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24-Port Gigabit (Hi-Power) PoE+ Ethernet Smart Managed Pro Switch with 2 SFP Ports
Configure System Information User Manual90
It is important to note that although a device is listed as an 802.3at (PoE+) powered or
802.3af (PoE) powered device, it might not require the maximum power limit that is specified.
Many devices require less power, allowing all PoE+ ports to be active simultaneously, when
the devices correctly report their PoE class to the switch.
Device class power requirements
PoE and PoE+ use Ethernet cables to supply power to PoE-capable devices on the network,
such as WiFi access points, IP cameras, VoIP phones, and switches. The switch is compliant
with the IEEE 802.3at standard (PoE+) and backward compatible with the IEEE 802.3af
standard (PoE). The switch can pass power through to any powered device (PD) that
supports these standards. PoE and PoE+ let you power such devices without the need for a
separate power supply.
The switch supports a Plug-and-Play process by which it detects the type of device that is
connected to one of its PoE+ ports and whether that device needs power and how much so
that the switch can provide the correct power to the device.
During the Plug-and-Play process, the connected device can provide its Class response to
the switch in many ways, depending on how the vendor programmed the device.
The following table shows the device classes for PoE+ devices adhering
to the
IEEE 802.3at
standard. The device classes for PoE devices adhering to the IEEE 802.3af standard are
identical with the exception that Device Class 4 is not supported.
Table 15. PoE and PoE+ device class power allocation
Device
Class
Standard Range of Power Deliv-
ered to the Powered
Device
Minimum Output at
PoE Switch Port (Mini-
mum Allocated)
Maximum Output at
PoE Switch Port (Maxi-
mum Allocated)
0 PoE and PoE+ 0.44W–12.95W 15.4W 16.2W
1 PoE and PoE+ 0.44W–3.84W 4.0W 4.2W
2 PoE and PoE+ 3.84W–6.49W 7.0W 7.4W
3 PoE and PoE+ 6.49W–12.95W 15.4W 16.2W
4 PoE+ only 12.95W–25.5W 30.0W 31.6W
Power allocation and power budget concepts
The switch is a smart switch in that it can allocate the required power to a connected device
by using a prioritization scheme: By default, power is supplied in ascending port order (that is,
lower port numbers are served first) until the power budget is consumed and insufficient
power remains to allocate to the next device. When less than 7W of PoE power is available
on a port, the port PoE LED lights yellow, and the attached device does not receive power
from the port. However, the switch continues to send data through the port connection.
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