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Power over Ethernet: What is it and why is it useful?

NetworkTigers discusses Power over Ethernet and why it is useful.

PoE or Power over Ethernet is a simple solution for a common problem with security device setup. Network devices such as IP cameras and wireless access points are often physically separated by space and obstacles (e.g., walls) in a building. However, they still need to be powered by electricity to work. This limitation means placement is severely restricted by building design, existing AC electrical outlets, and conduit extension capabilities.

Power over Ethernet (PoE) also known as IEEE 802.3af, allows electrical power and data to be transmitted simultaneously over a standard Ethernet network cable. This means that devices such as wireless access points, IP cameras, and VoIP phones can receive data and power from a single Ethernet cable, eliminating the need for separate power cables and power adapters. PoE can be delivered using either a PoE-enabled network switch or a PoE injector, which adds power to the Ethernet cable. PoE has become increasingly popular in modern network installations because it simplifies cabling, reduces installation costs, and improves reliability.

What is the original IEEE 802.3af-2003 PoE standard?

In a standard Ethernet cable, only two pairs of wires transmit data, while the other two pairs are unused. The PoE-enabled switch or injector sends DC power over these unused wire pairs while the data signals are transmitted over the other pairs. IEEE 802.3af-2003 PoE injects DC voltage onto the unused wire pairs in an Ethernet cable.

The PoE-enabled switch or injector includes a detection mechanism that first checks if the connected device is PoE-compatible. If the device is compatible, the switch or injector then negotiates the amount of power to be delivered based on the device’s power requirements.

At the receiving end, the PoE-compatible device, such as a wireless access point or IP camera, includes a Power Device (PD) that separates the power and data signals and converts the DC voltage to a usable voltage level for the device. The device can then use the supplied power to operate, eliminating the need for a separate power source.

Overall, IEEE 802.3af-2003 PoE allows power and data to be transmitted over a single Ethernet cable, simplifying cabling and installation and making it easier to deploy devices where power outlets may not be available.

PoE works via connections through four twisted pairs of copper Ethernet cables. In the original PoE standard, power is sent over two cable pairings, and data is sent over the other two. Transmissions are separate in the first IEEE 802.3af-2003 PoE. Original Poe provides up to 15.4 W of DC power on each port. 

What is PoE+?

PoE+, also called PoE Plus or the updated IEEE 802.3at-2009 PoE standard, uses the same system but transmits more power. The upgrade allows for 30 W of power to devices such as VoIP phones, alarm systems, security cameras, and wireless access points. 

For many older devices, 30 W of power is plenty. However, when your business requires a PoE setup for network devices that involve LED lighting, flat screens, or even some retail POS terminals, the PoE+ power supply still falls short.

Understanding the new 802.3bt PoE standard

Think of the new 802.3bt PoE a little like the emerging WiFi 6. It is vastly more efficient and faster, but the setup is also more expansive. The highway of data transmissions becomes wider, allowing more information to be sent along more channels. However, the 802.3bt PoE standard was developed and released by the IEEE at the end of 2018, meaning this technology already has a proven track record of success.

Unlike the original PoE and PoE+, power is run over all four twisted wire pairs instead of just two. This allows for greater flexibility in use and a better power supply. It also can minimize power loss by using the existing cable more efficiently to run power along both lines. 802.3bt PoE vastly boosts capacity. It provides anywhere from 60 to 100 W. 

802.3bt PoE, sometimes called PoE++, encompasses two branches of this more efficient setup. PoE++ Type 3 can run 51 W to powered devices, with a maximum power of 60 W per port. It can support more developed devices, such as video conferencing gear and multi-radio wireless access points. Meanwhile, Type 4, sometimes called higher power PoE, runs even hotter. Type 4 PoE++ delivers 71.3 W to powered devices. It has a maximum port power of 100 W per port, meaning that it can power even laptops and flat screens. 

How does PoE++ work?

The development of using both sets of twisted cables for power took time. However, when power and data transmissions are run along the same wiring, the two communications don’t cause interference with each other. This has to do with the different frequencies between electricity and data transmissions. Electricity has a low frequency of 60 Hz or even less. Data, meanwhile, has a high-frequency transmission. Data transmissions can range from 10 million to 100 million Hz. This allows electricity and data to run along the same cable without interference, as they run at opposite ends of the frequency spectrum and do not clog up each other’s transit. 

You might consider PoE, whether PoE+ or the more powerful PoE++ Type 3 or Type 4, for many of your building management needs. Consider PoE splitters, repeaters, extenders, and ethernet switches to maximize what they can do for you. All of these extend PoE access to even more devices or boost data and power to allow you to get the biggest bang for your buck out of your network setup. 

Gabrielle West
Gabrielle West
Gabrielle West is an experienced tech and travel writer currently based in New York City. Her work has appeared on Ladders, Ultrahuman, and more.

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Power over Ethernet: What is it and why is it useful?