Allied Telesis AT-S88 - Manual (Page 42)

Chapter 4: Power over Ethernet
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PoE Overview
The twisted pair ports on the AT-FS750/24POE Fast Ethernet Smart
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, webcams, and even other Ethernet switches. An example
of the latter is the unmanaged AT-FS705PD Ethernet switch from Allied
Telesis. A powered device connected to a port on the switch will receive
both network traffic and power over the same twisted pair cable.
The switch automatically determines whether a device connected to a port
is a powered device or not. 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.
Power Budgeting
The AT-FS750/24POE Fast Ethernet Smart switch provides a maximum
of 15.4 W of power per port on six of the twelve ports for a total power
consumption of 95 W, 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.
You can allocate this power budget in one of two ways:
ˆ Maximum power (15.4 W) on each of 6 of the 12 PoE ports (Class 3)
ˆ Up to 7.3 W on all 12 PoE ports (Class 2)
Using the AT-S88 management software, you can enable or disable PoE
on a per-port basis and change the amount of power a port can receive.
The AT-S88 management software also allows you to prioritize the ports
in the event that there is not enough PoE power for all the powered
devices. This feature can help ensure that the most important powered
devices connected to the switch are guaranteed to have power.
The default setting for PoE on the switch is disabled at the port level.
Implementation A standard Ethernet twisted pair cable contains four pairs of strands for a
total of eight strands. 10/100 Mbps network traffic requires only four