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Catalyst 3750-E and 3560-E Switch Software Configuration Guide
OL-9775-08
Chapter 12 Configuring Interface Characteristics
Interface Types
In Cisco IOS Release 12.2(40)SE and earlier, each 10/100/1000 PoE port provides up to 15.4 W of power to
the device. Cisco IOS Release 12.2(44)SE and later supports enhanced PoE. Enhanced PoE should be con-
figured on a port to power a device requiring up to 20 W of power, such as the Cisco AP1250 wireless access
point.
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.
This section has this PoE information:
•
Supported Protocols and Standards, page 12-7
•
Powered-Device Detection and Initial Power Allocation, page 12-7
•
Power Management Modes, page 12-9
•
Power Monitoring and Power Policing, page 12-10
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 802.11n (pre-draft standard)—This standard allows you to increase the power on an enhanced
PoE port up to 20W.
Powered-Device Detection and Initial Power Allocation
The switch detects a Cisco pre-standard or an IEEE-compliant powered device when the PoE-capable
port is in the no-shutdown state, PoE is enabled (the default), and the connected device is not being
powered by an AC adaptor.
After device detection, the switch determines the device power requirements based on its type:
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