Allied Telesis AT-S81 - Manual (Page 104)

Chapter 8: Power Over Ethernet
104 Section I: Using the Menus Interface
PoE Overview
The twisted pair ports on the AT-8000/8POE Fast Ethernet 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.
Note
The uplink ports (9 and 9R) do not provide PoE.
Power Budgeting
A port on the switch connected to a powered device can supply up to 15.4
watts of power to the device, 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.
The AT-8000/8POE Fast Ethernet Switch can provide up to a total of 95
watts (W) of PoE power and a maximum of 15.4 W per port.
Port
Prioritization for
Power Allocation
The AT-S81 management software also allows you to prioritize the ports
in the event that the powered devices require more power than the switch
can deliver. This feature ensures that the most important powered devices
connected to the switch are guaranteed to have power.
If the powered devices connected to the switch require more power than
the switch is capable of delivering, the switch denies power to some ports
based on a system called port prioritization. You can use this system to
ensure that powered devices that are critical to your network are given
preferential access to the available power.