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Chapter 1: Overview
Power Over Ethernet
PoE Standards
Power Budget
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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 to
make it easier to install a network. The placement of network devices is
often limited by whether there are power sources nearby. This often limits
equipment placement or requires the added time and cost of having
additional electrical sources installed. But with PoE, you can install PoE-
compatible devices wherever they are needed without having to worry
about whether there are power sources nearby.
A device that provides PoE to other network devices is referred to as
power sourcing equipment (PSE). The PoE switches act as PSE units by
adding DC power to the network cable, thus functioning as a central power
source for other network devices.
Devices that receive their power from a PSE are called powered devices
(PD). Examples include wireless access points, IP telephones, 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.
The AT-FS980M/9PS, AT-FS980M/18PS, AT-FS980M/28PS, AT-
FS980M/28DP, and AT-FS980M/52PS switches support these PoE
standards:
PoE (IEEE 802.3af): This standard provides up to 15.4 watts at the
switch port to support powered devices that require up to 12.95
watts.
PoE+ (IEEE 802.3at): This standard provides up to 30.0 watts at
the switch port to support powered devices that require up to 25.5
watts.
The power budget is the maximum amount of power the switch can
provide at one time to the powered devices. The AT-FS980M/9PS,
AT-FS980M/18PS, AT-FS980M/28PS, AT-FS980M/28DP, and
AT-FS980M/52PS switches support both Power over Ethernet (PoE) and
Power over Ethernet Plus (PoE+) on 10/100Mbps twisted pair ports.
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