Allied Telesis AT-x930-28GPX, Installation Manual

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x930 Series Installation Guide for Virtual Chassis Stacking
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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
Implementation
The IEEE 802.3af standard defines two methods for the delivery of DC
power over copper cable from a switch to the powered devices. These
methods, known as modes A and B, identify the wires within the cable that
carry the DC power from the switch to a powered device.
Copper 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 PD. With Mode A, the 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, the power
is provided over the spare wires.
The ports on the AT-x930-28GPX and AT-x930-52GPX Switches deliver
the power using pins 1, 2, 3, and 6, which corresponds to mode A in the
IEEE 802.3af standard. Powered devices that comply with the IEEE
802.3af standard are required to support both power delivery methods.
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.