What is Power over Ethernet? (PoE)

PoE (or Power over Ethernet) is the method of transmitting both power and data across the internal cores of an Ethernet cable and is ideal for getting power to hard-to-reach areas. There are many variants available and the type of PoE you use is ultimately decided by your equipment's capabilities.

Power over Ethernet technology has evolved to be a key part of wireless LAN architectures, smart buildings and enterprise networks.

1) Introduction

Power over Ethernet has become one of those checklist items many enterprises rely on to bring electricity over existing data cables to WiFi access points, firewalls, VoIP telephony appliances and other infrastructure throughout their networks.

PoE’s use has grown substantially since the IEEE standardized it in 2003, and its use will only increase in the coming years as new applications develop. In fact, the Dell’Oro group says that PoE port shipments will total over 624 million over the next five years.

There are a number of drivers for current PoE technology. For example, if you look at WLAN access points, you have increased number of wireless-spectrum bands and higher speeds which require higher power. The new generation of VoIP handsets are now introducing tele-presence features. If you look at surveillance cameras, you have zooming features, you have added analytics. All these new features require higher power requirements.

2) Benefits

The driving ideas behind PoE were to eliminate the need for electrical outlet installation, especially in remote or hard to reach locations. PoE also promises to;

• Reduce deployment costs per device.

• Reduce the need for AC power adaptors.

• Simplify installation by letting customers employ a single CAT5e/ CAT6/ CAT6a cable for both data and power delivery.

• Offer customers centralized power backup and management.

• Make it possible to re-purpose copper from legacy phone networks.

• Enable moving PoE devices without the network seeing any down time.

Energy saving is a big part of PoE in particular, but the standard is really focused on energy efficiency as it uses all 4 pairs of wires in Ethernet cabling whereas previous versions of the standard used only two. The latest standard maintains a power-signature level that supports lighting or IoT applications to be powered with PoE and have acceptable standby performance when needed.

Another benefit, is that PoE in combination with analytics software can let facilities-management teams determine what areas of buildings are unoccupied and save electricity by remotely turning off lights and HVAC devices.

An important and growing benefit of PoE is in deploying WiFi access points. These devices are often placed in locations where it would be difficult to extend traditional electric lines, such as behind ceiling panels. The growth of wireless in buildings, offices and places like sports arenas fuels the need for PoE as it makes wireless roll-outs so much more tangible and easier to deploy.

3) Active PoE

802.3af/at (PoE/PoE+) | 802.3bt (PoE++)

Active PoE provides a safe alternative to passive PoE. When a device is plugged into an Active PoE switch, the product and the power source first perform a 'handshake' to ensure the device can accept the voltage being supplied by the switch or injector. This makes active PoE the safer PoE option for office or home environments where people may accidentally plug a computer into the PoE switch.

With active PoE, there are a variety of options available ranging from 15W - 100W, to power even the most power intensive equipment.

802.3af (PoE) supports a maximum of 15.4W.

Suited to low power devices such as VoIP phones or home WiFi access points and is the most commonly used Active PoE. 802.3af PoE uses 4/8 strands of the Ethernet cable in either a Midspan (Mode A) or Endspan (Mode B) configuration. This provides a 10/100Mbps (Fast Ethernet) data and power transmission. When using Gigabit PoE, depending on the manufacturer, either 4 or all 8 strands are used for data and power transmission.

802.3at (PoE+) supports a maximum of 30W.

802.3at offers a higher wattage than 802.3af and is therefore ideal for more power-hungry devices such as a PTZ camera or high power access point. Pictured below is the Ubiquiti UniFi UAP-AC-EDU which requires maximum power consumption over 802.3at. This WiFi access point also incorporates a built-in loudspeaker for community/ public broadcasting.

802.3bt (PoE++) supports a maximum of 60W on Type 3 and 100W on Type 4.

802.3bt is the latest commercial standard that utilizes all 8 strands of the Ethernet cable for power and data. This feature makes provision for higher power requirements and Gigabit data connections. Aside from single products, a common use for 802.3bt would be to provide high wattage to a single unit such as the Ubiquiti UniFi US-5-FLEX switch (pictured below) and have that device provide PoE passthrough to multiple units with smaller power requirements such as IP cameras, VoIP telephony appliances and WiFi access points.

Another single product from the Ubiquiti UniFi stable that requires PoE++ power delivery would be the UniFi BaseStation XG, pictured below. This unit will only power-up and operate over the IEEE 802.3++ standard due to its extremely high power demands.

The various forms of Active and Passive PoE utilize the individual cores of the Ethernet cable differently to provide power to your appliances.

Active PoE injectors and switches either support Mode A, Mode B or both, depending on the manufacturer. The mode supported determines which strands of the cable are used for power and data. If you are having trouble powering a device, check the mode supported by your device and ensure your PoE switch or injector supports the correct mode.

4) Auto-sensing PoE

Many PoE switches offer both passive and active PoE, rolled into a single product. Items such as the Ubiquiti UniFi US-XG-6POE switch, pictured below, offer both 24V passive PoE as well as 48v 802.3af/at PoE. Once connected, the switch will perform the 'handshake' with the device and determine what power is required. Once it has determined the appliance capabilities, it will commence with supplying power.

Some switches provide both 24V passive and 48v 802.3af/at but do not offer auto-sensing technology. These switches require the user to log into the switch and select the required voltage for each individual port on the switch. A good example of a switch that operates in this manner is the Ubiquiti UniFi US-8-150W, pictured below.

As can be seen in the below image, the US-8-150W has an individual configuration tab, labelled 'Ports'. From here, the administrator can setup their PoE requirements as required per individual switching port.

5) Passive PoE

Passive PoE is a simple alternative to active PoE. However, it does not have any of the built-in safeguards. Passive PoE accepts a wide voltage range but leaves the door open for possible damage to products not supporting PoE, or over-voltage when the incorrect power supply is used. With Passive PoE there is no 'handshake' and the PoE injector or switch simply supplies power to any device connected.

6) PoE Splitter

PoE splitters offer a simple 'hack' to power non-compliant devices via PoE. A splitter is made up of two components, an injector and a splitter. The injector accepts the power and data and combines them over the Ethernet cable. When reaching the non-compliant device, the splitter then 'splits' the power and data into two separate connectors. A DC jack for power, and an RJ45-male for data. The diagram below shows a simple PoE splitter setup.

7) PoE Detector

The Power over Ethernet (PoE) Detector, connected to an RJ-45 outlet, tests the cabling infrastructure for the presence of power, either IEEE 802.3af or IEEE 802.3at standard compliant. The PoE Detector identifies the existence and type of Power Sourcing Equipment, or 'PSE' (either Endspan or Midspan) in your network.