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Setting The Port
Use the Administration > PoE (Configure Interface) page to set the maximum
power provided to a port.
PoE Power Budget
Command Usage
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This switch supports both the IEEE 802.3af PoE and IEEE 802.3at-2009 PoE Plus
standards. To ensure that the correct power is supplied to powered devices
(PD) compliant with these standards, the first detection pulse from the switch is
based on 802.3af to which the 802.3af PDs will respond normally. It then sends
a second PoE Plus pulse that causes an 802.3at PD to respond as a Class 4
device and draw Class 4 current. Afterwards, the switch exchanges information
with the PD such as duty-cycle, peak and average power needs.
All the RJ-45 ports support both the IEEE 802.3af and IEEE 802.3at standards.
The total PoE power delivered by all ports cannot exceed the maximum power
budget of 390W. This means that up to 11 ports can supply a maximum 34.2W
of power simultaneously to connected devices (802.3at), or all 12/24 ports can
supply up to 15.4W (802.3af ).
If the power demand from devices connected to all switch ports exceeds the
power budget as determined during bootup, the port power priority settings
are used to control the supplied power. For example:
If a device is connected to a low-priority port and causes the switch to
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exceed its budget, power to this port is not turned on.
If a device is connected to a critical or high-priority port and would cause
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the switch to exceed its power budget, power is provided to the port only if
the switch can drop power to one or more lower-priority ports and thereby
remain within its overall budget.
Power will be dropped from low-priority ports in sequence starting from
port number 1.
If priority is not set for any ports, power is denied in reverse sequence,
starting from Port 12/24.
If sufficient power cannot be freed up for a critical or high-priority port by
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turning off power to lower-priority ports, power will not be supplied to the
newly connected device.
If priority is not set for any ports, and there is not sufficient power to supply all
of the ports, port priority defaults to Port 1, Port 2, Port 3 ... Port 24, with
available power being supplied in that sequence.
If a device is connected to a switch port after bootup and the switch detects
that it requires more than the power budget set for the port or for the overall
switch, no power is supplied to the device regardless of its priority setting.
– 383 –
Chapter 13
| Basic Administration Protocols
Power over Ethernet
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