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6. POWER OVER
Based on the global standard IEEE 802.3af, PoE is a technology
netw
carri
and Wireless Networking, can help enterprises improve productivity. It minimizes wires that must be used to install the
netw rk for offering lower cost, and less power failures.
alled Data Terminal equipment (DTE) power via Media dependent interface (MDI) is an international
stan
side
n legacy switch and the powered device. Mid-Span is tap the unused wire pairs 4/5
PoE
The specification of PoE typically requires two devices: the Powered Source Equipment (PSE) and the Powered Device
an or a Mid-Span, while the PD is a PoE-enabled terminal, such as IP Phones, Wireless
LAN, etc. Power can be delivered over data pairs or spare pairs of standard CAT-5 cabling.
How
A sta
spec
The
the p
to be used).
ETHERNET OVERVIEW
What is PoE?
for wired Ethernet, the most widely installed local area
ork technology adopted today. PoE allows the electrical power necessary for the operation of each end-device to be
ed by data cables rather than by separate power cords. New network applications, such as IP Cameras, VoIP Phones,
o
IEEE802.3af also c
dard to define the transmission for power over Ethernet. The 802.3af is delivering 48V power over RJ-45 wiring. Be-
s 802.3af also define two types of source equipment: Mid-Span and End-Span.
Mid-Span
Mid-Span device is placed betwee
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.
System Architecture
(PD). The PSE is either an End-Sp
Power is Transferred Through the Cable
ndard CAT5 Ethernet cable has four twisted pairs, but only two of these are used for 10BASE-T and 100BASE-T. The
ification allows two options for using these cables for power, shown in Figure 2 and Figure 3:
spare pairs are used. Figure 2 shows the pair on pins 4 and 5 connected together and forming the positive supply, and
air on pins 7 and 8 connected and forming the negative supply. (In fact, a late change to the spec allows either polarity
Figure 1 - Power Supplied over the Spare Pins