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What is Power over Ethernet (PoE)?

Feb 25, 2024

What is Power over Ethernet (PoE)?

Power over Ethernet (PoE) is a technology that passes electric power (DC) over a twisted-pair Ethernet cable to powered devices, such as wireless access points, IP cameras, and VoIP phones, in addition to the data that cable usually carries. It enables one RJ45 cable to provide both data connection and electric power to powered devices instead of using a separate cable for each.

PoE became a standard in 2003 and its value was quickly realized. Transporting both power and data across a single cable not only reduced cabling needs but improved safety and simplified installation, thus saving time and reducing cost. The value of PoE also amplified the need for more power to support a wider variety of end devices, resulting in several additions and improvements to the 802.3af standard.

PoE brings several advantages and benefits. First, the delivery of data and power over a standard Ethernet cable eliminates the need for AC/DC power supplies and outlets. This lowers the costs of adding or installing compatible PD equipment since you don’t need an electrician to install power where you want to place your new PDs. Additionally, regular Ethernet cables are rather inexpensive and commonplace. Second, with PoE technology in general, there are fewer points of failure. Connect your PoE switch or PoE injector to an uninterruptible power supply (UPS) bank and your PoE powered devices are guaranteed a constant power delivery, which is important for mission critical PoE edge devices. Third, PoE installations, which utilize managed PoE switches, offer the ability to remotely restart connected PoE devices. That can be done either manually, or automatically based on a schedule. Modern PoE switches are equipped with watchdog functionality (i.e. Powered Device Manager [PDM]) that cuts power to offline devices and then resupplies it so they reboot. This function helps to greatly reduce the downtime of your connected devices.

PoE’s Most Common Applications

PoE is a powerful technology that can change the entire landscape for various businesses, so let’s talk about where it can be used and its most common applications:

VoIP – Voice over IP telephony systems have been a popular solution for office spaces and other commercial settings due to the reduced operational costs and increased reliability of calls over long distances. In call centers and other spaces where power consumption sometimes exceeds available resources, the combination of PoE and VoIP can have a significance and make immediate impact. VoIP was one of the original intentions for using PoE and continues to play a significant role to this day.

Access Points – Wi-Fi, Bluetooth APS, and RFID technologies are now utilized by virtually all modern businesses, and PoE-enabled access points create a cost-effective and versatile solution that facilitates the potential for remote access even when AC units aren't available. Likewise, it allows for easy relocation after site surveys and related assignments. In addition to cost and convenience, access points located in outdoor environments supported by PoE technologies encourage better reliability and easier deployment.

IP Cameras - The use of surveillance cameras that record and store data via an internet-based connection delivers a secure and stable solution by eliminating the need for video recording equipment. It also allows to position cameras on external walls where traditional cabling fittings would not offer a suitable configuration. Through a faster deployment and versatile solution, enterprises can benefit from better protection with a 360° coverage of both permanent and temporary assets without impacting the structural elements.

Other devices to use PoE technologies include Point of Sale terminals, smart clocks, LED lighting, external signage, and a range of products that composed the large ecosystem and power of Internet of Things (IoT) features.

A word about safety: IEEE 802.3af/at/bt compliant PoE technology is extremely safe. PoE injectors and switches will not damage any equipment, even if the equipment is not designed for PoE applications. Before the PSE sends any power to a connected PD, the PSE initiates a handshake procedure that establishes how much power the connected device requires. This procedure uses low voltage and is harmless to any connected device, whether PoE-enabled or not. When the handshake is completed, the PoE injector or switch begins sending power, which triggers the PD to start up. If that handshake is not completed for whatever reason, the PSE never sends any power. It is this built-in feature of all IEEE 802.3af/at/bt-compliant devices that makes PoE technology inherently safe.

There are a variety of devices supporting PoE technology, among them PoE switches, which are network switches that already incorporate PoE functionality and will, once connected, detect all other devices to decipher which ones are PoE-compatible. PoE switches are available in a range of setups, including multi-port rack-mounted units, and deliver power to PoE-enabled devices along with a two-way data connection. PoE injectors, otherwise known as midspans, are used to turn existing LAN equipment into PoE systems. This can be thought of as an intermediary between the network switch and the PoE devices, such as IP cameras. While midspans do require power connections themselves, they subsequently power a range of PoE devices through simple patching. PoE splitters are smart devices that are used to 'tap off' the current PoE power before delivering the reduced but sufficient voltage level to the PoE-enabled device. While they are far less common than both PoE switches and PoE injectors, decision-makers should be aware of their capabilities before committing to any PoE infrastructure.

RAD PoE switches
RAD’s PowerFlow is a series of industrial-grade, managed Fast Ethernet and Gigabit Ethernet switches, with or without Power over Ethernet (PoE) support, which provide stable and reliable Ethernet transmission. Housed in ruggedized DIN rail or wall-mountable enclosures, these switches are specifically designed for harsh environments, such as industrial networks, transportation systems, as well as military and utility market applications where environmental conditions exceed commercial product specifications.

Learn more about PowerFlow PoE switch


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