Wiring Implementation - Allied Telesis AT-GS924MX Installation Manual

Chapter 1: Overview
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 PSE, such as a switch, to PDs. These
Implementation
methods, known as Alternatives A and B, identify which of the wires within
the cables are to carry the DC power from the switches to the PDs.
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 PD. With Alternative 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
Alternative B, the power is provided over 4, 5, 7, and 8, which are spare
wires.
The ports on the AT-GS924MPX and AT-GS948MPX Switches deliver the
power using pins 4, 5, 7, and 8, which corresponds to Alternative B in the
IEEE 802.3af standard. Therefore, the switches can support PDs that use
Alternative B to receive power.
PDs that comply with the IEEE 802.3af and 802.3at standards are
required to support both Alternative A and B. However, non-standard PDs
and PDs that were manufactured before the completion of the IEEE
802.3af and 802.3at standards and that support only Alternative A will not
work with the switches.
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