Allied Telesis AT-GS950/8POE - Manual (Page 22)

Chapter 1: Overview
22
Power over Ethernet
The four of the twisted pair ports on the AT-GS950/8POE switch feature
Power over Ethernet (PoE) which 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 receives both network traffic and
power over the same twisted pair cable.
There are several advantages that the PoE feature of the AT-GS950/
8POE switch adds to the installation and maintenance of your network.
The switch acts as the central power source for your powered devices.
Adding an uninterruptible power source (UPS) to the switch, increases the
protection to the switch from possible power source problems and to all of
the powered devices connected to the switch. The PoE feature 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 making sure 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 where they are
needed without being concerned 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 detects 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 and, simultaneously, furnishing standard 10/
100 Mbps Ethernet functionality. A PoE port that is 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.