in Hardware, Telephony

the pros and cons of Power over Ethernet

Spurred on by a recent thread on the TAUG mailing list, I’ve been thinking about the cost vs. benefits of Power over Ethernet (PoE). PoE is a way to use the extra 4 wires in 10/100/1000-baseT Ethernet wiring for powering devices. The obvious application is to power IP telephones. Cisco has been doing this for a while using a proprietary solution which is similar to the PoE standard, IEEE 802.3af, which defines a protocol for detecting whether a device (or PD) is capable of receiving power prior to applying it, so that non-PDs don’t get fried by sending 48VDC down the wire. The protocol also determines how much current the PD will draw, and classifies the PD into a device class. All of this is well-described by this Wikipedia article.

There are two main advantages to using PoE, so far as I can see:

  1. No need to get a separate power brick for each device
  2. PDs can be centrally powered from a UPS in case of mains failure

The main con is the added cost, since you now need to purchase a PoE-enabled switch (which will then draw quite a bit of power, as it needs to power the devices).

What kind of cost are we talking about here?

  1. HP Procurve 2650 48-port switch (non-powered): USD $812.99
  2. HP Procurve 2650-PWR 48-port switch (PoE): USD $3,312.99

This works out to about USD $50/port, which I still think is a bit high. But maybe once the cost drops to around USD $25/port, it will be worth it.

Originally I was going to mention that purchasing PoE power injectors is another solution. A power injector has two Ethernet ports and a power brick attached to it; one of the Ethernet ports is an input from the regular non-powered network, and the other is a PoE output port to your PD. But I did some digging and find that the cost of a power injector is greater than USD $50, so I suppose this would only be feasible for a small deployment.

Step back for a moment and you realize that the cost of implementing the logic for PoE is far, far less than USD $50/port. The manufacturers are clearly just capitalizing on the fact that this is “new” technology and making a huge profit on it. As such I predict that there will definitely be wiggle room on the price in the future which will make PoE deployments more cost-effective.

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  1. I was actually thinking about POE today.. we were playing around with some network security cams that had ethernet interfaces, but used a standard power brick for juice. Would have been alot easier just to plug in and get everything from the ethernet port, and give us alot more flexibility in locating the cam in the office. Depending on how far the trickle down goes, we might see this in consumer electronics soon?

  2. If someone like Linksys can get their PoE switch prices down to a reasonable level — and I mean the PoE switches with a small (< eight) number of ports — then I think there would be some adoption in the consumer market. I can just see the proliferation of all kinds of PoE junk, though, just like the USB-powered junk you can get at Active Surplus — PoE-powered coffee warmers, thermal blankets, LED reading lamps… 🙂

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    See you!
    Your, Raiul Baztepo