3Com 2928 User Guide - Page 502

Item Power Priority Description Set the power supply priority for a PoE port. The priority levels of a PoE port include low, high, and critical in ascending order. z When the PoE power is insufficient, power is first supplied to PoE ports with a higher priority level. z When the PSE power is overloaded, the PoE port with a lower priority is first disconnected to guarantee the power supply to the PD with a higher priority. z If you set the priority of a PoE port to critical, the system compares the guaranteed remaining PSE power (the maximum PSE power minus the maximum power allocated to the existing critical PoE port, regardless of whether PoE is enabled for the PoE port) with the maximum power of this PoE port. If the former is greater than the latter, you can succeed in setting the priority to critical, and this PoE port will preempt the power of other PoE ports with a lower priority level; otherwise, you will fail to set the PoE port to critical. In the former case, the PoE ports whose power is preempted will be powered off, but their configurations will remain unchanged. When you change the priority of a PoE port from critical to a lower level, the PDs connecting to other PoE ports will have an opportunity of being powered. By default, the power priority of a PoE port is low. z 19 watts guard band is reserved for each PoE port 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, the port with a higher priority can preempt the power of the port with a lower priority to ensure the normal working of the higher priority port. 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. Displaying Information About PSE and PoE Ports Select PoE > PoE from the navigation tree to enter the page of the Summary tab. The upper part of the page displays the PSE summary; Click a port on the chassis front panel, the configuration and power information will be displayed in the lower part of the page, as shown in Figure 1-3. 1-4