Allied Telesis AT-S63 - Manual (Page 191)

AT-S63 Management Software Menus User’s Guide
Section II: Advanced Operations 191
Overview
Power over Ethernet (PoE) is a mechanism for supplying power to network
devices over the same twisted pair cables that carry the network traffic.
This feature, defined in the IEEE 802.3af standard, can make the
installation and maintenance of a network easier.
The device that provides the power, in this case the AT-9424T/POE
Switch, acts as a central power source for other network devices. A device
that receives its power from the central power source is called a powered
device. Examples include wireless access points, IP telephones,
webcams, and even other Ethernet switches, such as the unmanaged
AT-FS705PD Ethernet switch from Allied Telesis.
One of the advantages that the PoE feature offers is that it can simplify the
installation of your network. The selection of a location for a network
device is often limited by whether there is a power source 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.
This feature can also add to the reliability of a network. Since the switch
acts as the central power source for your powered devices, adding a
redundant power supply (RPS) or uninterruptible power source (UPS) to
the device increases the protection not just to the switch from possible
power source problems but also to all of the powered devices connected
to it.
The switch automatically determines whether or not the devices connected
to the ports are powered devices. 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 IEEE 802.3af standard defines two methods for implementing PoE
over twisted pair cabling. One method uses the same strands that carry
the network traffic and the other the spare strands. The ports on the
AT-9424T/POE Switch deliver the power using strands 1, 2, 3, and 6 of the
twisted pair cable. These are the same strands that carry the Ethernet
traffic. This corresponds to Alternative A in the IEEE 802.3af standard.