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PoE Priority Example
A 48-port device is supplying a total of 375 watts.
The administrator configures all ports to allocate up to 30 watts each. This results in 48 times 30
ports equaling 1440 watts, which is too much. The device cannot provide enough power to each
port, so it provides power according to the priority.The administrator sets the priority for each
port, allocating how much power it can be given.
These priorities are entered in the PoE Port Limit Mode or Class Limit Power Mode pages.
PoE Configuration Considerations
There are two factors to consider in PoE configuration:
•
The amount of power that the PSE can supply
•
The amount of power that the PD is attempting to consume
You can decide the following:
•
Maximum power a PSE is allowed to supply to a PD
•
POE mode—To change the mode from Class Power Limit to Port Limit, and vice versa,
during device operation. The power values per port that were configured for the Port Limit
mode are retained.
Note
—
Changing the mode from Class Limit to Port limit, and vice versa, when the device
is operational forces the Powered Device to reboot.
•
Maximum port limit allowed as a per-port numerical limit in mW (Port Limit mode).
The PoE-specific hardware automatically detects the PD class and its power limit according to
the class of the device connected to each specific port (Class Limit mode).
If at any time during the connectivity an attached PD requires more power from the device than
the configured allocation allows (no matter if the device is in Class Limit or Port Limit mode), the
device maintains the up/down status of the PoE port link, turns off power delivery to the PoE port,
and logs the reason for turning off power.
Caution
—
Consider the following when connecting switches capable of supplying PoE.
o
The PoE model of the device is PSE (Power Sourcing Equipment) that is capable of
supplying DC power to attaching PD (Powered Devices). These devices include
VoIP phones, IP cameras, and wireless access points.
o
Even though the PoE switches are PSE, and as such should be powered by AC,
they could be powered up as a legacy PD by another PSE due to false detection.
When this happens, the PoE device may not operate properly and may not be able
to properly supply power to its attaching PDs.