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Monday, October 20, 2014

Power over Ethernet (PoE) Explained

http://www.gowifi.co.nz/power-over-ethernet-poe.html

When it comes to Power over Ethernet, there a couple of different terms that we need to be familiar 
with, and what those different terms mean. 
Power over Ethernet is a method of supplying power over network cables to power end devices such as desk phones or access points.

There are 2 standards when it comes to PoE:
802.3af:
  • This is referred to as PoE
  • The maximum amount of power it can provide is 15.4 watts
  • This will power most phones and access points
  • Compatible with gigabit Ethernet
  • Generally 48 volts, but is allowable to be anywhere from 44 to 57 volts.
802.3at:
  • This is referred to as PoE+
  • The maximum amount of power it can provide is 25.5 Watts.
  • Is backwards compatible with 802.3af
  • Generally 48 volts, but is allowable to be anywhere from 44 to 57 volts.
By default, ports enabled with 802.3af and 802.3at do not send power all the time, there is a negation that takes place with the end device before it sends power down the Ethernet cable, thus saving your non-PoE device from being powered and blowing up your laptops Ethernet port. The end device has to be 802.3af or at compliant for power to be sent down.

There is also a 3rd way of delivering Power over Ethernet and that is passively.
Passive PoE means that there is a constant feed over power over the the Ethernet wires, and it is not negotiate like 802.3at and af do. Because Passive PoE does not have any active components, this means that it is not defined by a IEEE standard.
This means if you plug in your device to a passive power supply, it will likely blow the Ethernet port up. 
  • Passive PoE can come in any voltage, usually anywhere from 12-57 Volts
  • Devices that are 802.3at & 802.3at can be powered by Passive PoE providing that the voltages & watts being delivered are correct

Click here to see what range of PoE Power supplys Go Wireless can offer you

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