Allied Telesis AT-8100L/8POE User Manual

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Stand-alone Switch Installation Guide for 8100L and 8100S Series Switches
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The switch can handle different power requirements on different ports. 
This enables you to connect different classes of PoE equipment to the 
ports on the switch.
Port
Prioritization
If the power requirements of the powered devices exceed the switch’s 
power budget, the switch denies power to some ports based on a system 
called port prioritization. You may 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:
Critical
High
Low
Ports set to the Critical level, the highest priority level, are guaranteed 
power before any of the 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. Ports that are connected to 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 of 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 is at maximum 
usage and new powered devices, connected to ports with higher priorities, 
become active.
You can use port prioritization on dual power supply PoE switches to 
protect your important networking devices from loss of power should one 
of the power supplies fail or lose power. By limiting the power 
requirements of the critical devices connected to a switch to less than 185 
watts, the PoE power provided by a single power supply, a switch will have 
sufficient power to support the critical devices even if it has only one 
functional power supply.