<s>
Power	B-Device
over	I-Device
Ethernet	I-Device
,	O
or	O
PoE	B-Device
,	O
describes	O
any	O
of	O
several	O
standards	O
or	O
ad	O
hoc	O
systems	O
that	O
pass	O
electric	O
power	O
along	O
with	O
data	O
on	O
twisted-pair	B-Protocol
Ethernet	I-Protocol
cabling	O
.	O
</s>
<s>
This	O
allows	O
a	O
single	O
cable	O
to	O
provide	O
both	O
a	O
data	O
connection	O
and	O
enough	O
electricity	O
to	O
power	O
devices	O
such	O
as	O
wireless	B-Device
access	I-Device
points	I-Device
(	O
WAPs	B-Device
)	O
,	O
Internet	O
Protocol	O
(	O
IP	O
)	O
cameras	O
and	O
voice	B-Application
over	I-Application
Internet	I-Application
Protocol	I-Application
(	O
VoIP	B-Application
)	O
phones	O
.	O
</s>
<s>
There	O
are	O
several	O
common	O
techniques	O
for	O
transmitting	O
power	B-Device
over	I-Device
Ethernet	I-Device
cabling	O
.	O
</s>
<s>
These	O
standards	O
are	O
known	O
as	O
alternative	B-Device
A	I-Device
,	O
alternative	B-Device
B	I-Device
,	O
and	O
4PPoE	B-Device
.	O
</s>
<s>
For	O
10BASE-T	B-Protocol
and	O
100BASE-TX	B-Protocol
,	O
only	O
two	O
of	O
the	O
four	O
signal	O
pairs	O
in	O
typical	O
Cat	O
5	O
cable	O
are	O
used	O
.	O
</s>
<s>
Alternative	B-Device
B	I-Device
separates	O
the	O
data	O
and	O
the	O
power	O
conductors	O
,	O
making	O
troubleshooting	O
easier	O
.	O
</s>
<s>
Alternative	B-Device
A	I-Device
transports	O
power	O
on	O
the	O
same	O
wires	O
as	O
data	O
for	O
10	O
and	O
100Mbit/s	O
Ethernet	O
variants	O
.	O
</s>
<s>
This	O
is	O
similar	O
to	O
the	O
phantom	B-Algorithm
power	I-Algorithm
technique	O
commonly	O
used	O
for	O
powering	O
condenser	O
microphones	O
.	O
</s>
<s>
Because	O
twisted-pair	B-Protocol
Ethernet	I-Protocol
uses	O
differential	O
signaling	O
,	O
this	O
does	O
not	O
interfere	O
with	O
data	O
transmission	O
.	O
</s>
<s>
4PPoE	B-Device
provides	O
power	O
using	O
all	O
four	O
pairs	O
of	O
a	O
twisted-pair	O
cable	O
.	O
</s>
<s>
This	O
enables	O
higher	O
power	O
for	O
applications	O
like	O
pan	B-Algorithm
–	I-Algorithm
tilt	I-Algorithm
–	I-Algorithm
zoom	I-Algorithm
cameras	I-Algorithm
(	O
PTZ	O
)	O
,	O
high-performance	O
WAPs	B-Device
,	O
or	O
even	O
charging	O
laptop	O
batteries	O
.	O
</s>
<s>
In	O
addition	O
to	O
standardizing	O
existing	O
practice	O
for	O
spare-pair	O
(	O
Alternative	B-Device
B	I-Device
)	O
,	O
common-mode	O
data	O
pair	O
power	O
(	O
Alternative	B-Device
A	I-Device
)	O
and	O
4-pair	O
transmission	O
(	O
4PPoE	B-Device
)	O
,	O
the	O
IEEE	O
PoE	B-Device
standards	O
provide	O
for	O
signaling	O
between	O
the	O
power	O
sourcing	O
equipment	O
(	O
PSE	B-Device
)	O
and	O
powered	B-Device
device	I-Device
(	O
PD	B-Device
)	O
.	O
</s>
<s>
The	O
original	O
IEEE	B-Device
802.3af-2003	I-Device
PoE	B-Device
standard	O
provides	O
up	O
to	O
15.4W	O
of	O
DC	O
power	O
(	O
minimum	O
and	O
350mA	O
)	O
on	O
each	O
port	O
.	O
</s>
<s>
Only	O
12.95W	O
is	O
assured	O
to	O
be	O
available	O
at	O
the	O
powered	B-Device
device	I-Device
as	O
some	O
power	O
dissipates	O
in	O
the	O
cable	O
.	O
</s>
<s>
The	O
updated	O
IEEE	B-Device
802.3at-2009	I-Device
PoE	B-Device
standard	O
also	O
known	O
as	O
PoE+	B-Device
or	O
PoE	B-Device
plus	O
,	O
provides	O
up	O
to	O
25.5W	O
of	O
power	O
for	O
Type2	O
devices	O
.	O
</s>
<s>
The	O
2009	O
standard	O
prohibits	O
a	O
powered	B-Device
device	I-Device
from	O
using	O
all	O
four	O
pairs	O
for	O
power	O
.	O
</s>
<s>
The	O
IEEE	B-Device
802.3bt-2018	I-Device
standard	O
further	O
expands	O
the	O
power	O
capabilities	O
of	O
802.3at	B-Device
.	O
</s>
<s>
It	O
is	O
also	O
known	O
as	O
PoE++	B-Device
or	O
4PPoE	B-Device
.	O
</s>
<s>
This	O
development	O
opens	O
the	O
door	O
to	O
new	O
applications	O
and	O
expands	O
the	O
use	O
of	O
applications	O
such	O
as	O
high-performance	O
wireless	B-Device
access	I-Device
points	I-Device
and	O
surveillance	O
cameras	O
.	O
</s>
<s>
PoDL	O
initially	O
defined	O
ten	O
power	O
classes	O
,	O
ranging	O
from	O
0.5	O
to	O
50W	O
(	O
at	O
PD	B-Device
)	O
.	O
</s>
<s>
Examples	O
of	O
devices	O
powered	O
by	O
PoE	B-Device
include	O
:	O
</s>
<s>
A	O
mini	O
network	B-Protocol
switch	I-Protocol
installed	O
in	O
distant	O
rooms	O
,	O
to	O
support	O
a	O
small	O
cluster	O
of	O
Ethernet	O
ports	O
from	O
one	O
uplink	B-Application
cable	O
.	O
</s>
<s>
PoE	B-Device
power	O
is	O
fed	O
into	O
the	O
PD	B-Device
(	O
or	O
PoE	B-Device
in	O
)	O
port	O
.	O
</s>
<s>
These	O
switches	O
may	O
in	O
turn	O
power	O
remote	O
PoE	B-Device
devices	O
using	O
PoE	B-Device
pass	O
through	O
.	O
</s>
<s>
PoE	B-Device
Splitters	I-Device
that	O
output	O
the	O
power	O
,	O
often	O
at	O
a	O
different	O
voltage	O
(	O
e.g.	O
</s>
<s>
Power	O
sourcing	O
equipment	O
(	O
PSE	B-Device
)	O
are	O
devices	O
that	O
provide	O
(	O
source	O
)	O
power	O
on	O
the	O
Ethernet	O
cable	O
.	O
</s>
<s>
This	O
device	O
may	O
be	O
a	O
network	B-Protocol
switch	I-Protocol
,	O
commonly	O
called	O
an	O
endspan	O
(	O
IEEE	B-Device
802.3af	I-Device
refers	O
to	O
it	O
as	O
endpoint	O
)	O
,	O
or	O
an	O
intermediary	O
device	O
between	O
a	O
non-PoE-capable	O
switch	O
and	O
a	O
PoE	B-Device
device	O
,	O
an	O
external	O
PoE	B-Device
injector	I-Device
,	O
called	O
a	O
midspan	O
device	O
.	O
</s>
<s>
A	O
powered	B-Device
device	I-Device
(	O
PD	B-Device
)	O
is	O
any	O
device	O
powered	O
by	O
PoE	B-Device
,	O
thus	O
consuming	O
energy	O
.	O
</s>
<s>
Examples	O
include	O
wireless	B-Device
access	I-Device
points	I-Device
,	O
VoIP	B-Device
phones	I-Device
,	O
and	O
IP	B-Algorithm
cameras	I-Algorithm
.	O
</s>
<s>
Many	O
powered	B-Device
devices	I-Device
have	O
an	O
auxiliary	O
power	O
connector	O
for	O
an	O
optional	O
external	O
power	O
supply	O
.	O
</s>
<s>
Depending	O
on	O
the	O
design	O
,	O
some	O
,	O
none	O
,	O
or	O
all	O
of	O
the	O
device	O
's	O
power	O
can	O
be	O
supplied	O
from	O
the	O
auxiliary	O
port	O
,	O
with	O
the	O
auxiliary	O
port	O
also	O
sometimes	O
acting	O
as	O
backup	O
power	O
in	O
case	O
PoE-supplied	O
power	O
fails	O
.	O
</s>
<s>
Advocates	O
of	O
PoE	B-Device
expect	O
PoE	B-Device
to	O
become	O
a	O
global	O
long	O
term	O
DC	O
power	O
cabling	O
standard	O
and	O
replace	O
a	O
multiplicity	O
of	O
individual	O
AC	O
adapters	O
,	O
which	O
cannot	O
be	O
easily	O
centrally	O
managed	O
.	O
</s>
<s>
Critics	O
of	O
this	O
approach	O
argue	O
that	O
PoE	B-Device
is	O
inherently	O
less	O
efficient	O
than	O
AC	O
power	O
due	O
to	O
the	O
lower	O
voltage	O
,	O
and	O
this	O
is	O
made	O
worse	O
by	O
the	O
thin	O
conductors	O
of	O
Ethernet	O
.	O
</s>
<s>
Advocates	O
of	O
PoE	B-Device
,	O
like	O
the	O
Ethernet	B-Protocol
Alliance	I-Protocol
,	O
point	O
out	O
that	O
quoted	O
losses	O
are	O
for	O
worst	O
case	O
scenarios	O
in	O
terms	O
of	O
cable	O
quality	O
,	O
length	O
and	O
power	O
consumption	O
by	O
powered	B-Device
devices	I-Device
.	O
</s>
<s>
In	O
any	O
case	O
,	O
where	O
the	O
central	O
PoE	B-Device
supply	O
replaces	O
several	O
dedicated	O
AC	O
circuits	O
,	O
transformers	O
and	O
inverters	O
,	O
the	O
power	O
loss	O
in	O
cabling	O
can	O
be	O
justifiable	O
.	O
</s>
<s>
The	O
integration	O
of	O
PoE	B-Device
with	O
the	O
IEEE	O
802.3az	O
Energy-Efficient	O
Ethernet	O
(	O
EEE	O
)	O
standard	O
potentially	O
produces	O
additional	O
energy	O
savings	O
.	O
</s>
<s>
Pre-standard	O
integrations	O
of	O
EEE	O
and	O
PoE	B-Device
(	O
such	O
as	O
Marvell	O
's	O
EEPoE	O
outlined	O
in	O
a	O
May	O
2011	O
white	O
paper	O
)	O
claim	O
to	O
achieve	O
a	O
savings	O
upwards	O
of	O
3W	O
per	O
link	O
.	O
</s>
<s>
Standards-based	O
Power	B-Device
over	I-Device
Ethernet	I-Device
is	O
implemented	O
following	O
the	O
specifications	O
in	O
IEEE	B-Device
802.3af-2003	I-Device
(	O
which	O
was	O
later	O
incorporated	O
as	O
clause	O
33	O
into	O
IEEE	O
802.3-2005	O
)	O
or	O
the	O
2009	O
update	O
,	O
IEEE	B-Device
802.3at	I-Device
.	O
</s>
<s>
The	O
standards	O
require	O
category	B-Protocol
5	I-Protocol
cable	I-Protocol
or	O
better	O
for	O
high	O
power	O
levels	O
but	O
allow	O
using	O
category	B-Protocol
3	I-Protocol
cable	I-Protocol
if	O
less	O
power	O
is	O
required	O
.	O
</s>
<s>
Power	O
is	O
supplied	O
as	O
a	O
common-mode	O
signal	O
over	O
two	O
or	O
more	O
of	O
the	O
differential	O
pairs	O
of	O
wires	O
found	O
in	O
the	O
Ethernet	O
cables	O
and	O
comes	O
from	O
a	O
power	O
supply	O
within	O
a	O
PoE-enabled	O
networking	O
device	O
such	O
as	O
an	O
Ethernet	B-Protocol
switch	I-Protocol
or	O
can	O
be	O
injected	O
into	O
a	O
cable	O
run	O
with	O
a	O
midspan	O
power	O
supply	O
,	O
an	O
additional	O
PoE	B-Device
power	O
source	O
that	O
can	O
be	O
used	O
in	O
combination	O
with	O
a	O
non-PoE	O
switch	O
.	O
</s>
<s>
A	O
phantom	B-Algorithm
power	I-Algorithm
technique	O
is	O
used	O
to	O
allow	O
the	O
powered	O
pairs	O
to	O
also	O
carry	O
data	O
.	O
</s>
<s>
This	O
permits	O
its	O
use	O
not	O
only	O
with	O
10BASE-T	B-Protocol
and	O
100BASE-TX	B-Protocol
,	O
which	O
use	O
only	O
two	O
of	O
the	O
four	O
pairs	O
in	O
the	O
cable	O
,	O
but	O
also	O
with	O
1000BASE-T	O
(	O
gigabit	O
Ethernet	O
)	O
,	O
2.5GBASE-T	O
,	O
5GBASE-T	O
,	O
and	O
10GBASE-T	O
which	O
use	O
all	O
four	O
pairs	O
for	O
data	O
transmission	O
.	O
</s>
<s>
This	O
is	O
possible	O
because	O
all	O
versions	O
of	O
Ethernet	B-Protocol
over	I-Protocol
twisted	I-Protocol
pair	I-Protocol
cable	O
specify	O
differential	O
data	O
transmission	O
over	O
each	O
pair	O
with	O
transformer	B-Device
coupling	I-Device
;	O
the	O
DC	O
supply	O
and	O
load	O
connections	O
can	O
be	O
made	O
to	O
the	O
transformer	O
center-taps	O
at	O
each	O
end	O
.	O
</s>
<s>
The	O
polarity	O
of	O
the	O
DC	O
supply	O
may	O
be	O
inverted	O
by	O
crossover	B-Protocol
cables	I-Protocol
;	O
the	O
powered	B-Device
device	I-Device
must	O
operate	O
with	O
either	O
pair	O
:	O
spare	O
pairs	O
4	O
–	O
5	O
and	O
7	O
–	O
8	O
or	O
data	O
pairs	O
1	O
–	O
2	O
and	O
3	O
–	O
6	O
.	O
</s>
<s>
+Comparison	O
of	O
PoE	B-Device
parameters	O
Property	O
802.3af	B-Device
,	O
PoE	B-Device
,	O
PoE+	B-Device
,	O
4PPoE	B-Device
or	O
PoE++	B-Device
,	O
4PPoE	B-Device
or	O
PoE++	B-Device
Power	O
available	O
at	O
PDMost	O
switched-mode	O
power	O
supplies	O
within	O
the	O
powered	B-Device
device	I-Device
will	O
lose	O
another	O
10	O
to	O
25%	O
of	O
the	O
available	O
power	O
to	O
heat	O
.	O
</s>
<s>
Maximum	O
power	O
delivered	O
by	O
PSE	B-Device
ISO/IEC	O
60950	O
Safety	O
Extra	O
Low	O
Voltage	O
(	O
SELV	O
)	O
standard	O
limits	O
power	O
to	O
100	O
W	O
per	O
port	O
(	O
similar	O
to	O
US	O
NEC	O
class	O
2	O
circuit	O
)	O
.	O
</s>
<s>
Voltage	O
range	O
(	O
at	O
PSE	B-Device
)	O
IEEE	B-Device
802.3at-2009	I-Device
Table	O
33-11	O
Voltage	O
range	O
(	O
at	O
PD	B-Device
)	O
IEEE	B-Device
802.3at-2009	I-Device
Table	O
33-18	O
IEEE	O
802.3bt	O
Table	O
145-1	O
Maximum	O
current	O
Imax	O
IEEE	B-Device
802.3at-2009	I-Device
Table	O
33-1	O
per	O
pair	O
per	O
pair	O
Maximum	O
cable	O
resistance	O
per	O
pairset	O
IEEE	B-Device
802.3at-2009	I-Device
33.1.4	O
Type	O
1	O
and	O
Type	O
2	O
system	O
parameters	O
(	O
Category	B-Protocol
3	I-Protocol
)	O
(	O
Category	B-Protocol
5	I-Protocol
)	O
Power	O
management	O
Three	O
power	O
class	O
levels	O
(	O
1-3	O
)	O
negotiated	O
by	O
signature	O
Four	O
power	O
class	O
levels	O
(	O
1-4	O
)	O
negotiated	O
by	O
signature	O
or	O
steps	O
negotiated	O
by	O
LLDP	B-Protocol
Six	O
power	O
class	O
levels	O
(	O
1-6	O
)	O
negotiated	O
by	O
signature	O
or	O
steps	O
negotiated	O
by	O
LLDPIEEE	O
802.3bt	O
145.3.1	O
PD	B-Device
Type	O
definitions	O
Eight	O
power	O
class	O
levels	O
(	O
1-8	O
)	O
negotiated	O
by	O
signature	O
or	O
steps	O
negotiated	O
by	O
LLDP	B-Protocol
Derating	O
of	O
maximum	O
cable	O
ambient	O
operating	O
temperature	O
None	O
with	O
one	O
mode	O
(	O
two	O
pairs	O
)	O
active	O
with	O
more	O
than	O
half	O
of	O
bundled	O
cables	O
pairs	O
at	O
ImaxIEEE	O
802.3bt	O
145.1.3.1	O
Cabling	O
requirements	O
with	O
temperature	O
planning	O
required	O
Supported	O
cabling	O
Category	B-Protocol
3	I-Protocol
and	O
Category	B-Protocol
5	I-Protocol
Category	O
5More	O
stringent	O
cable	O
specification	O
allows	O
assumption	O
of	O
more	O
current	O
carrying	O
capacity	O
and	O
lower	O
resistance	O
(	O
20.0	O
Ω	O
for	O
Category	B-Protocol
3	I-Protocol
versus	O
12.5	O
Ω	O
for	O
Category	B-Protocol
5	I-Protocol
)	O
.	O
</s>
<s>
Mode	O
A	O
delivers	O
power	O
on	O
the	O
data	O
pairs	O
of	O
100BASE-TX	B-Protocol
or	O
10BASE-T	B-Protocol
.	O
Mode	O
B	O
delivers	O
power	O
on	O
the	O
spare	O
pairs	O
.	O
</s>
<s>
PoE	B-Device
can	O
also	O
be	O
used	O
on	O
1000BASE-T	O
,	O
2.5GBASE-T	O
,	O
5GBASE-T	O
and	O
10GBASE-T	O
Ethernet	O
,	O
in	O
which	O
case	O
there	O
are	O
no	O
spare	O
pairs	O
and	O
all	O
power	O
is	O
delivered	O
using	O
the	O
phantom	O
technique	O
.	O
</s>
<s>
Mode	O
A	O
has	O
two	O
alternate	O
configurations	O
(	O
MDI	B-Protocol
and	O
MDI-X	B-Protocol
)	O
,	O
using	O
the	O
same	O
pairs	O
but	O
with	O
different	O
polarities	O
.	O
</s>
<s>
In	O
mode	O
A	O
,	O
pins	O
1	O
and	O
2	O
(	O
pair	O
#2	O
in	O
T568B	O
wiring	O
)	O
form	O
one	O
side	O
of	O
the	O
48V	B-Algorithm
DC	O
,	O
and	O
pins	O
3	O
and	O
6	O
(	O
pair	O
#3	O
in	O
T568B	O
)	O
form	O
the	O
other	O
side	O
.	O
</s>
<s>
These	O
are	O
the	O
same	O
two	O
pairs	O
used	O
for	O
data	O
transmission	O
in	O
10BASE-T	B-Protocol
and	O
100BASE-TX	B-Protocol
,	O
allowing	O
the	O
provision	O
of	O
both	O
power	O
and	O
data	O
over	O
only	O
two	O
pairs	O
in	O
such	O
networks	O
.	O
</s>
<s>
The	O
free	O
polarity	O
allows	O
PoE	B-Device
to	O
accommodate	O
for	O
crossover	B-Protocol
cables	I-Protocol
,	O
patch	O
cables	O
and	O
Auto	O
MDI-X	B-Protocol
.	O
</s>
<s>
In	O
mode	O
B	O
,	O
pins	O
4	O
–	O
5	O
(	O
pair	O
#1	O
in	O
both	O
T568A	O
and	O
T568B	O
)	O
form	O
one	O
side	O
of	O
the	O
DC	O
supply	O
and	O
pins	O
7	O
–	O
8	O
(	O
pair	O
#4	O
in	O
both	O
T568A	O
and	O
T568B	O
)	O
provide	O
the	O
return	O
;	O
these	O
are	O
the	O
"	O
spare	O
"	O
pairs	O
in	O
10BASE-T	B-Protocol
and	O
100BASE-TX	B-Protocol
.	O
</s>
<s>
The	O
PSE	B-Device
,	O
not	O
the	O
PD	B-Device
,	O
decides	O
whether	O
power	O
mode	O
A	O
or	O
B	O
shall	O
be	O
used	O
.	O
</s>
<s>
PDs	B-Device
that	O
implement	O
only	O
mode	O
A	O
or	O
mode	O
B	O
are	O
disallowed	O
by	O
the	O
standard	O
.	O
</s>
<s>
The	O
PSE	B-Device
can	O
implement	O
mode	O
A	O
or	O
B	O
or	O
both	O
.	O
</s>
<s>
A	O
PD	B-Device
indicates	O
that	O
it	O
is	O
standards-compliant	O
by	O
placing	O
a	O
25kΩ	O
resistor	O
between	O
the	O
powered	O
pairs	O
.	O
</s>
<s>
If	O
the	O
PSE	B-Device
detects	O
a	O
resistance	O
that	O
is	O
too	O
high	O
or	O
too	O
low	O
(	O
including	O
a	O
short	O
circuit	O
)	O
,	O
no	O
power	O
is	O
applied	O
.	O
</s>
<s>
This	O
protects	O
devices	O
that	O
do	O
not	O
support	O
PoE	B-Device
.	O
</s>
<s>
An	O
optional	O
power	O
class	O
feature	O
allows	O
the	O
PD	B-Device
to	O
indicate	O
its	O
power	O
requirements	O
by	O
changing	O
the	O
sense	O
resistance	O
at	O
higher	O
voltages	O
.	O
</s>
<s>
To	O
retain	O
power	O
,	O
the	O
PD	B-Device
must	O
use	O
at	O
least	O
5	O
–	O
10mA	O
for	O
at	O
least	O
60ms	O
at	O
a	O
time	O
.	O
</s>
<s>
If	O
the	O
PD	B-Device
goes	O
more	O
than	O
400ms	O
without	O
meeting	O
this	O
requirement	O
,	O
the	O
PSE	B-Device
will	O
consider	O
the	O
device	O
disconnected	O
and	O
,	O
for	O
safety	O
reasons	O
,	O
remove	O
power	O
.	O
</s>
<s>
There	O
are	O
two	O
types	O
of	O
PSEs	B-Device
:	O
endspans	O
and	O
midspans	O
.	O
</s>
<s>
Endspans	O
(	O
commonly	O
called	O
PoE	B-Device
switches	O
)	O
are	O
Ethernet	B-Protocol
switches	I-Protocol
that	O
include	O
the	O
power	B-Device
over	I-Device
Ethernet	I-Device
transmission	O
circuitry	O
.	O
</s>
<s>
Midspans	O
are	O
power	O
injectors	O
that	O
stand	O
between	O
a	O
regular	O
Ethernet	B-Protocol
switch	I-Protocol
and	O
the	O
powered	B-Device
device	I-Device
,	O
injecting	O
power	O
without	O
affecting	O
the	O
data	O
.	O
</s>
<s>
Endspans	O
are	O
normally	O
used	O
on	O
new	O
installations	O
or	O
when	O
the	O
switch	O
has	O
to	O
be	O
replaced	O
for	O
other	O
reasons	O
(	O
such	O
as	O
moving	O
from	O
10/100Mbit/s	O
to	O
1Gbit/s	O
)	O
,	O
which	O
makes	O
it	O
convenient	O
to	O
add	O
the	O
PoE	B-Device
capability	O
.	O
</s>
<s>
Midspans	O
are	O
used	O
when	O
there	O
is	O
no	O
desire	O
to	O
replace	O
and	O
configure	O
a	O
new	O
Ethernet	B-Protocol
switch	I-Protocol
,	O
and	O
only	O
PoE	B-Device
needs	O
to	O
be	O
added	O
to	O
the	O
network	O
.	O
</s>
<s>
+Stages	O
of	O
powering	O
up	O
a	O
PoE	B-Device
link	O
Stage	O
Action	O
Volts	O
specified	O
(	O
V	O
)	O
802.3af	B-Device
802.3at	B-Device
Detection	O
PSE	B-Device
detects	O
if	O
the	O
PD	B-Device
has	O
the	O
correct	O
signature	O
resistance	O
of	O
Classification	O
PSE	B-Device
detects	O
resistor	O
indicating	O
power	O
range	O
(	O
see	O
below	O
)	O
Signals	O
PSE	B-Device
is	O
802.3at	B-Device
capable	O
.	O
</s>
<s>
PD	B-Device
presents	O
a	O
load	O
.	O
</s>
<s>
—	O
PSE	B-Device
outputs	O
classification	O
voltage	O
again	O
to	O
indicate	O
802.3at	B-Device
capability	O
—	O
Signals	O
PSE	B-Device
is	O
802.3at	B-Device
capable	O
.	O
</s>
<s>
PD	B-Device
presents	O
a	O
load	O
.	O
</s>
<s>
IEEE	B-Device
802.3at	I-Device
capable	O
devices	O
are	O
also	O
referred	O
to	O
as	O
Type	O
2	O
.	O
</s>
<s>
An	O
802.3at	B-Device
PSE	B-Device
may	O
also	O
use	O
LLDP	B-Protocol
communication	O
to	O
signal	O
802.3at	B-Device
capability	O
.	O
</s>
<s>
Class	O
4	O
can	O
only	O
be	O
used	O
by	O
IEEE	B-Device
802.3at	I-Device
(	O
Type	O
2	O
)	O
devices	O
,	O
requiring	O
valid	O
Class	O
2	O
and	O
Mark	O
2	O
currents	O
for	O
the	O
power	O
up	O
stages	O
.	O
</s>
<s>
An	O
802.3af	B-Device
device	O
presenting	O
a	O
class	O
4	O
current	O
is	O
considered	O
non-compliant	O
and	O
,	O
instead	O
,	O
will	O
be	O
treated	O
as	O
a	O
Class	O
0	O
device	O
.	O
</s>
<s>
Link	B-Protocol
Layer	I-Protocol
Discovery	I-Protocol
Protocol	I-Protocol
(	O
LLDP	B-Protocol
)	O
is	O
a	O
layer-2	O
Ethernet	O
protocol	O
for	O
managing	O
devices	O
.	O
</s>
<s>
LLDP	B-Protocol
allows	O
an	O
exchange	O
of	O
information	O
between	O
a	O
PSE	B-Device
and	O
a	O
PD	B-Device
.	O
</s>
<s>
This	O
information	O
is	O
formatted	O
in	O
type	B-Protocol
–	I-Protocol
length	I-Protocol
–	I-Protocol
value	I-Protocol
(	O
TLV	O
)	O
format	O
.	O
</s>
<s>
PoE	B-Device
standards	O
define	O
TLV	O
structures	O
used	O
by	O
PSEs	B-Device
and	O
PDs	B-Device
to	O
signal	O
and	O
negotiate	O
available	O
power	O
.	O
</s>
<s>
PSE	B-Device
(	O
provider	O
)	O
tests	O
PD	B-Device
(	O
consumer	O
)	O
physically	O
using	O
802.3af	B-Device
phase	O
class	O
3	O
.	O
</s>
<s>
PSE	B-Device
powers	O
up	O
PD	B-Device
.	O
</s>
<s>
PD	B-Device
sends	O
to	O
PSE	B-Device
:	O
I	O
'm	O
a	O
PD	B-Device
,	O
max	O
power	O
=	O
X	O
,	O
max	O
power	O
requested	O
=	O
X	O
.	O
</s>
<s>
PSE	B-Device
sends	O
to	O
PD	B-Device
:	O
I	O
'm	O
a	O
PSE	B-Device
,	O
max	O
power	O
allowed	O
=	O
X	O
.	O
</s>
<s>
PD	B-Device
may	O
now	O
use	O
the	O
amount	O
of	O
power	O
as	O
specified	O
by	O
the	O
PSE	B-Device
.	O
</s>
<s>
Some	O
Cisco	O
WLAN	B-Device
access	I-Device
points	I-Device
and	O
VoIP	B-Device
phones	I-Device
supported	O
a	O
proprietary	O
form	O
of	O
PoE	B-Device
many	O
years	O
before	O
there	O
was	O
an	O
IEEE	O
standard	O
for	O
delivering	O
PoE	B-Device
.	O
</s>
<s>
Cisco	O
's	O
original	O
PoE	B-Device
implementation	O
is	O
not	O
software	O
upgradeable	O
to	O
the	O
IEEE	B-Device
802.3af	I-Device
standard	O
.	O
</s>
<s>
Cisco	O
's	O
original	O
PoE	B-Device
equipment	O
is	O
capable	O
of	O
delivering	O
up	O
to	O
per	O
port	O
.	O
</s>
<s>
The	O
amount	O
of	O
power	O
to	O
be	O
delivered	O
is	O
negotiated	O
between	O
the	O
endpoint	O
and	O
the	O
Cisco	O
switch	O
based	O
on	O
a	O
power	O
value	O
that	O
was	O
added	O
to	O
the	O
Cisco	O
proprietary	O
Cisco	B-Protocol
Discovery	I-Protocol
Protocol	I-Protocol
(	O
CDP	O
)	O
.	O
</s>
<s>
CDP	O
is	O
also	O
responsible	O
for	O
dynamically	O
communicating	O
the	O
Voice	O
VLAN	O
value	O
from	O
the	O
Cisco	O
switch	O
to	O
the	O
Cisco	O
VoIP	B-Device
Phone	I-Device
.	O
</s>
<s>
Under	O
Cisco	O
's	O
pre-standard	O
scheme	O
,	O
the	O
PSE	B-Device
(	O
switch	O
)	O
will	O
send	O
a	O
fast	O
link	O
pulse	O
(	O
FLP	O
)	O
on	O
the	O
transmit	O
pair	O
.	O
</s>
<s>
The	O
PD	B-Device
(	O
device	O
)	O
connects	O
the	O
transmit	O
line	O
to	O
the	O
receive	O
line	O
via	O
a	O
low-pass	B-Algorithm
filter	I-Algorithm
.	O
</s>
<s>
The	O
PSE	B-Device
gets	O
the	O
FLP	O
in	O
return	O
.	O
</s>
<s>
The	O
PSE	B-Device
will	O
provide	O
a	O
common	O
mode	O
current	O
between	O
pairs	O
1	O
and	O
2	O
,	O
resulting	O
in	O
and	O
default	O
of	O
allocated	O
power	O
.	O
</s>
<s>
The	O
PD	B-Device
must	O
then	O
provide	O
Ethernet	O
link	O
within	O
to	O
the	O
auto-negotiation	O
mode	O
switch	B-Protocol
port	I-Protocol
.	O
</s>
<s>
A	O
later	O
CDP	O
message	O
with	O
a	O
TLV	O
tells	O
the	O
PSE	B-Device
its	O
final	O
power	O
requirement	O
.	O
</s>
<s>
In	O
2014	O
,	O
Cisco	O
created	O
another	O
non-standard	O
PoE	B-Device
implementation	O
called	O
(	O
UPOE	O
)	O
.	O
</s>
<s>
A	O
proprietary	O
high-power	O
development	O
called	O
LTPoE++	O
,	O
using	O
a	O
single	O
Cat	B-Protocol
5e	I-Protocol
Ethernet	O
cable	O
,	O
is	O
capable	O
of	O
supplying	O
varying	O
levels	O
at	O
38.7	O
,	O
52.7	O
,	O
70	O
,	O
and	O
90W	O
.	O
</s>
<s>
In	O
a	O
passive	O
PoE	B-Device
system	O
,	O
the	O
injector	O
does	O
not	O
communicate	O
with	O
the	O
powered	B-Device
device	I-Device
to	O
negotiate	O
its	O
voltage	O
or	O
wattage	O
requirements	O
,	O
but	O
merely	O
supplies	O
power	O
at	O
all	O
times	O
.	O
</s>
<s>
Common	O
100Mbit/s	O
passive	O
applications	O
use	O
the	O
pinout	O
of	O
802.3af	B-Device
mode	O
B	O
(	O
see	O
)	O
with	O
DC	O
positive	O
on	O
pins	O
4	O
and	O
5	O
and	O
DC	O
negative	O
on	O
7	O
and	O
8	O
and	O
data	O
on	O
1	O
–	O
2	O
and	O
3	O
–	O
6	O
,	O
but	O
polarization	O
may	O
vary	O
.	O
</s>
<s>
Gigabit	O
passive	O
injectors	O
use	O
a	O
transformer	O
on	O
the	O
data	O
pins	O
to	O
allow	O
power	O
and	O
data	O
to	O
share	O
the	O
cable	O
and	O
are	O
typically	O
compatible	O
with	O
802.3af	B-Device
Mode	O
A	O
.	O
</s>
<s>
Devices	O
needing	O
5volts	O
cannot	O
typically	O
use	O
PoE	B-Device
at	O
5V	O
on	O
Ethernet	O
cable	O
beyond	O
short	O
distances	O
(	O
about	O
)	O
as	O
the	O
voltage	O
drop	O
of	O
the	O
cable	O
becomes	O
too	O
significant	O
,	O
so	O
a	O
24V	O
or	O
48V	B-Algorithm
to	O
5V	O
DC-DC	O
converter	O
is	O
required	O
at	O
the	O
remote	O
end	O
.	O
</s>
<s>
Passive	O
PoE	B-Device
power	O
sources	O
are	O
commonly	O
used	O
with	O
a	O
variety	O
of	O
indoor	O
and	O
outdoor	O
wireless	O
radio	O
equipment	O
,	O
most	O
commonly	O
from	O
Motorola	O
(	O
now	O
Cambium	O
)	O
,	O
Ubiquiti	O
Networks	O
,	O
MikroTik	O
and	O
others	O
.	O
</s>
<s>
Earlier	O
versions	O
of	O
passive	O
PoE	B-Device
24	O
VDC	O
power	O
sources	O
shipped	O
with	O
802.11a	O
,	O
802.11g	O
and	O
802.11n	O
based	O
radios	O
are	O
commonly	O
100Mbit/s	O
only	O
.	O
</s>
<s>
Passive	O
DC-to-DC	O
injectors	O
also	O
exist	O
which	O
convert	O
a	O
9V	O
to	O
36V	O
DC	O
,	O
or	O
36	O
V	O
to	O
72	O
V	O
DC	O
power	O
source	O
to	O
a	O
stabilized	O
24V	O
1A	O
,	O
48V	B-Algorithm
0.5A	O
,	O
or	O
up	O
to	O
48	O
V	O
2.0	O
A	O
PoE	B-Device
feed	O
with	O
'	O
+	O
 '	O
on	O
pins	O
4	O
&	O
5	O
and	O
''	O
on	O
pins	O
7	O
&	O
8	O
.	O
</s>
<s>
These	O
DC-to-DC	O
PoE	B-Device
injectors	I-Device
are	O
used	O
in	O
various	O
telecom	O
applications	O
.	O
</s>
<s>
The	O
ISO/IEC	O
TR	O
29125	O
and	O
Cenelec	O
EN	O
50174-99-1	O
draft	O
standards	O
outline	O
the	O
cable	O
bundle	O
temperature	O
rise	O
that	O
can	O
be	O
expected	O
from	O
the	O
use	O
of	O
4PPoE	B-Device
.	O
</s>
<s>
In	O
a	O
standard	O
unshielded	O
cable	O
,	O
the	O
PoE-related	O
temperature	O
rise	O
increases	O
by	O
a	O
factor	O
of	O
5	O
.	O
</s>
