<s>
Dynamic	B-Protocol
Frequency	I-Protocol
Selection	I-Protocol
(	O
DFS	O
)	O
is	O
a	O
channel	B-Protocol
allocation	I-Protocol
scheme	I-Protocol
specified	O
for	O
wireless	B-Architecture
LAN	I-Architecture
,	O
commonly	O
known	O
as	O
Wi-Fi	O
.	O
</s>
<s>
It	O
is	O
designed	O
to	O
prevent	O
electromagnetic	O
interference	O
by	O
avoiding	O
co-channel	O
operation	O
with	O
systems	O
that	O
predated	O
Wi-Fi	O
,	O
such	O
as	O
military	B-Application
radar	I-Application
,	O
satellite	O
communication	O
,	O
and	O
weather	B-Application
radar	I-Application
,	O
and	O
also	O
to	O
provide	O
on	O
aggregate	O
a	O
near-uniform	O
loading	O
of	O
the	O
spectrum	O
(	O
Uniform	O
Spreading	O
)	O
.	O
</s>
<s>
It	O
was	O
standardized	O
in	O
2003	O
as	O
part	O
of	O
IEEE	B-Protocol
802.11h	I-Protocol
.	O
</s>
<s>
During	O
this	O
phase	O
,	O
the	O
access	O
point	O
is	O
in	O
a	O
passive	O
state	O
scanning	O
for	O
radar	B-Application
signals	O
.	O
</s>
<s>
Thereafter	O
,	O
the	O
access	O
point	O
performs	O
In-Service	O
Monitoring	O
(	O
ISM	O
)	O
to	O
detect	O
active	O
radar	B-Application
signals	O
;	O
if	O
radar	B-Application
is	O
detected	O
,	O
and	O
the	O
access	O
point	O
is	O
configured	O
to	O
automatically	O
select	O
a	O
channel	O
,	O
it	O
broadcasts	O
a	O
switch	O
channel	O
event	O
to	O
its	O
clients	O
and	O
follows	O
by	O
switching	O
the	O
channel	O
.	O
</s>
<s>
The	O
actual	O
mechanism	O
,	O
durations	O
,	O
radar	B-Application
pulse	O
pattern	O
,	O
power	O
levels	O
,	O
and	O
frequency	O
bands	O
on	O
which	O
DFS	O
is	O
enforced	O
vary	O
by	O
country	O
and	O
jurisdiction	O
.	O
</s>
<s>
DFS	O
is	O
mandated	O
for	O
the	O
5470	O
–	O
5725MHz	O
U-NII	B-Algorithm
band	I-Algorithm
in	O
United	O
States	O
by	O
the	O
FCC	O
.	O
</s>
<s>
Prior	O
to	O
the	O
introduction	O
of	O
Wi-Fi	O
,	O
one	O
of	O
the	O
biggest	O
applications	O
of	O
the	O
5GHz	O
band	O
was	O
Terminal	B-Algorithm
Doppler	I-Algorithm
Weather	I-Algorithm
Radar	I-Algorithm
.	O
</s>
<s>
Implementation	O
and	O
configuration	O
problems	O
caused	O
significant	O
disruption	O
in	O
weather	B-Application
radar	I-Application
operations	O
in	O
countries	O
around	O
the	O
world	O
.	O
</s>
<s>
In	O
Hungary	O
,	O
the	O
weather	B-Application
radar	I-Application
system	O
was	O
declared	O
non-operational	O
for	O
more	O
than	O
a	O
month	O
.	O
</s>
<s>
Due	O
to	O
the	O
severity	O
of	O
interference	O
,	O
South	O
African	O
weather	O
services	O
ended	O
up	O
abandoning	O
C	O
band	O
operation	O
,	O
switching	O
their	O
radar	B-Application
network	O
to	O
S	B-Algorithm
band	I-Algorithm
.	O
</s>
<s>
There	O
are	O
several	O
ways	O
in	O
which	O
this	O
can	O
be	O
achieved	O
,	O
either	O
on	O
device	O
,	O
or	O
by	O
some	O
other	O
form	O
of	O
network	O
management	O
hosted	O
locally	O
on	O
device	O
,	O
or	O
in	O
a	O
WLAN	B-Architecture
controller	O
that	O
has	O
the	O
ability	O
to	O
control	O
channel	O
selection	O
of	O
Wi-Fi	O
Access	O
Points	O
.	O
</s>
