Power over Ethernet Overview
Fixed Switch Configuration Guide 7-3
balance of power available for PoE. When any change is made to the hardware configuration,
power supply status, or redundancy mode, the firmware recalculates the power available for PoE.
On the S-Series, N-Series, and K-Series switches, you can also manually configure the maximum
percentage of PoE power available to the chassis as a percentage of the total installed PoE power
with the set inlinepower available command. (This feature is not configurable on the G-Series.) If
the power needed or requested exceeds the power available, the system will generate a trap to
notify the system manager, if traps are enabled.
The power available for PoE is distributed based on the configured allocation mode, set with the
set inlinepower mode command:
• Automatic mode, in which available power is distributed evenly to PoE-capable modules
based on PoE port count. (This is the default mode.) Any change in available power, due to a
change in power supply status or redundancy mode or to the addition or removal of modules,
will trigger an automatic redistribution of power.
• Manual mode, in which the power budget for each PoE-capable module is manually
configured, using either CLI commands or the MIBs. The sum of the wattage configured for
each module cannot exceed the total power available on the switch for PoE.
The power budget for each PoE-capable module can be configured manually on the G-Series
with the command set inlinepower assign.
The configured wattage assignments are used to calculate each slot’s percentage of total
available power. If the total available PoE power is reduced, a redistribution of available
power will occur, applying the calculated percentages.
When Manual Mode is Configured
When manual distribution mode is configured, if a PoE module is added to the switch, the PoE
power budget for existing modules will not be recalculated. The new module will have a power
budget of zero until it is manually provisioned. Since the sum of the manually provisioned
wattages cannot exceed the total system power available, it may be necessary to adjust existing
budgets to free up power for the new module.
When a PoE module is removed from a switch configured with manual power distribution mode,
the PoE budget for each module will not be recalculated, based on the assumption that the module
removed will be replaced with a new module that should receive the same amount of PoE power.
As noted above, if the total available PoE power is reduced, the power will automatically be
redistributed based on applying the calculated percentages. If an additional PoE supply is
installed, there is no impact on the assigned PoE since specific wattages have been assigned to
each module. Only the “Total Power Detected” value will change. The extra PoE power, however,
is available for further redistribution manually.
Management of PoE Power to PDs
For each PoE-capable module or switch (for the products listed above), you can configure how its
PoE controller makes power available to attached powered devices (PDs). On a per module basis,
you can configure:
• Real-time mode, in which the PoE controller calculates the power needed by a PD based on
the actual power consumption of the attached devices.
Note: This feature is available only on B5, C5, and G-Series fixed switch products.
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