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Chapter 8
Power Over Ethernet
Overview
What is PoE?
Based on the global standard IEEE 802.3af, PoE is a technology for wired
Ethernet, the most widely installed local area network technology adopted today.
PoE allows the electrical power necessary for the operation of each end-device
to be carried by data cables rather than by separate power cords. New network
applications, such as IP Cameras, VoIP Phones, and Wireless Networking, can
help enterprises improve productivity. It minimizes wires that must be used to
install the network for offering lower cost, and less power failures.
IEEE802.3af also called Data Terminal equipment (DTE) power via Media
dependent interface (MDI) is an international standard to define the transmission
for power over Ethernet. The 802.3af is delivering 48V power over RJ-45 wiring.
Besides 802.3af also define two types of source equipment: Mid-Span and End-
Span.
Mid-Span
Mid-Span device is placed between legacy switch and the powered device. Mid-
Span is tap the unused wire pairs 4/5 and 7/8 to carry power, the other four is for
data transmit.
End-Span
End-Span device is direct connecting with power device. End-Span could also
tap the wire 1/2 and 3/6.
GE-DS-242-PoE Managed Ethernet Switch User Manual
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