Allied Telesis AT-9000 Series - Manual (Page 156)

Chapter 14: Power Over Ethernet (PoE)
156
Overview
The AT-9000/12POE and AT-9000/28POE switches feature PoE on the
10/100/1000Base-Tx ports. PoE is used to supply power to network
devices over the same twisted-pair cables that carry the network traffic.
The main advantage of PoE is that it can make installing a network easier.
The selection of a location for a network device is often limited by whether
there is a power source nearby. This constraint limits equipment
placement or requires the added time and cost of having additional
electrical sources installed. However, with PoE, you can install PoE
compatible devices wherever they are needed without having to worry
about whether there is a power source nearby.
Power Sourcing
Equipment (PSE)
A device that provides PoE to other host devices is called power sourcing
equipment (PSE). The AT-9000/12POE and AT-9000/28POE switches act
as PSE units by adding DC power to the network cable, thus functioning
as a central power source for other host devices.
Powered Device
(PD)
A device that receives power from a PSE device is called a powered
device (PD). Examples include wireless access points, IP phones,
webcams, and even other Ethernet switches.
The switch automatically determines whether or not a device connected to
a port is a powered device. Ports that are connected to network nodes that
are not powered devices (that is, devices that receive their power from
another power source) function as regular Ethernet ports, without PoE.
The PoE feature remains activated on the ports, but no power is delivered
to the devices.
PD Classes PDs are grouped into five classes. The classes are based on the amount
of power that PDs require. The AT-9000/12POE and AT-9000/28POE
switches support all five classes listed in Table 2.
Table 2. IEEE Powered Device Classes
Class
Maximum Power Output
from a Switch Port
Power Ranges of the PDs
0 15.4W 0.44W to 12.95W
1 4.0W 0.44W to 3.84W
2 7.0W 3.84W to 6.49W
3 15.4W 6.49W to 12.95W
4 30.0W 12.95W to 25.5W