Tuesday, 20 August 2013

PoE has its day

Power over Ethernet has been around quite a while, and there are now numerous devices that can be powered by PoE. This means powering the device over the Ethernet cable and not needing a separate power adapter for the device.

Notably this is very useful for VoIP phones, like the SNOM 300, and for access points for WiFi. Both of these can end up being put in places where power is a pain to arrange. Phones because of yet another power socket and lead on a desk, and APs because they end up high up and above false ceilings and so on. You want to be able to put an AP where it works best, not where it is in range of a power lead. PoE works over 100m cat5 cable.

Up until now we have used very little PoE stuff, largely because PoE switches are expensive. At home I want fanless switches to keep noise down.

I was quite pleased to see that you can now get an 8 port gigabit unmanaged fanless switch with 4 ports PoE for under £100! It seems netgear, dlink and tplink do them. These are not necessarily the best names in switches, but for home use and for such a low price, they are well worth considering.

The fact you can power 4 devices of one of these switches also saves having power adapters and extension leads. Reduced mess and leads always goes down well with the wife :-)

It has allowed me to place the home AP in a sensible place, high up on ground floor, where I happened to have network already, but no power.

10 comments:

  1. We use the 8 powered ports version for slightly more: http://www.amazon.co.uk/gp/product/B003GOFIBS

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  2. I actually bought the D-Link switch purely as an "experimental" purchase and am very happy with it. I will be using more PoE kit, and more gigabit kit, in the future.

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  3. The only problem with those little POE switches is they often have a fairly low total power budget, So don't expect to be able to pull the full 802.3af limit on each port.

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  4. Replies
    1. Best Guess is it's a satellite/cable connection for a TV

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    2. Yeh, wired whole house when I moved in with Cat5 and sat/TV cabling...

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  5. We've got an Atlas monitoring device from RIPE which takes its power over USB: ideal as our router has a USB socket... Yes, it's two sockets needed (one for ethernet one for USB), but with USB being such as "standard" would it be more beneficial for routers/devices to use that for power instead of PoE?

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    1. The argument is that for a networking device you're already running the networking cable, so even usb is extra so what's there already

      The only argument I can think of where USB power is preferable to PoE is when your device is 802.11 only, surely?

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  6. Apart from the additional cable the other downsides to USB are the amount of power it provides and the voltage it uses. USB uses 5V and can provide 2.5W (USB2) or 4.5W (USB3). 802.11af uses 44V and can provide 15.4W. Things like Access Points will want the higher power levels of PoE. Also for longer cable runs you would need thicker wires to carry the higher current used by USB so Cat5e cable may not be suitable.

    The advantage that USB power has is that it's cheaper to implement in the device. That saving would probably be outweighed by the additional cost of running the cable to power it.

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    Replies
    1. Don't forget that 802.3at (aka PoE+) goes from 15.4W to 25.5W - that's over 5 times the power of USB 3.0, and ten times the power of USB 2.0.

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