May | 2015 | video security guide

Power over Ethernet (PoE) is a mechanism for supplying power to network devices over the same cabling used to carry network traffic. In this technology no infrastructure upgrade is necessary.
A digital security camera normally requires two connections to be made when it is installed:

A network connection, in order to be able to communicate with video recording and display equipment and a power connection, to deliver the electrical power the camera needs to operate. However, if the camera is PoE-enabled, only the network connection needs to be made, as it will receive its electrical power from this cable as well and this enables the elimination of a separate cable solely for power use.

Cisco was one of those manufacturers that began including PoE capability within its switches in 2000.

Advantage of the Ethernet cable
• The challenge during installation is to calculate the total power consumption required so it is less than the power budget of the switch. The total power consumption requirement of all equipment that will be connected to a specific switch on a network needs to be calculated to ensure sufficient power is available per switch.

• Without being tethered to an electrical outlet, devices such as IP cameras and wireless access points can be located wherever they are needed most and repositioned easily if required.

• POE power comes from a central and universally compatible source, rather than a collection of distributed wall adapters.

• Having power available on the network means that installation and distribution of network connections is simple and effective.

• Wifi and Bluetooth APs and RFID readers are commonly PoE-compatible, to allow remote location away from AC outlets, and relocation following site surveys.

• Unlike standards such as Universal Serial Bus which also power devices over the data cables, PoE allows long cable lengths.

• Simply connect other network devices to the switch as normal and the switch will detect whether they are PoE-compatible and enable power automatically.

There are several standardized or ad-hoc systems which pass electrical power along with data on Ethernet cabling. Two of them have been standardized by IEEE 802.3: standard IEEE 802.3af and new prepared standard IEEE 802.3at.

In addition to standardizing existing practice for spare-pair and common-mode data pair power transmission, the IEEE PoE standards provide for signaling between the power source equipment (PSE) and powered device (PD). Up to a theoretical 51 watts is available for a device, depending on the version of the standard in use and the vendor of the hardware.

A midspan (or PoE injector) is used to add PoE capability to regular non-PoE network links. 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. It is also possible to upgrade powered devices, such as IP cameras, to PoE by using a PoE splitter.

The following chart shows the power consumption at both the PSE and the PD.