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14
Power over Ethernet
The four twisted-pair ports on the AT-FS708LE/PoE 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.
Powered Device
(PD)
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 receives both network traffic and power
over the same twisted-pair cable.
The switch automatically determines whether or not a device connected to
a port is a PD. A PD has a resistor or 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.
Power Budgeting
The AT-FS708LE/PoE switch provides a maximum power of 15.4 W per
port on four ports for a total power consumption of 30 W, while furnishing
standard 10/100 Mbps Ethernet functionality. The switch supports four
class 2 PDs on four PoE ports or two class 3 PDs on two PoE ports. The
IEEE 802.3af Class power level table is shown in Table 2.
The PoE port that is connected to a non-PD, a device receiving its power
from another power source, functions as a regular Ethernet port. The PoE
feature remains enabled on the port but no power is delivered to the
device.
Table 2. IEEE 802.3af Class vs. Power Levels
Class
Usage
Maximum Power
Levels Output at
the PoE Port
Range of Power
Levels Available
at the PD Inpu
t
0
Default
15.4W
0.44W to 12.95W
1
Optional
4.0W
0.44W to 3.84W
2
Optional
7.0W
3.84W to 6.49W
3
Optional
15.4W
6.49W to 12.95W
