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IEEE 802.3af

The IEEE working group802.3af deals with the standardization of the power supply of Data Terminal Equipment( DTE) via Medium Dependent Interface( MDI). This is the PoE architecture, Power over Ethernet (PoE).

The Power over Ethernet (PoE) working group is working on solutions for powering Ethernet devices. These include VoIP telephones, web cameras and access points( AP) of WLANs. Other areas of application include building automation, point-of-sale terminals or access systems. The standardization of the supply voltage includes compatibility and security to previous Ethernet devices. For the power supply, there is only one MDI connector over which the data and the power supply are routed. The compatibility of the power supply over twisted copper cables for 10Base-T, 100Base- TX and 1000Base-T devices is guaranteed, as well as that no damage is done to existing RJ45 Ethernet devices.

PoE standards

PoE standards

With 802.3af, power is transmitted over two pairs of wires. IEEE 802.3af has standardized power classes 1 and 2 as output powers for the power sourcing equipment( PSE), with powers of 4.0 W and 7.0 W, respectively. The supply voltages are 44 V, and the sourcing current is 350 mA. Higher power values are achieved with the IEEE standards 802.3at and 802.3bt. However, the bt standard, known as PoE++ works with four wire pairs, 4PPoE.

802.3af knows two modes: In mode "A", power is supplied via the wire pairs used by Ethernet, and in mode "B", power is supplied via unused wire pairs. The first mode is called phantom power, the second spare pair power.


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