Allied Telesis X8106 Power over Ethernet on the AT-SBx81GP24 Line Card, Powered Device Classes

SwitchBlade x8106 Chassis Switch Installation Guide

Power over Ethernet on the AT-SBx81GP24 Line Card

Powered Device Classes

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.

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-SBx81GP24 Line Card supports all five classes.

Table 3. IEEE802.3af and IEEE802.3at Powered Device Classes

		Maximum
Class	Usage	Power Output	PD Power
		on the PoE	Range
		Port
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

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