Chapter 1: Overview
The IEEE 802.3af standard defines two methods by which a PSE, such as the switch, can transmit DC power over twisted-pair cables to PDs. These methods, known as modes A and B, identify the wire strands the switch should use when sending DC power to a PD.
Twisted-pair cabling typically consists of eight strands. With 10Base-T and 100Base-TX devices, the strands connected to pins 1, 2, 3, and 6 on the RJ-45 connectors carry the network traffic, while strands connected to pins 4, 5, 7, and 8 are unused. With 1000Base-T devices, all eight strands are used to carry network data.
It takes four strands 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 strands.
The ports on the AT-9000/12POE and AT-9000/28POE switches deliver the power using pins 4, 5, 7, and 8, which corresponds to Mode B 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 4, 5, 7, and 8.