Overview

Power over Ethernet or PoE technology describes a system to safely transfer electrical power, along with data, to remote devices over standard category 5 cable in an Ethernet network. It does not require modification of existing Ethernet cabling infrastructure. The IEEE 802.3af PoE standard provides up to 15.4 W of DC power (minimum 44 VDC and 350 mA) to each device. Only 12.95 W is assured to be available at the powered device as some power is dissipated in the cable.

The IEEE 802.3at PoE standard (ratified September 11, 2009), provides up to 25W of power. Some vendors have announced products that claim to comply with the new 802.3at standard and offer up to 51W of power over a single cable by utilizing twice the pairs in the cable. Numerous non-standard schemes had been used prior to PoE standardization to provide power over Ethernet cabling. Some are still in active use.

 
What is PD and PSE?

Power Over Ethernet, IEEE802.3af, is constructed by Power Sourcing Equipment (PSE) and Power Device (PD). IEEE802.3at is the advanced high power POE solution, so it is called POE+. It supports PSE output power up to 30 watt and 4 pairs deliver 48V DC to PD. POE+ can provide up to 60 watt at the output of PSE when uses two PSE channels on a single RJ45 and applies 48V DC on 4 pairs simultaneously.

 

In/Out

protocol

Application

PD
Power Device

Power Input
from Ethernet(RJ45)

Input

POE 802.3 AF(15.4W)

Up to W10.1"LED Panel
with I930

(Use POE 802.3 AT)

POE 802.3 AT(30W)

PSE
Power Supply Equipment

Power Output
from Ethernet(RJ45)

Output

POE 802.3 AF(15.4W)

All Products with I930

POE 802.3 AT(30W)

  Benefits:
  • Cost Saving
  • 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. Estimates of cost savings using PoE range from $500 to $1,000 per port. In larger settings, this represents a major cost reduction.

  • Flexibility
  • A PoE appliance or device can be located anywhere without the need for AC outlets. For example, wireless LAN access points can be located – and relocated – on or near ceilings, to fine tune optimum RF reception. For example, customers often find that access points are more effective on the ceiling, out of reach from an AC outlet.

  • Reliability
  • Because PoE networks have fewer wires, there is less likelihood of an inadvertent power disruption (accidental shut off, etc). With an Uninterrupted Power Supply (UPS) power to the devices is assured during a power failure.

  • Network Control
  • Using SNMP, network administrators can monitor and control powered devices, including resetting or shut-off. This allows increased security, as devices can be powered down when not in use, or if there is unauthorized access.

  • Safety
  • Power mains are eliminated. Since only 48v DC is used, PoE conforms to Underwriter's Laboratories (UL) Safety Extra Low Voltage (SELV) classification.

      

          

     

     
     
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