H3C Technologies H3C S5120 Series Switches - Manual (Page 719)

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z 19 watts guard band is reserved for each PoE interface on the device to prevent a PD from being
powered off because of a sudden increase of the PD power. When the remaining power of the
PSE is lower than 19 watts and no priority is configured for the PoE interface, the PSE does not
supply power to the new PD; when the remaining power of the PSE is lower than 19 watts, but
priority is configured for the PoE interface, the interface with a higher priority can preempt the
power of the interface with a lower priority to ensure the normal working of the higher priority
interface.
z If the sudden increase of the PD power results in PSE power overload, power supply to the PD on
the PoE interface with a lower priority will be stopped to ensure the power supply to the PD with a
higher priority.
If the guaranteed remaining PSE power (the maximum PSE power minus the power allocated to the
critical PoE interface, regardless of whether PoE is enabled for the PoE interface) is lower than the
maximum power of the PoE interface, you will fail to set the priority of the PoE interface to critical.
Otherwise, you can succeed in setting the priority to critical, and this PoE interface will preempt the
power of other PoE interfaces with a lower priority level. In the latter case, the PoE interfaces whose
power is preempted will be powered off, but their configurations will remain unchanged. When you
change the priority of a PoE interface from critical to a lower level, the PDs connecting to other PoE
interfaces will have an opportunity of being powered.
Configuration prerequisites
Enable PoE for PoE interfaces.
Configuration procedure
Follow these steps to configure PoE interface power management:
To do… Use the command… Remarks
Enter system view system-view —
Enter PoE interface view
interface interface-type
interface-number
—
Configure the power supply
priority for a PoE interface
poe priority { critical | high | low }
Optional
low by default.
Configuring the PoE Monitoring Function
After the PoE monitoring function is enabled, the system monitors the parameter values related to PoE
power supply, PSE, PD, and device temperature in real time. When a specific value exceeds the
limited range, the system will automatically take some measures to protect itself.