Poe Interface Power Priority; Poe Configuration And Monitoring - Juniper JUNOS OS 10.3 - SOFTWARE Manual

PoE Configuration and Monitoring

Copyright © 2010, Juniper Networks, Inc.
The powered device communicates to the PoE controller which class it belongs to
when it is connected. The PoE controller then allocates to the interface the maximum
power required by the class (see Table 439 on page 3304). It does not allocate power to
an interface until a powered device is connected. Class 0 is the default class for powered
devices that do not provide class information. Class 4 powered devices are supported
only by switches that support IEEE 802.3at (PoE+).
Static mode—In this mode, you specify the maximum power for each PoE interface.
The PoE controller then allocates this amount of power to the interface from its total
budget. For example, if you specify a maximum value of 8.0 W for
controller allocates 8.0 W out of its total power budget for the interface. This amount
is allocated to the interface whether or not a powered device is connected to the
interface or whether the connected powered device uses less power than 8.0 W.
For switches that support IEEE 802.3af (PoE), the maximum power permitted on any
interface is 15.4 W. This wattage guarantees that, after line loss, the powered device
receives 12.95 W, which is the maximum required by 802.3af-compliant powered
devices.
For switches that support IEEE 802.3at (PoE+), the maximum power permitted on
any interface is 30.0 W. This wattage guarantees that, after line loss, the powered
device receives 25.5 W, which is the maximum required by 802.3at-compliant powered
devices.
In both class and static mode, if the power consumption of a powered device exceeds
the maximum power allocated to the interface, power to the interface is turned off.

PoE Interface Power Priority

You can configure a PoE interface to have either a high or low power priority. The power
priority determines which interfaces receive power if PoE power demands are greater
than the PoE power budget. If the total power allocated for all interfaces exceeds the
switch budget, the lower priority interfaces are turned off and the power allocated to
those interfaces drops to 0. Thus you should set interfaces that connect powered devices
such as security cameras and emergency phones to high priority.
Among PoE interfaces that have the same assigned priority, power priority is determined
by the port number, with lower-numbered ports having higher priority.
The factory default configuration enables PoE on switches that support PoE. By default,
the power management mode is class, and the power priority of all interfaces is low.
If the default configuration meets your needs, you do not need to configure PoE before
you connect powered devices to the switch.
To monitor the powered devices and to manage PoE power consumption, you can use
the CLI or J-Web interface to display the current power consumption of the PoE ports.
You can also enable the monitoring of power consumption on a port over time and then
view the collected records using the CLI or the J-Web interface.
Chapter 114: Power over Ethernet (PoE)—Overview
ge-/0/0/3 , the PoE
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