Allied Telesis AT-S62 - Manual (Page 346)

Chapter 19: Power Over Ethernet
346 Section II: Advanced Operations
Port
Prioritization
This section explains port prioritization, a mechanism by which the switch
determines which ports are to receive PoE in the event the needs of the
powered devices exceed the available power resources of the switch. This
discussion does not apply to the AT-8524POE switch since its power
supply can deliver the maximum of 15.4 W to all 24 based ports
simultaneously. This discussion becomes relevant only if, at some later
date, Allied Telesyn releases an AT-8500 Series switch with PoE
capability with a power supply that cannot service all ports simultaneously.
If the powered devices connected to a switch require more power than the
switch is capable of delivering, the switch will deny power to some ports
based on a system called port prioritization. You can use this mechanism
to ensure that powered devices critical to the operations of your network
are given preferential treatment by the switch in the distribution of power
should the demands of the devices exceed the available capacity.
There are three priority levels:
ˆ Critical
ˆ High
ˆ Low
The Critical level is the highest priority level. Ports set to this level are
guaranteed power before any ports assigned to the other two priority
levels. Ports assigned to the other priority levels receive power only if all
the Critical ports are receiving power. Your most critical powered devices
should be assigned to this level. If there is not enough power to support all
the ports set to the Critical priority level, power is provided to the ports
based on port number, in ascending order.
The High level is the second highest level. Ports set to this level receive
power only if all the ports set to the Critical level are already receiving
power. If there is not enough power to support all of the ports set to the
High priority level, power is provided to the ports based on port number, in
ascending order.
The lowest priority level is Low. This is the default setting. Ports set to this
level only receive power if all the ports assigned to the other two levels are
already receiving power. As with the other levels, if there is not enough
power to support all of the ports set to the Low priority level, power is
provided to the ports based on port number, in ascending order.
Power allocation is dynamic. Ports supplying power to powered devices
may cease power transmission if the switch’s power budget has reached
maximum usage and new powered devices, connected to ports with a
higher priority, become active.