802.3af - Power over Ethernet

Power over Ethernet (also referenced as “PoE”) is a method of transmitting power signals over CAT5 and above Ethernet cabling. In areas where power outlets are limited or are unavailable, the most simple way to deploy a networking device would be to use PoE. However, before PoE can be implemented, the networking device must support the 802.3af standard or must be compatible with 802.3af adapters. D-Link currently offers both 802.3af products and adapters to help accommodate your needs.

What are the nitty-gritty details in how Power over Ethernet works?

There are four pairs of wires in a CAT5 Ethernet cable. Wires 1, 2, 3, and 6 are used for sending and receiving data in a Fast Ethernet network. 802.3af utilizes wires 4, 5, 7, and 8 to send power. The amount of power transmitted over these pairs of wires is 48V 0.4A or 15.4W. This power can be transmitted up to 328ft, which is the maximum distance for CAT5 cabling. There are two pieces to a Power over Ethernet setup. The Power Source Equipment, or PSE, is what injects the power onto the unused pairs of wires. The Powered Device, or PD, is what takes the data and power signals coming on all 8 wires and splits them up accordingly. The PD must have a power sensing mechanism so that it will reject power signals that fall out of the acceptable range because they are either too weak or too strong.

Additionally, you can use a PoE Injector and Terminal Unit to send power from a non-PoE Switch to a non-PoE device. The PoE Injector basically sends power over a CAT5 Ethernet cable, and the Terminal Unit accepts, sorts, and distributes the power to the non-PoE device.

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