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Chapter 1: Overview
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.
Wiring
The IEEE 802.3af standard defines two methods for delivering DC power
over twisted pair cable by a switch to powered devices. These methods
Implementation
are known as Modes A and B. They identify the individual wires that carry
the DC power within the network cables from the switch to powered
devices.
Twisted pair cabling typically consists of eight wires. With 10Base-T and
100Base-TX devices, the wires connected to pins 1, 2, 3, and 6 on the RJ-
45 connectors carry the network traffic while the wires connected to pins 4,
5, 7, and 8 are unused. With 1000Base-T devices, all eight wires are used
to carry network data.
It takes four wires to deliver DC power to a powered device. With Mode A,
power is delivered on pins 1, 2, 3, and 6. These are the same pins in
10Base-T and 100Base-TX devices that carry the network data. With
Mode B, power is provided over the spare wires.
The ports on the AT-GS980M/52PS Switch deliver power using Mode A.
Powered devices that comply with the IEEE 802.3af standard are required
to support both Modes A and B. Legacy devices that do not comply with
the standard will work with the switch if they are powered on pins 1, 2, 3,
and 6.
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