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How Much Do You Know About PoE?

Power over Ethernet (POE) is a technology that lets network cables carry electrical power. This article will introduce some information about PoE like its advantages, applications, work principle and connection.  

Power over Ethernet (PoE) has been widely used in these areas like VoIP telephony, wireless LANs, IP video security and access control. It can minimize the number of wires that must be strung in order to install the network. Compared with traditional wiring, it has the features of saving cost, easier maintenance, and greater installation flexibility. But what’s PoE?

Basic Concepts

Power over Ethernet (POE) is a technology that lets network cables carry electrical power. It’s defined cross a single network link which includes three basic components. First, it’s PSE, which stands for power sourcing equipment, an equipment delivering power to the cable. Second, it’s PD (power device) receiving power from the cable. The third is the cable itself.

Typical PDs IP cameras and wireless access points. The PSE is normally a PoE switch or a midspan power injector, patched in to add PoE capability to a non-PoE network switch channel or similar.

  • Time and cost saving- PoE is good to reduce the time and cost of having electrical power cabling installed. Then the network cables do not require a qualified electrician to fit them, and can be located anywhere.
  • Great flexibility- Without being tethered to an electrical outlet, the PDs (IP cameras, wireless access points) could be located wherever they are needed most.
  • Safety- Safety is also an important advantage. PoE delivery is intelligent and it is designed to protect network equipment from overload, or incorrect installation.
  • Reliability and scalability- PoE power comes from a central and universally compatible source, rather than a collection of distributed wall adapters. It can be backed-up by an uninterruptible power supply, or controlled to easily disable or reset devices. It has power available on the network, which makes installation and distribution of network connections simple and effective.

At first, PoE was applied in VoIP phones which have a single connection to a wall socket, and can be remotely powered down, just like with the older analog systems. PoE could also be used in IP cameras. It is ubiquitous on networked surveillance cameras where it enables fast deployment and easy repositioning. Wifi and and bluetooth APs and RFID (radio frequency identification devices) readers are commonly PoE-compatible, to allow remote location away from AC outlets, and relocation following site surveys.

Work Principle

PoE operates over standard network cable like Cat 3, Cat 5, Cat 5e or Cat 6 using conventional RJ45 connectors. The principles of carrying electrical power over Cat5 are similar to those of other power distribution systems, but as the power is being transferred over light-duty cable for long distances, there will be significant power loss and voltage drop.

In order to work with the existing standard for Ethernet data, the arrangement and connection to the cabling used for PoE is slightly different from conventional power wiring. Cat5 cable has a bundle of 8 wires, two four twisted pairs. In the most common type of Ethernet, 100BASE-T or Fast Ethernet, only two of the four pairs are used to carry data, each pair carrying a signal in one direction. These are known as the data pairs, and the remaining two are unused and are referred to as the spare pairs.

Although each data signal can be carried within a single pair, PoE treats each pair as a single conductor (a reason for this is that using both wires halves the overall resistance). As electrical current must flow in a loop, two pairs are required to allow power to be carried by the cable, and either the data or spare pairs can be used for this. The PD must be able to accept power from whichever pairs the PSE delivers it to.

PoE Connection

There are two ways of PoE connection. A PoE switch is a network switch that has power over Ethernet injection built-in. Just connect other network devices to the switch. Then PoE can detect whether they are PoE compatible and enable power automatically. PoE switch is available to suit all applications, from low-cost unmanaged switches with a few ports to complex multi-port rack-mounted units with sophisticated management.

A midspan or PoE injector is utilized to add PoE capability to regular non-PoE network links. Midspans could be used to upgrade existing LAN installations to PoE, and provide a versatile solution where fewer PoE ports are required. Upgrading each network connection to PoE is as simple as patching it through the midspan, and as with PoE switches, power injection is controlled and automatic. Midspans are available as multi-port rack-mounted units or low-cost single-port injectors.

Since new Ethernet-enabled devices expanded geometrically, the need to power these devices from standard AC power outlets has become a limiting factor. PoE is created to supply power to network devices over the same standard Cat5 cabling that carries the data. Devices can be installed wherever structured Ethernet wiring is locatedFeature Articles, without the need for AC power outlets nearby. Those special benefits can explain why PoE is so popular.

Article Tags: Power Over Ethernet, Power Over, Over Ethernet, Electrical Power

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I'm currently working as a Telecom Engineer in Fiberstore, an innovative company providing fiber connectivity network solutions for carriers, ISPs, content providers and networks.

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