As knowledge of PoE’s capabilities and benefits as spread, more and more system operators have taken advantage of PoE technology. However, the IEEE 802.3af standard has a few limitations that make 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 standardized PoE devices. This white paper will identify the key additional advantages offered by PoE Plus and explore the enormous potential of this new technology in scenarios that previously could not take advantage of PoE
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 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:
Low-power IP cameras are well-served by existing 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 ruggedized for operations outdoors, especially in harsh conditions, also need more power in order to use their heating units. It would be nice to be able to use 802.3af PoE technology to supply power to each outdoor camera, but 802.3af just isn’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 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 RFs, 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 802.3af-compliant PSEs is too weak to offer a viable alternative to conventional power sourcing.
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 802.3af, classification on the hardware layer (Layer 1) was optional. In 802.3at, this identification is mandatory. What’s more, 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 more power 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 previously off-limits for PoE have come into play. Outdoor applications that make heavy use of ruggedized, 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 maximize their efficiency.
PoE Plus in Action: One Deployment Scenario Intelligent Traffic System (ITS): Intelligent traffic management and video surveillance has emerged as a popular program for many local municipalities. Traffic cameras, sensors, intelligent lights, and embedded computers are often deployed along freeways and roads in order to monitor and improve traffic safety. This means the cameras will be exposed to the elements, and deployed at remote locations. 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 perfect backbone for ITS networks. Long-distance fibre gives 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