Allied Telesis AT 8000/8POE - Manual (Page 23)

AT-8000/8POE Layer 2 Fast Ethernet Switch Installation Guide
23
Power over Ethernet
The twisted pair ports on the AT-8000/8POE Fast Ethernet Switch feature
Power over Ethernet (PoE). PoE is a mechanism for supplying power to
network devices over the same twisted pair cables used to carry network
traffic. This feature can simplify network installation and maintenance by
allowing you to use the switch as a central power source for other network
devices.
A device that receives its power over an Ethernet cable is called a
powered device. Examples of such devices can be wireless access points,
IP telephones, web cams, and even other Ethernet switches. A powered
device connected to a port on the switch will receive both network traffic
and power over the same twisted pair cable.
There are several advantages that the PoE feature of the AT-8000/8POE
Fast Ethernet Switch adds to the installation and maintenance of your
network. First, because the switch acts as the central power source for
your powered devices, adding an uninterruptible power source (UPS) to
the switch increases the protection not just to the switch itself from
possible power source problems but also to all of the powered devices
connected to it. This can increase the reliability of your network by
minimizing the impact to network operations from a power failure.
PoE can also simplify the installation of your network. A frequent issue in
selecting a location for a network device is whether there is a power
source nearby. This often limits equipment placement or requires the
added cost and time of having additional electrical sources installed. With
PoE, you can install PoE-compatible network equipment wherever they
are needed without having to worry about whether they are near a power
source.
The switch automatically determines whether or not a device connected to
a port is a powered device. A powered device has a signature resistor or
signature capacitor that the switch can detect over the Ethernet cabling. If
the resistor or capacitor is present, the switch assumes that the device is a
powered device.
A port on the switch connected to a powered device can supply up to 15.4
watts of power to the device, while at the same time furnishing standard
10/100 Mbps Ethernet functionality. A port connected to a network node
that is not a powered device (that is, a device that receives its power from
another power source) functions as a regular Ethernet port, without PoE.
The PoE feature remains enabled on the port but no power is delivered to
the device.