What is Power over Ethernet (POE)

The Importance of Mode A or Mode B (POE)

What you need to know

Power over Ethernet is a standard that allows you to power certain network or IP devices over that same data cable that connects it to your network. There are 3 primary implementations of POE that will be described individually. Before we go into that, there is some information that you need to know about your product to determine which implementation and hardware you will need to get your desired results.

  1. Is the IP device/camera you are using true POE or not?
  2. Does your network switch supply POE power?

The first question is the most important, because it determines all of your remaining hardware requirements. Below are examples for each implementation type and why.

In the first example you have a switch that supplies POE and are looking to get an IP camera that supports true POE, in this situation you only require a network cable running directly between the switch and the camera. This is because the camera is capable of being powered over the Ethernet itself and the switch supplies POE. (See image below)


(POE switch directly connected to a true POE camera)

In the second example you are interested in an IP camera model that supports true POE, but you do not have a switch or router that provides POE. In this event you will need a POE injector in addition to the switch/router and your POE IP camera. You will connect them like the image below.


(Standard switch connected to a true POE camera via a POE Injector)

In the final example you have a switch/router, that does not provide POE and you are interested in an IP camera that does not support true POE. In this case you can use a POE injector/Splitter kit. To connect this configuration you would connect your switch/router to the POE injector, Connect the POE injector to the POE splitter, and the POE splitter will connect to the camera as you see below.


(Standard switch connected to a standard IP camera via a POE Injector Splitter)

Below you will see a close up of the POE splitter and its connection to the camera. The splitter has both power and Ethernet outputs to connect the network and power separately.

Power over Ethernet Glossary

PoE – Power Over Ethernet: A relatively new technology that allows PoE-enabled Ethernet networked devices to receive power (as well as data) over existing CAT-5 Ethernet cable without the need to make modifications to it.

PD - Powered Device: A Ethernet device that receives power over Ethernet. It could be a PoE-enabled IP phone, a wireless access point, a serial device server or any other IP device that requires power.

PSE – Power Sourcing Equipment: The network PoE element that inserts power onto an Ethernet cable. It may be an endspandevice, such as a PoE-enabled switch, or a midspan device located between the switch and the PD.

Midspan – A midspan device is a PSE that inserts power onto the Ethernet cable. It is situated between the LAN switch and the PD. Typically, midspan devices are added to existing networks to allow the use of PoE-enabled PDs.

Endspan – An endspan device is typically a switch that incorporates PoE capabilities. Endspan devices often are implemented when a new network is created, to avoid adding midspan devices as well as the switch.

IEEE 802.3af – An IEEE standard (ratified in June 2003) that defines the transmission of power over Ethernet infrastructure. Also called Data Terminal Equipment (DTE) Power via Media Dependent Interface.

Ethernet - Ethernet, an IEEE 802.3 standard, is the most commonly installed computer local area network technology. Ethernet uses a bus or star topology and relies on the form of access known as Carrier Sense Multiple Access with Collision Detection (CSMA/DC) to regulate communication line traffic.

CAT-5 – Category 5 cable is the standard type of UTP cable used for horizontal Ethernet wiring. CAT-5 cable contains eight conductors, of which four are used for data communication in 10BaseT and 100BaseTX Ethernet.

Access Point – A wireless LAN device that interfaces with a wired Ethernet LAN.

RJ-45 – Registered Jack Standard 45. The RJ-45 is a single-line jack for digital transmission over ordinary phone wire, either untwisted or twisted. It is the interface of Ethernet standards 10BaseT and 100BaseT. The connector has eight connector points and can accommodate up to eight wires.

UTP – Unshielded Twisted Pair. The cable used for most telephone wire, and is also used for some computer-to-computer communications. It contains pairs of unshielded wires twisted together and is an inexpensive and relatively low-noise way to transmit signals. CAT-5 cable is UTP.

STP – Shielded Twisted Pair: A cable type sometimes used in networking. Each pair has a metal sheath around it for protection against interference.

SELV – Safety Extra Low Voltage: A circuit which is so designed and protected that, under normal and single fault conditions, its voltages do not exceed a safe value (60 VDC).

MDI / MDI-X – Media Dependent Interface: In Ethernet cable wiring, the concept of transmit and receive are from the perspective of the end device (PC network card, IP phone, device server, wireless access point, etc). The end device is wired as an MDI—data is transmitted on pins 1 and 2, received on pin 3 and 6. The hub, switch or router used on the network is wired as an MDI-X in which the perspective is reversed, and pins 1 and 2 are the receive pins, pins 3 and 6 are the transmit pins. To connect two end devices (e.g. two computers with network interfaces) a crossover cable is required.

DTE – Data Terminal Equipment: A communications element that is a source of data, as opposed to Data Communications Equipment (DCE), which accepts data from the DTE and transfers it to another DCE. PCs are a typically DTE.

Galvanic Isolation – Electrically isolating two parts of a circuit so that no current can flow between them. This is accomplished using a transformer or optocoupler and is often done to maintain safety for the equipment and personnel using it.

DC/DC converter – An electronic device that converts DC power at one voltage to DC power at another voltage (may be higher or lower voltage). The input and output sides of the converter typically are galvanically isolated from each other.

Switch – A networking device that connects multiple computers on a LAN so they can communicate with one another, the rest of the network and the internet. Unlike a hub, users connected to a switch do not share the available bandwidth. Each switch port runs at the full bandwidth of the switch port. A switch keeps track of MAC addresses attached to each of its ports and switches data to the intended recipient.

Hub – A connection device for networks that allows multiple segments or computers to connect and share packets of information. Hubs merely reproduce and re-send data pulses and do not switch the data based on its address or content.

LAN – Local Area Network. A communications network connecting a group of computer, printers, and other devices located within a relatively limited area (such as a home, office or small building). A LAN allows any connected device to interact with any other on the network. A LAN in turn often connects to other LANs, and to the Internet or other WAN.

Phantom Feeding – A technique for supplying power to a circuit in which the DC voltage is applied equally to two signal conductors, usually by simplexing the DC power using the center tap of signal coupling transformers. The DC power is removed from the signal at the receiving using another set of coupling transformers.

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