE systems, things such as the electrical systems total availability and air conditioning requirements should be relatively OK the way they were originally designed; however, once larger scale PoE is implemented, things begin to change. According to Feldman, when one starts to get involved in large-scale projects, things such as the air conditioning become increasingly relevant as with the higher power dissipation and funneling comes increased heat generation.

The other drawback is common, and it involves added costs. Even though current switches can be adapted by using a midspan and new switches can be bought with PoE capabilities, it is still an extra cost that needs to be considered. However, the convenience alone is sometimes enough to make up the difference as costs continue to come down on PoE equipment.

What the future holds

All and all, Feldman said, “Any device that requires little power is a good candidate for PoE.” The future looks promising for PoE as users continue to adopt emerging technologies and embrace their ease of installation and use abilities. In fact, some are even taking the PoE technology to new heights that are not even centered around what its initial intentions were for. Things such as PoE wall mountable speakers and PoE guitars are now available.

PoE seems to keep evolving, and according to Feldman, initial steps are already underway and the current 802.3AF standard will have an additional high powered version known as 802.3AT. This newer variation will enhance PoE and increase maximum wattage from its current 13 watt maximum to an impressive 25.5 watts. In fact, Feldman even hints at the beginning talks to even further enhance those maximums over time to upwards of 51 watts over time.

Paying attention to technologies, such as PoE, is an amazing way for contractors to keep their finger on the pulse of what drives installations and interest these days. It is no secret that lowering project costs tops customers lists, and because of the basic principles behind PoE, this is yet another option that customers will most likely be talking about for years to come.

STONG-MICHAS, a freelance writer, lives in central Pennsylvania. She can be reached at

About the Author

Jennifer Leah Stong-Michas

Freelance Writer
Jennifer Leah Stong-Michas is a freelance writer who lives in central Pennsylvania.

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