The latest developments in PoE technology: PoE Plus

An industry-wide Power over Ethernet standard was officially ratified in 2003 with IEEE 802.3af, and since then the use of Power over Ethernet technology has rapidly grown around the world in many industries and applications.

According to the report ‘Power over Ethernet, Global Market Opportunity Analysis’, which was conducted by VDC Research in 2008, communications and industrial IT analysts estimate that, by 2012, one quarter of all of the ethernet ports in use around the world will be Power over Ethernet (PoE) capable.

As the knowledge of PoE’s capabilities and benefits spreads, more and more system operators took advantage of this technology. However, it was found that the IEEE 802.3af standard had a few limitations that made it unsuitable for certain demanding applications. In response, the IEEE 802.3at standard, also known as ‘PoE Plus’, was ratified to further expand the scope and capabilities of standardised PoE devices.

This article will endeavour to identify the key additional advantages that are offered by the PoE Plus standard, as well as explore the enormous potential of this new technology in scenarios that previously could not take advantage of PoE technology.

PoE: a brief history

Ethernet technology has been used for decades and ethernet cables can now be found in enterprise offices, residential homes and industrial automation applications, to name a few. In most of these systems, the ethernet cabling has been found to be installed almost everywhere throughout the premises, so one could naturally conclude that it would be more efficient if this cabling could deliver both data and power, instead of requiring additional power cabling to be installed. By completely eliminating the need to find a local power supply for each of the ethernet-connected devices, this would dramatically expand the device-deployment flexibility and eliminate the costs associated with added power cabling.

The PoE idea was so promising that many vendors, such as Cisco, 3Com and Intel developed their own proprietary PoE technologies. Users who adopted proprietary solutions were on the ‘bleeding edge’ of technology. While they enjoyed the benefits of PoE technology, they also needed to deal with countless headaches such as interoperability and compatibility issues, vendor lock-in and inconsistent support.

The fact that these proprietary solutions were used at all, despite their many hazards, testifies to the fundamental usefulness of PoE technology.

Fortunately, in 1999 the IEEE began to work on a PoE standard, which was finalised in 2003 with IEEE 802.3af. With standardised, documented and widely available products based on this technology, PoE truly took off. The technology could supply power to devices in locations where it was previously difficult, if not impossible, to deliver power. Examples of such devices include remote network switches, security cameras and outdoor wireless LAN access points.

Emerging limitations of IEEE 802.3af

IEEE 802.3af was a great start, but many ethernet-connected devices simply needed more power. As useful as PoE has proven to be, it has become clear that the IEEE 802.3af standard falls short when it comes to certain demanding scenarios. Power sourcing equipment (PSE) with IEEE 802.3af PoE technology can only provide a maximum of 15.4 W of power to powered devices (PD). There are many ethernet-connected devices, such as the following, that simply need more power:

• PTZ/outdoor CCTV cameras: Low-power IP cameras are well served by existing IEEE 802.3af PoE technology. However, cameras with pan, tilt, zoom (PTZ) functionality are increasingly popular, and these cameras use more power in order to operate their motors. Cameras that are ruggedised for operations outdoors, especially in harsh conditions, also need more power in order to use their heating units. It would be far more efficient to be able to use IEEE 802.3af PoE technology to supply power to each outdoor camera, but IEEE 802.3af specifications just weren’t up to the task of providing enough power for these devices.
• LED display boards: Ethernet-connected LED display boards display up-to-date messages from the network. These display boards use bright light-emitting diodes, which demand substantially more power than the 15.4 W available over an IEEE 802.3af PoE line.
• Long-distance LAN devices: Basic wireless access points can get by with 15.4 W of power. However, high-performance wireless devices that provide wider coverage use high gain antennas and multiple frequencies, all of which demand much more power. These high-powered wireless devices are particularly common in widely distributed, remote applications. This is precisely the type of application where power supplies and cables are a major cost - yet the power supplied by IEEE 802.3af-compliant PSEs is too weak to offer a viable alternative to conventional power sourcing.

How PoE Plus transforms PoE applications

In September 2009, the IEEE organisation ratified IEEE 802.3at (‘PoE Plus’), which dramatically improved PoE’s ability to meet the requirements of more demanding applications. With PoE Plus, it is possible to use just an ethernet cable to deliver power to more power-hungry devices.

PoE Plus offers the following key advantages over conventional PoE:

• More powerful: IEEE 802.3at technology increases the power delivered to PDs to 34.2 W, which is nearly double the power delivered by the old PoE technology. With this extra power, it is possible to use an ethernet cable to deliver power to devices such as outdoor cameras, LED display boards, WiMAX devices, and even some embedded computers or terminal computers. This capability alone unlocks the possibility of using PoE in applications that were previously too demanding for PoE technology.
• More efficient: PoE Plus is not only more powerful, it is also more efficient. IEEE 802.3at defines a new method of communication and identification between PSEs and PDs. In IEEE 802.3af, classification on the hardware layer (Layer 1) was optional. In 802.3at, this identification is mandatory. What’s more, IEEE 802.3at adds an additional data-layer (Layer 2) classification mechanism, known as the Link Layer Discovery Protocol (LLDP). LLDP allows the PSE to repeatedly request status information from the PD and dynamically allocate power in response. This means that PDs will use power more efficiently and only request maximum power when it is needed. Power efficiency is particularly useful for applications that must be frugal in their power consumption, such as remote applications powered by batteries or solar cells. However, less power consumption will translate into an improved bottom line no matter the application, simply by reducing the power bill.

Now that PoE Plus is available, entire categories of applications that were previously ‘off limits’ for PoE have come into play. Outdoor applications that make heavy use of ruggedised, power-consuming devices can now leverage PoE technology.

Applications with limited power resources, such as those powered by battery or solar cells, can now exploit PoE’s advanced power allocation mechanisms to maximise their efficiency.

PoE Plus in action: one deployment scenario

The combination of intelligent traffic management systems (ITS) with video surveillance technologies has emerged as a popular program for many local municipalities around the world. Traffic cameras, sensors, intelligent lights and embedded computers are often deployed along freeways and roads in order to monitor and improve the flow and safety of traffic. Being a largely outdoor application means the cameras will be exposed to the elements and deployed at remote locations. As a result, the cameras would need a wide operating temperature range in order to work reliably in this operating environment.

Robust gigabit ethernet infrastructures with PoE Plus support are the ideal backbone for ITS networks, and long-distance optical fibres give the network enough range to cover the entire traffic grid.

Meanwhile, PoE technology allows devices to be deployed anywhere ethernet cables go, even if a power supply is not available. Using PoE technology also completely eliminates the extra cost of power supplies and power cables.

A complete intelligent traffic system integrates cameras, lights, embedded computers and sensors - all of which can be powered with PoE Plus. The extra power supplied by PoE Plus allows municipal authorities to deploy cameras even where conditions are severe enough to require highly ruggedised self-heating camera units; and that makes it possible to deploy PTZ cameras in high-traffic locations.

PoE Plus also offers enough power to supply local intelligence and front-end control in the form of embedded computers. With this flexibility, systems can perform advanced automated actions such as triggering a camera’s zoom function when a car runs a red light.

Finally, with LLDP communications maximising the power efficiency of all the PDs in this network, the entire system will consume less electricity.

IEEE802.3at takes PoE to new places. While PoE has created systems that were efficient, reliable, safe and easy to maintain, now that PoE Plus is available, PoE is a viable option for even more applications than before.

Table 1: PoE and PoE Plus at a glance.

By Alvis Chen, Product Manager, Moxa Inc.