Cisco SF220-24 Administration Manual page 127

Power over Ethernet
PoE on the Switch
Cisco 220 Series Smart Switches Administration Guide Release 1.1.0.x
PoE can be used in any enterprise network that deploys relatively low-powered
devices connected to the Ethernet LAN, such as:
• IP phones
• Wireless access points
• IP gateways
• Audio and video remote monitoring devices
PoE Operation
PoE implements in the following stages:
• Detection—Sends special pulses on the copper cable. When a PoE device
is located at the other end, that device responds to these pulses.
• Classification—Negotiation between the PSE and the PD commences
after the Detection stage. During negotiation, the PD specifies its class,
which is the amount of maximum power that the PD consumes.
• Power Consumption—After the classification stage completes, the PSE
provides power to the powered device (PD). The PD without classification
support will be assumed to be class 0 (the maximum). If a PD tries to
consume more power than permitted by the standard, the PSE stops
supplying power to the port.
PoE supports two modes:
• Port Limit—The maximum power that the switch agrees to supply is limited
to the value that the system administrator configures, regardless of the
classification result.
• Class Limit—The maximum power that the switch agrees to supply is
determined by the results of the classification stage. This means that it is
set as per the client's request.
PoE Configuration Considerations
There are two factors to consider in the PoE feature:
• The amount of power that the PSE can supply
• The amount of power that the PD is actually attempting to consume
You can decide the following:
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