Allied Telesis AT-FS708/POE - Manual (Page 22)

Chapter 1: Overview
22
Power over Ethernet
The twisted-pair ports on the AT-FS708/POE 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 (PD). Examples of such devices can be wireless access
points, IP telephones, web cams, and even other Ethernet switches. A PD
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-FS708/POE
Fast Ethernet switch adds to the installation and maintenance of your
network. First, because the switch acts as the central power source for
your PDs, 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 PDs 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 PD. A PD 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 PD.