Data Transmission

What Is Power-over-Ethernet?


PoE is short for Power Over Ethernet, is a methods of carrying both data and power to a device over copper cable. This is accomplished by running a twisted-pair copper cable, such as a Category 5 cable, from a device to a mid-span or endpoint, where the cable can be connectorized using standard RJ-45 or similar modular connectors. While power and data are carried over the same physical channels, there is no interference between them because the power is direct current (DC) and the data is run on top of the DC voltage at frequencies ranging from 10 MHz (Category 3) to 500 MHz (Category 6A).

PoE was first introduced by Cisco in 2000 to support their newly deployed Voice-over-Internet-Protocol (VoIP) services. PoE was an obvious backbone for VoIP technology because it was not only able to meet the high-bandwidth requirements of VoIP, but was also able to provide low-voltage power (10 W) to their VoIP devices. In 2003, the IEEE published the first PoE standard, 802.3af, which allowed 12.95 W of power to be available to the device.

Initially, PoE was essentially limited to this particular application, as most other devices that required both power and data communications in order to operate, such as digital security cameras, required more power than a two-pair copper cable could provide at the time. Recognizing the need for more power, the IEEE released the 802.3at standard that allows up to four-pair copper cables to meet, and in some cases exceed the minimum power requirements of these types of devices; currently, the IEEE is developing another standard — 802.3bt — that would further increase the amount of power copper cables can carry. Depending on the design and specification, category cables can now provide up to 100 Watts of power to a device, as well as support 10 Gigabit Ethernet.