What is Power-over-Ethernet (PoE)?
2017-10-06
PoE Definition
Short for Power over Ethernet, PoE is a standard that allows Ethernet cables to simultaneously transmit data and power using a single network cable. This allows system integrators and network installers to deploy powered devices in locations that lack electrical circuitry. PoE eliminates the expense of installing additional electrical wiring which entails hiring professional electrical installers to ensure that strict conduit regulations are followed. Typical PoE users are businesses adding to their network or adding VoIP phones in buildings where new power lines would be expensive or inconvenient.

What are the advantages of Power over Ethernet?
Cost savings– PoE significantly reduces the need for electricians to install conduit, electrical wiring, and outlets throughout the enterprise.   With PoE, only one cable – a simple CAT-5 Ethernet – is required.
Quick Deployment– PoE simply requires plugging in networking cabling to the proper equipment in order to function correctly.
Flexibility– Network administrators can deploy powered devices at nearly any location. Shielded cabling can be used for outdoor environments. Industrial-grade powered devices can be used for industrial environments.
Safety– Because PoE utilizes a relatively low voltage, it presents low risks of electrical hazards.
Reliability– PoE falls under IEEE’s strict 802.3 standard umbrage.
Scalability– PoE makes it simple to add new equipment to a network.

PoE Applications
VoIP phones
IP cameras
Wireless Access Points
PoE lighting
ATM machines
IP Intercoms
Security Card Readers
IP Clocks
Vending Machines

802.3af and 802.3at PoE Standards
There are currently two PoE standards available. The 802.3af standard supports 15.44 watts of power. But even though 802.3af Powered Sourcing Equipment (PSE) are able to transmit 15.44 watts of power, powered devices (PDs) can only reliably receive 12.95 watts of power due to power dissipation. In 2009, IEEE introduced the higher powered 802.3at standard, also known as PoE+. The standard supports 30 watts of power, but in a similar fashion to the 802.3af standard, power dissipation causes powered devices to receive slightly lower amounts of power, specifically 25.5 watts of power.

IEEE is currently overseeing yet another higher powered PoE standard. As the utility of PoE expands beyond the networking sector, higher powered PoE will be able to support nurse call systems, the point of sale systems, IP turrets used by financial traders, and higher powered IP cameras such as PTZ Cameras, among many other applications. 802.3bt, also known as PoE++, the new standard is expected to be ratified in early 2017, will utilize all four twisted pairs to transmit power. The 802.3bt standard will be able to achieve 49-70 watts of power using this method. The new standard will essentially combine both Mode A and Mode B to achieve the higher voltage. Some sources even site that the standard will be able to supply up to 100 watts of DC power. This newer standard will not only allow for higher power but will also be able to support 10 Gbps connections. Type A specifies for 60W (50 watts of power) and Type B specifies for about 100 watts of power (approximately 80 watts of power with power dissipation).
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