Allied Telesis AT-SBx8, Installation Manual

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Chapter 2: Ethernet Line Cards
50
Power over Ethernet on the AT-SBx81GP24 Line Card
This section applies to the AT-SBx81GP24 PoE Line Card. The twisted-
pair ports on the line card support Power over Ethernet (PoE). PoE is a
mechanism by which the ports supply power to network devices over the
twisted pair cables that carry the network traffic. This feature can simplify
network installation and maintenance because it allows you to use the
switch as a central power source for other network devices.
Devices that receive their power over Ethernet cables are called powered
devices (PD), examples of which include 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 AT-SBx81GP24 Line Card automatically determines whether a device
connected to a port is a PD. A PD has a signature resistor or signature
capacitor that the line card can detect over the Ethernet cabling. If the
resistor or capacitor is present, the switch assumes that the device is a
PD.
A port connected to a network node that is not a PD (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.
Powered Device
Classes
The IEEE 802.3af and 802.3at standards define five powered device
classes. The classes are defined by the power requirements of the
powered devices. The classes are shown in Table 13. The AT-
SBx81GP24 Line Card supports all five classes.
Table 13. IEEE802.3af and IEEE802.3at Powered Device Classes
Class Usage
Maximum
Power Output
on the PoE
Port
PD Power
Range
0 Default 15.4W .044W 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
4 Optional 30.0W 12.95W to
25.9W