Allied Telesis AT-S81 - Manual (Page 105)

AT-S81 Management Software User’s Guide
Section I: Using the Menus Interface 105
There are three priority levels:
ˆ Critical
ˆ High
ˆ Low
Ports designated as critical receive power before any other ports with a
lower priority. Always assign the critical priority level to your most
important network devices. If there is not enough power to support all the
ports set to the critical priority level, then power is provided to the ports
based on port number, in ascending order.
Ports set to the high level receive power only after all the critical ports
receive their power. If there is not enough power to support all the ports
set to the high priority level, then power is provided to the ports based on
port number, in ascending order.
The lowest priority setting is low, the default setting for all ports. Ports with
low priority receive power only after the critical and high level ports receive
their power. If there is not enough power to support all the ports set to the
high priority level, then power is provided to the ports based on port
number, in ascending order.
PoE Device
Classes
The IEEE 802.3af standard specifies four classes for powered devices
based on their power usage. The classes are defined in Table 2.
Note
The standard specifies five classes, but the fifth is reserved for
future use.
Manufacturers set the power class of their PoE powered devices. You
cannot adjust this. You can view the power class of each device in the
Power Over Ethernet menu, shown in Figure 26 on page 107.
Even though each port is capable of supplying up to 15.4 W, the standard
calls for a maximum power consumption of 12.95 W, 2.45 W less than the
port can supply. This extra capability is to compensate for possible line
Table 2. Power Classes for Powered Devices
Class Power Usage
0 (Default) 0.44 W to 12.95 W
1 0.44 W to 3.84 W
2 3.84 W to 6.49 W
3 6.49 W to 12.95 W