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Power-over-Ethernet
PoE on the Switch
Cisco 220 Series Smart Plus Switches Administration Guide Release 1.0.0.x
PoE Operation
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
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:
•
During device operation, to change the mode from Class Limit to Port Limit
and vice versa. The power values per port that were configured for the Port
Limit mode are retained.
Changing the mode from Class Limit to Port limit and vice versa when
NOTE
the switch is operational forces the PD to be reconnected.
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