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Power over Ethernet on the AT-SBx31GP24 Line Card
Powered Device
Classes
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This section applies only to the AT-SBx31GP24 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-SBx31GP24 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.
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 3. The AT-SBx31GP24
Line Card supports all five classes.
Table 3. IEEE802.3af and IEEE802.3at Powered Device Classes
Class
0
1
2
3
4
Maximum
Power Output
Usage
on the PoE
Port
Default
15.4W
Optional
4.0W
Optional
7.0W
Optional
15.4W
Optional
30.0W
SwitchBlade x3112 Installation Guide
PD Power
Range
0.44W to
12.95W
0.44W to 3.84W
3.84W to 6.49W
6.49W to
12.95W
12.95W to
25.9W
39
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