Power Over Ethernet (PoE)



With the introduction of a new range of Wifi products and Switches from the manufacturer WiTek we though now would be a good time to provide some information on some POE information.




POE - Power Over Ethernet

Power Over Ethernet , as the name suggests, is the means of allowing the delivery of electrical power along with data through ethernet cabling.
This means that it is possible to allow connectivity of a network related product while also powering the device from a POE power supply. The usual terms for the power supply in this case would be a PSE (Power Sourcing Equipment) and PD (Powered Device). Ethernet cable (CAT5e/CAT6/CAT6a) is made up of 4 pairs of twisted cables. First PoE standards used two pairs to transmit data and two pairs to conduct the power, newer POE standards use all 4 pairs for power and data together.
POE brings the benefits of using a single CAT cable, simplifying and reducing costs of cable runs.

This blog is intended to give some basic POE information, it is by no means an extensive guide but will relate to many of the products that we sell here at Mast Digital.


Examples of PSEs (Power Sourcing Equipment):
POE Injectors
POE Switch
HDMI over Cat6 Transmitter


Examples of PD (Powered Devices):
IP Camera
Wireless IP Bridge
HDMI over Cat6 Receiver



Things to consider: POE Budgets. POE Switches and Power Supplying Equipment will have POE output budgets which you always have to keep in mind. Single outputs will have limits (either stated in Watts or stated as IEEE802.3 standards) and an overall POE budget for the switch. If the overall budget of a POE switch is 60W and there are 4 ports each with 30W max output, you will only be able to use two of the ports at 30W before you go beyond the switches POE budget.

Active / Passive?
In a passive POE system the injector does not communicate with the powered device to determine if it needs power or what power type it needs and simply passes the power onto the device (whether it needs it or not) for this reason it is important to check that the end device is connected to the correct PSE or else it could be damaged. An example of a Passive POE system is the Ubiquiti NanoStation AC Loco which uses 24V DC Passive power.

An Active POE System is when the PSE communicates with the PD to find out firstly, "Does the PD require power?" and secondly "What type of Power is required?". An example of an Active POE system is a Hikvision NVR connected to a Hikvision IP camera using "plug 'n play". Active POE is generally thought to be safer for any devices that do not require POE as they shouldn't receive any power that could damage them. The only downside to Active POE such as IEEE802.3af devices is that both the PSE and the PD need to be compatible.

Devices are now available to convert 802.3af/at devices to 24V Passive and can be useful when attaching some new network devices to an already existing POE switch.

 



IEEE 802.3af/at/bt standards

The original IEEE802.3af standard provides up to 15.4W of DC power but as the technology has improved and the powered devices have increased their power requirements we now have additional types of POE that we typically use within the CCTV industry. Typically PTZ cameras have a higher power consumption than a standard fixed camera, and as such they were traditionally powered with separate 24VAC Power Supplies, requiring additional cabling to be run. A more modern solution is to use a higher power option of POE such as IEEE802.3at or IEEE802.3bt . See the chart below which outlines the differences and power limitations of each of our commnonly seen IEEE802.3 POE standards.  One of the smaller PTZs such as the DS-2DE4225IW-DE will require more power (20W) than an IEEE802.3af injector can offer, in this case you could use an 802.3at (30W injector).

POE Switches
POE Switches are network switches that can also supply power to POE powered devices.

The POE switches that we sell are compatible with IEEE802.3af, but they also have the benefit of working with 802.3at devices and in the case of some can even provide enough power for 802.3bt devices (see our Noctis Pro POE switches with up to 65W for port1). This feature makes these switches ideal for CCTV applications, with the ability to power Fixed cameras, PTZ cameras and also Wireless IP links.

There is a huge range of POE Switches nowadays with various features and functions, some for 24V passive others with 802.3af/at/bt. Some switches will automatically detect which type of POE power it needs to output to enable to PD, whereas other switches need some kind of user interaction to turn the power on. Another thing to look at when speccing your POE switches is the network capabilities with varying speeds and connection options, some POE switches allow GB speeds whilst others are limited to 10/100 connections. Upload ports generally give a network connection, but without any POE power which makes them ideal for connecting to a network/router/NVR LAN port and some switches also offer SFP (Fibre) connections for the uplink.



POE Injectors
A POE injector is like a single port POE switch, generally allowing a connection to a network and then introducing power before continuing on with the power&data combined.

POE repeater
These relatively simple devices allow you to extend cable runs beyond the standard '95m rule', they can sometimes be daisy chained.



POE Splitters
These devices allow you to take a single cable which is carrying POE and then split it out to 2 (or more) POE powered devices.

PoE Special Items.

There are a handful of PoE devices which are rarely mentioned, but are there to aid in a very specific scenario:

POE combiners/splitter kits which allow for two POE devices to be connected to two ports of a POE switch over a single CAT cable.

POE over Coax extender : Allows for POE to be run over a coax cable, allowing for long distance cable runs and also to use network devices over a pre-existing coaxial cable run.