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Wiring
Implementation
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
can cease power transmission if the switch power budget is at maximum
usage and new powered devices, connected to ports with higher priorities
become active.
The IEEE 802.3af standard defines two methods for delivering DC power
over twisted pair cable by a switch to powered devices. These methods
are known as Modes A and B, and identify the individual wires that carry
the DC power within the cable from the switch to powered devices.
Twisted pair cabling typically consists of eight wires. With 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. At higher speeds, 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 GS980MX/28PSm and GS980MX/52PSm switches support powered
device Classes 0 to 4 up to 30W, using Mode A.
The wiring modes for the GS980MX/10HSm and GS980MX/18HSm
switches are as follows:
Classes 0-4 (Type 1 or 2 up to 30W): Mode A (MDI-x)
Classes 5-6 (Type 3 up to 45W/60W): Mode A (MDI-x) plus Mode
B (MDI-x, MDI)
Classes 7-8 (Type 4 up to 75W/90W): Mode A (MDI-x) plus Mode
B (MDI-x, MDI)
Powered devices in classes 0 to 4 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.
GS980MX Series Installation Guide for Virtual Chassis Stacking
47
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