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Information about PoE

Power over Ethernet Ports

A PoE-capable switch port automatically supplies power to one of these connected devices if the switch senses

that there is no power on the circuit:

•

a Cisco pre-standard powered device (such as a Cisco IP Phone or a Cisco Aironet Access Point)

•

an IEEE 802.3af-compliant powered device

•

an IEEE 802.3at-compliant powered device

A powered device can receive redundant power when it is connected to a PoE switch port and to an AC power

source. The device does not receive redundant power when it is only connected to the PoE port.

After the switch detects a powered device, the switch determines the device power requirements and then

grants or denies power to the device. The switch can also sense the real-time power consumption of the device

by monitoring and policing the power usage.

Supported Protocols and Standards

The switch uses these protocols and standards to support PoE:

• CDP with power consumption—The powered device notifies the switch of the amount of power it is

consuming. The switch does not reply to the power-consumption messages. The switch can only supply

power to or remove power from the PoE port.

• Cisco intelligent power management—The powered device and the switch negotiate through

power-negotiation CDP messages for an agreed-upon power-consumption level. The negotiation allows

a high-power Cisco powered device, which consumes more than 7 W, to operate at its highest power

mode. The powered device first boots up in low-power mode, consumes less than 7 W, and negotiates

to obtain enough power to operate in high-power mode. The device changes to high-power mode only

when it receives confirmation from the switch.

High-power devices can operate in low-power mode on switches that do not support power-negotiation

CDP.

Cisco intelligent power management is backward-compatible with CDP with power consumption; the

switch responds according to the CDP message that it receives. CDP is not supported on third-party

powered devices; therefore, the switch uses the IEEE classification to determine the power usage of the

device.

• IEEE 802.3af—The major features of this standard are powered-device discovery, power administration,

disconnect detection, and optional powered-device power classification. For more information, see the

standard.

• IEEE 802.3at—The PoE+ standard increases the maximum power that can be drawn by a powered

device from 15.4 W per port to 30 W per port.

Catalyst 2960-X Switch Interface and Hardware Component Configuration Guide, Cisco IOS Release 15.0(2)EX

76 OL-29034-01

Configuring PoE

Information about PoE

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Cisco Systems WSC2960X48TDL Bedienungsanleitung Seite 88