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What is Power Over Ethernet (POE)?

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  • Difficulty Level : Medium
  • Last Updated : 10 Feb, 2022

Power Over Ethernet (POE) is a technique used for building wired Ethernet local area networks (LANs) which use Ethernet data cables instead of normal electrical power cords and wiring to carry the electrical current required to operate each device. The transfer of power through network cabling is possible because of the coupling of data transmission and power-providing hardware on the same RJ45 Ethernet connection.

In 2003, the PoE standard was created to accommodate devices such as wireless access points (APs). Before then, several types of proprietary PoE were employed by different companies to give PoE capabilities. Today, some of these proprietary PoE devices are still in use. Installers of PoE devices must discover where these older, proprietary devices are placed since they may be incompatible with subsequent standard PoE devices. AP installations are easier and more adaptable with today’s standard PoE devices, especially in ceilings, which might be difficult to wire for electrical power.

Consider a scenario where we want to install a digital security camera,

Power over Ethernet

Power over Ethernet

Here two connections are usually required :

  1. To communicate with video recording and display devices, you’ll need a ‘Network Connection’.
  2. A ‘Power Supply’ is required to provide the electrical power to the camera it requires to operate.

But if the camera is POE-enabled, only the network connection is required to be formed because it will get its electrical power as well from this cable.

Working of POE:

The working of POE is solely dependent on the flow of the electrical current which must enter an Ethernet data connection at the power source end and exit at the device end. With Ethernet, the data signal and the power current may be maintained separately so that neither interferes with the other. An injector allows current to flow into the Ethernet wire. If the device on the other end of the wire is PoE-compatible, it will work without any changes. If it isn’t PoE-compatible, you’ll need to install a picker, or tap, to remove the current from the cable. The current that has been picked up is directed to the power jack.

Why use POE?

There are several advantages to specifying Power over Ethernet in an installation :

  1. By lowering the time and cost of installing electrical power cabling Network cables do not require the installation of a certified electrician and may be placed almost anyplace.
  2. Devices like IP cameras and wireless access points may be placed wherever they are needed most and relocated quickly if necessary because they are not linked to an electrical outlet.
  3. The intelligent POE distribution system protects network equipment from overload, underpowering, and wrong installation.
  4. Installation and deployment of network connections are straightforward and effective when there is electricity accessible on the network.
  5. Rather than a variety of scattered wall adapters, POE power comes from a single, globally compatible source. It can be powered by an uninterruptible power source, or it can be remotely operated to deactivate or reset devices.

History of POE:

Devices like cameras used to require a signal connection to relay the picture back to a recorder before Ethernet communications. Local power supplies were also required to power these gadgets. Companies began running a combination of signal and power cables with a power supply sending electricity from the head end recorder site because cameras and similar devices are frequently deployed in regions where local power may not be accessible.

Cameras began using multi-pair UTP cables, such as CAT5, to convey a combination of signaling and power as signaling and power technology advanced. On one or two of the four pairs of a CAT5 cable, signaling was conveyed, while power was transmitted on the remaining two pairs. This simplified installations by using fewer cords to do the same purpose.

This functionality was lost when endpoint signaling switched from analog to IP broadcasts. The Institute of Electrical and Electronics Engineers(IEEE) designed and standardized Power over Ethernet in 2003.

Devices that use POE:

POE is compatible with the following devices that need equal or less than 30 watts (W) of power :

  1. VoIP phones
  2. IP cameras
  3. Network audio
  4. Tilt and zoom robotic cameras
  5. Large TVs and liquid crystal display screens
  6. wireless AP devices
  7. IP, VoIP, and video telephones

POE+ or High-power PoE:

The 802.3AT standard, often known as PoE+ or high-power PoE, stipulates that Power Sourcing Equipment may deliver 30W of power to assure 25.5W at the endpoint. Both the switch and the endpoint device must be IEEE compliant to ensure a successful negotiation. Some device makers, on the other hand, have developed their own PoE implementations.

Transmission of electricity through Ethernet cabling may be accomplished in three ways. Mode A (also known as common-mode data pair power), Mode B (spare-pair power), and 4PPoE (4-Pair power) are the three modes available. Power is sent over the same cable pair as the data pairs in a 10Base-T or 100Base-TX transmission in Mode A. The spare pairs are used in Mode B, while all four pairs of the Ethernet cable are used for power transmission in 4PPoE. 

The specifications of each mode are shown below.

    PoE Mode        Ethernet Cable pairs utilized    

    Pin allocation  

Mode A 

Data Pairs

Pins : 1, 2 & 3, 6

    Pins 1, 2 = Positive Voltage (DC+)    

    Pins 3, 6 = Negative Voltage (DC-)     

  Mode A

Spare Pairs

 Pins : 4, 5 & 7, 8

Pins 4, 5 = DC+

Pins 7, 8 = DC-

  Mode A

All 4 Pairs

Pins 1, 2 and 4, 5 : DC+

Pins 3, 6 and 7, 8 : DC-

The following devices are supported by this standard :

  1. Video Conferencing
  2. Wireless, high-performance APs
  3. Video surveillance cameras
  4. Security card readers
  5. LED lighting

Upgrading to POE:

It’s simple to integrate POE into your network, and you can choose either from two routes below :

A Power over Ethernet switch (POE switch) is a network switch with built-in Power over Ethernet injection. Simply attach other network devices to the switch as usual, and the switch will automatically determine whether they are POE-compatible and turn on the power. From low-cost unmanaged edge switches with a few ports to complicated multi-port rack-mounted systems with sophisticated administration, POE switches are available to meet all applications.

Upgrading to POE

Upgrading to POE

To add POE functionality to non-POE network lines, midspan (POE injector) is required. Midspans may be used to convert existing LAN setups to POE and provide a flexible option when only a few POE ports are required. Each network connection may be upgraded to POE by patching it through the midspan, and power injection is regulated and automated, much as with POE switches. Midspans come in a variety of configurations, including multi-port rack-mounted devices and low-cost single-port injectors.

Upgrading to POE

Upgrading to POE

Endspans and Midspans:

Power Sourcing Equipment (PSE) is a POE equipment that acts as a power source like a POE ethernet switch. PSEs can be used as endspans (e.g., a PoE-enabled Ethernet switch) or as midspans (PoE-enabled Ethernet switch) (a power hub used in conjunction with a non-powered Ethernet switch already in place on the network). Endspans and midspans can both provide electricity to power devices (PDs).

Endspans deliver electricity to the devices directly. Endspans can use either the spare pairs or the data pairs in the cable, which can also be used for Gigabit Ethernet transmissions, according to the requirements. Endspans necessitate PoE-enabled switches, which are often selected for new installations that require new equipment.

Midspans employ an injector which is a powered patch panel that lies between an existing Ethernet switch and the PDs. The PSE is often positioned near to the switch and allows the cable to be routed unimpeded to remote devices. Midspans are only allowed to use the cable’s spare pair, therefore they can’t transfer power across data lines like Gigabit Ethernet connections.

Advantages of POE:

  1. POE is easy to install
  2. Both power and data signals can be carried through Ethernet so it’s a cost-effective solution.
  3. If there is a service outage, PoE immediately pauses power current flows ultimately ensuring safety.
  4. Using Cat5 and Cat6 connections, PoE can currently transport data at 1 gigabit per second (Gbps) — 10/100/1,000 megabits per second. Over a distance of 100 meters, the IEEE 802.3bz PoE standard provides speeds of 2.5 to 5 gigabits per second (m).
  5. POE devices connected to high-security networks are protected in the same way as other network assets.

Disadvantages of POE:

  1. Multiple devices are frequently connected to a single PoE connection. If one device in the stream fails, the entire network goes down.
  2. The maximum power consumption for devices that accept the 2003 PoE standard is 30 W. PoE release IEEE 802.3bz is required for devices that require more power.
  3. Unless PoE extenders or other means are utilized to deliver power, PoE power transmission is restricted to 100 meters.
  4. PoE switches are more costly than regular switches, although combining power and data signals saves money.
  5. Threat actors that wish to breach PoE devices connected to these networks will have an easier time getting access if network security is insufficient.

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