<s>
A	O
wireless	B-Architecture
LAN	I-Architecture
(	O
WLAN	B-Architecture
)	O
is	O
a	O
wireless	B-General_Concept
computer	I-General_Concept
network	I-General_Concept
that	O
links	O
two	O
or	O
more	O
devices	O
using	O
wireless	O
communication	O
to	O
form	O
a	O
local	B-General_Concept
area	I-General_Concept
network	I-General_Concept
(	O
LAN	B-General_Concept
)	O
within	O
a	O
limited	O
area	O
such	O
as	O
a	O
home	O
,	O
school	O
,	O
computer	O
laboratory	O
,	O
campus	O
,	O
or	O
office	O
building	O
.	O
</s>
<s>
This	O
gives	O
users	O
the	O
ability	O
to	O
move	O
around	O
within	O
the	O
area	O
and	O
remain	O
connected	O
to	O
the	O
network	B-Architecture
.	O
</s>
<s>
Through	O
a	O
gateway	B-Application
,	O
a	O
WLAN	B-Architecture
can	O
also	O
provide	O
a	O
connection	O
to	O
the	O
wider	O
Internet	O
.	O
</s>
<s>
Wireless	B-Architecture
LANs	I-Architecture
based	O
on	O
the	O
IEEE	O
802.11	O
standards	O
are	O
the	O
most	O
widely	O
used	O
computer	B-Architecture
networks	I-Architecture
in	O
the	O
world	O
.	O
</s>
<s>
They	O
are	O
used	O
for	O
home	O
and	O
small	O
office	O
networks	O
that	O
link	O
together	O
laptop	B-Device
computers	I-Device
,	O
printers	O
,	O
smartphones	B-Application
,	O
Web	O
TVs	O
and	O
gaming	O
devices	O
with	O
a	O
wireless	B-Device
router	I-Device
,	O
which	O
links	O
them	O
to	O
the	O
internet	O
.	O
</s>
<s>
Hotspots	B-Application
provided	O
by	O
routers	O
at	O
restaurants	O
,	O
coffee	O
shops	O
,	O
hotels	O
,	O
libraries	O
,	O
and	O
airports	O
allow	O
consumers	O
to	O
access	O
the	O
internet	O
with	O
portable	O
wireless	O
devices	O
.	O
</s>
<s>
Norman	O
Abramson	O
,	O
a	O
professor	O
at	O
the	O
University	O
of	O
Hawaii	O
,	O
developed	O
the	O
world	O
's	O
first	O
wireless	B-General_Concept
computer	I-General_Concept
communication	O
network	B-Architecture
,	O
ALOHAnet	O
.	O
</s>
<s>
Wireless	B-Architecture
LAN	I-Architecture
hardware	O
initially	O
cost	O
so	O
much	O
that	O
it	O
was	O
only	O
used	O
as	O
an	O
alternative	O
to	O
cabled	O
LAN	B-General_Concept
in	O
places	O
where	O
cabling	O
was	O
difficult	O
or	O
impossible	O
.	O
</s>
<s>
This	O
allows	O
data	O
communications	O
to	O
avoid	O
the	O
crowded	O
2.4	O
GHz	O
band	O
,	O
which	O
is	O
also	O
shared	O
with	O
Bluetooth	B-Protocol
devices	O
and	O
microwave	O
ovens	O
.	O
</s>
<s>
Not	O
all	O
WLAN	B-Architecture
channels	O
are	O
available	O
in	O
all	O
regions	O
.	O
</s>
<s>
All	O
components	O
that	O
can	O
connect	O
into	O
a	O
wireless	O
medium	O
in	O
a	O
network	B-Architecture
are	O
referred	O
to	O
as	O
stations	O
.	O
</s>
<s>
All	O
stations	O
are	O
equipped	O
with	O
wireless	B-General_Concept
network	I-General_Concept
interface	I-General_Concept
controllers	I-General_Concept
.	O
</s>
<s>
Wireless	O
stations	O
fall	O
into	O
two	O
categories	O
:	O
wireless	B-Device
access	I-Device
points	I-Device
(	O
WAPs	O
)	O
and	O
clients	O
.	O
</s>
<s>
WAPs	O
are	O
base	O
stations	O
for	O
the	O
wireless	B-General_Concept
network	I-General_Concept
.	O
</s>
<s>
Wireless	O
clients	O
can	O
be	O
mobile	O
devices	O
such	O
as	O
laptops	B-Device
,	O
personal	B-Application
digital	I-Application
assistants	I-Application
,	O
VoIP	B-Device
phones	I-Device
and	O
other	O
smartphones	B-Application
,	O
or	O
non-portable	O
devices	O
such	O
as	O
desktop	O
computers	O
,	O
printers	O
,	O
and	O
workstations	B-Device
that	O
are	O
equipped	O
with	O
a	O
wireless	B-General_Concept
network	I-General_Concept
interface	I-General_Concept
.	O
</s>
<s>
An	O
independent	O
BSS	O
(	O
IBSS	O
)	O
is	O
an	O
ad	B-General_Concept
hoc	I-General_Concept
network	I-General_Concept
that	O
contains	O
no	O
access	O
points	O
,	O
which	O
means	O
they	O
cannot	O
connect	O
to	O
any	O
other	O
basic	O
service	O
set	O
.	O
</s>
<s>
The	O
concept	O
of	O
a	O
DS	O
can	O
be	O
used	O
to	O
increase	O
network	B-Architecture
coverage	O
through	O
roaming	O
between	O
cells	O
.	O
</s>
<s>
Current	O
wireless	B-General_Concept
distribution	I-General_Concept
systems	I-General_Concept
are	O
mostly	O
based	O
on	O
WDS	B-General_Concept
or	O
Mesh	O
protocols	O
,	O
though	O
other	O
systems	O
are	O
in	O
use	O
.	O
</s>
<s>
The	O
IEEE	O
802.11	O
has	O
two	O
basic	O
modes	O
of	O
operation	O
:	O
infrastructure	O
and	O
ad	B-General_Concept
hoc	I-General_Concept
mode	I-General_Concept
.	O
</s>
<s>
In	O
ad	B-General_Concept
hoc	I-General_Concept
mode	I-General_Concept
,	O
mobile	O
units	O
communicate	O
directly	O
peer-to-peer	O
.	O
</s>
<s>
In	O
infrastructure	O
mode	O
,	O
mobile	O
units	O
communicate	O
through	O
a	O
wireless	B-Device
access	I-Device
point	I-Device
(	O
WAP	O
)	O
that	O
also	O
serves	O
as	O
a	O
bridge	O
to	O
other	O
networks	O
such	O
as	O
a	O
local	B-General_Concept
area	I-General_Concept
network	I-General_Concept
or	O
the	O
Internet	O
.	O
</s>
<s>
Since	O
wireless	O
communication	O
uses	O
a	O
more	O
open	O
medium	O
for	O
communication	O
in	O
comparison	O
to	O
wired	O
LANs	B-General_Concept
,	O
the	O
802.11	O
designers	O
also	O
included	O
encryption	O
mechanisms	O
:	O
Wired	B-Protocol
Equivalent	I-Protocol
Privacy	I-Protocol
(	O
WEP	O
)	O
,	O
no	O
longer	O
considered	O
secure	O
,	O
Wi-Fi	O
Protected	O
Access	O
(	O
WPA	O
,	O
WPA2	O
,	O
WPA3	O
)	O
,	O
to	O
secure	O
wireless	B-General_Concept
computer	I-General_Concept
networks	I-General_Concept
.	O
</s>
<s>
Many	O
access	O
points	O
will	O
also	O
offer	O
Wi-Fi	B-Protocol
Protected	I-Protocol
Setup	I-Protocol
,	O
a	O
quick	O
,	O
but	O
no	O
longer	O
considered	O
secure	O
,	O
method	O
of	O
joining	O
a	O
new	O
device	O
to	O
an	O
encrypted	O
network	B-Architecture
.	O
</s>
<s>
In	O
infrastructure	O
mode	O
,	O
wireless	O
clients	O
,	O
such	O
as	O
laptops	B-Device
and	O
smartphones	B-Application
,	O
connect	O
to	O
the	O
WAP	O
to	O
join	O
the	O
network	B-Architecture
.	O
</s>
<s>
The	O
WAP	O
usually	O
has	O
a	O
wired	O
network	B-Architecture
connection	O
and	O
may	O
have	O
permanent	O
wireless	B-General_Concept
connections	I-General_Concept
to	O
other	O
WAPs	O
.	O
</s>
<s>
In	O
that	O
case	O
,	O
connecting	O
to	O
any	O
WAP	O
on	O
that	O
network	B-Architecture
joins	O
the	O
client	O
to	O
the	O
network	B-Architecture
,	O
and	O
the	O
client	O
software	O
will	O
try	O
to	O
choose	O
the	O
WAP	O
that	O
gives	O
the	O
best	O
service	O
,	O
such	O
as	O
the	O
WAP	O
with	O
the	O
strongest	O
signal	O
.	O
</s>
<s>
An	O
ad	B-General_Concept
hoc	I-General_Concept
network	I-General_Concept
is	O
a	O
network	B-Architecture
where	O
stations	O
communicate	O
only	O
peer-to-peer	O
(	O
P2P	O
)	O
.	O
</s>
<s>
A	O
Wi-Fi	O
Direct	O
network	B-Architecture
is	O
a	O
different	O
type	O
of	O
wireless	B-General_Concept
network	I-General_Concept
where	O
stations	O
communicate	O
peer-to-peer	O
.	O
</s>
<s>
In	O
a	O
peer-to-peer	O
network	B-Architecture
wireless	O
devices	O
within	O
range	O
of	O
each	O
other	O
can	O
discover	O
and	O
communicate	O
directly	O
without	O
involving	O
central	O
access	O
points	O
.	O
</s>
<s>
Group	O
owner	O
intent	O
value	O
can	O
depend	O
on	O
whether	O
the	O
wireless	O
device	O
performs	O
a	O
cross-connection	O
between	O
an	O
infrastructure	O
WLAN	B-Architecture
service	O
and	O
a	O
P2P	O
group	O
,	O
available	O
power	O
in	O
the	O
wireless	O
device	O
,	O
whether	O
the	O
wireless	O
device	O
is	O
already	O
a	O
group	O
owner	O
in	O
another	O
group	O
or	O
a	O
received	O
signal	O
strength	O
of	O
the	O
first	O
wireless	O
device	O
.	O
</s>
<s>
IEEE	O
802.11	O
defines	O
the	O
PHY	O
and	O
medium	B-Protocol
access	I-Protocol
control	I-Protocol
(	O
MAC	O
)	O
layers	O
based	O
on	O
carrier-sense	O
multiple	O
access	O
with	O
collision	O
avoidance	O
(	O
CSMA/CA	O
)	O
.	O
</s>
<s>
The	O
802.11	O
specification	O
includes	O
provisions	O
designed	O
to	O
minimize	O
collisions	O
because	O
mobile	O
units	O
have	O
to	O
contend	O
with	O
the	O
hidden	B-General_Concept
node	I-General_Concept
problem	I-General_Concept
where	O
two	O
mobile	O
units	O
may	O
both	O
be	O
in	O
range	O
of	O
a	O
common	O
access	O
point	O
,	O
but	O
out	O
of	O
range	O
of	O
each	O
other	O
.	O
</s>
<s>
A	O
wireless	O
Ethernet	O
bridge	O
allows	O
the	O
connection	O
of	O
devices	O
on	O
a	O
wired	O
Ethernet	O
network	B-Architecture
to	O
a	O
wireless	B-General_Concept
network	I-General_Concept
.	O
</s>
<s>
The	O
bridge	O
acts	O
as	O
the	O
connection	O
point	O
to	O
the	O
wireless	B-Architecture
LAN	I-Architecture
.	O
</s>
<s>
A	O
wireless	B-General_Concept
distribution	I-General_Concept
system	I-General_Concept
(	O
WDS	B-General_Concept
)	O
enables	O
the	O
wireless	O
interconnection	O
of	O
access	O
points	O
in	O
an	O
IEEE	O
802.11	O
network	B-Architecture
.	O
</s>
<s>
It	O
allows	O
a	O
wireless	B-General_Concept
network	I-General_Concept
to	O
be	O
expanded	O
using	O
multiple	O
access	O
points	O
without	O
the	O
need	O
for	O
a	O
wired	O
backbone	O
to	O
link	O
them	O
,	O
as	O
is	O
traditionally	O
required	O
.	O
</s>
<s>
The	O
notable	O
advantage	O
of	O
a	O
WDS	B-General_Concept
over	O
some	O
other	O
solutions	O
is	O
that	O
it	O
preserves	O
the	O
MAC	O
addresses	O
of	O
client	O
packets	O
across	O
links	O
between	O
access	O
points	O
.	O
</s>
<s>
WDS	B-General_Concept
capability	O
may	O
also	O
be	O
referred	O
to	O
as	O
repeater	O
mode	O
because	O
it	O
appears	O
to	O
bridge	O
and	O
accept	O
wireless	O
clients	O
at	O
the	O
same	O
time	O
(	O
unlike	O
traditional	O
bridging	O
)	O
.	O
</s>
<s>
All	O
base	O
stations	O
in	O
a	O
WDS	B-General_Concept
must	O
be	O
configured	O
to	O
use	O
the	O
same	O
radio	O
channel	O
,	O
and	O
share	O
WEP	B-Protocol
keys	I-Protocol
or	O
WPA	O
keys	O
if	O
they	O
are	O
used	O
.	O
</s>
<s>
WDS	B-General_Concept
also	O
requires	O
that	O
every	O
base	O
station	O
be	O
configured	O
to	O
forward	O
to	O
others	O
in	O
the	O
system	O
as	O
mentioned	O
above	O
.	O
</s>
<s>
There	O
are	O
two	O
definitions	O
for	O
wireless	B-Architecture
LAN	I-Architecture
roaming	O
:	O
</s>
<s>
Internal	O
roaming	O
:	O
The	O
mobile	O
station	O
(	O
MS	O
)	O
moves	O
from	O
one	O
access	O
point	O
(	O
AP	O
)	O
to	O
another	O
AP	O
within	O
a	O
home	O
network	B-Architecture
if	O
the	O
signal	O
strength	O
is	O
too	O
weak	O
.	O
</s>
<s>
The	O
billing	O
of	O
QoS	O
is	O
in	O
the	O
home	O
network	B-Architecture
.	O
</s>
<s>
A	O
MS	O
roaming	O
from	O
one	O
access	O
point	O
to	O
another	O
often	O
interrupts	O
the	O
flow	O
of	O
data	O
between	O
the	O
MS	O
and	O
an	O
application	O
connected	O
to	O
the	O
network	B-Architecture
.	O
</s>
<s>
External	O
roaming	O
:	O
The	O
MS	O
(	O
client	O
)	O
moves	O
into	O
a	O
WLAN	B-Architecture
of	O
another	O
wireless	B-General_Concept
Internet	I-General_Concept
service	I-General_Concept
provider	I-General_Concept
(	O
WISP	O
)	O
and	O
takes	O
their	O
services	O
.	O
</s>
<s>
The	O
user	O
can	O
use	O
a	O
foreign	O
network	B-Architecture
independently	O
from	O
their	O
home	O
network	B-Architecture
,	O
provided	O
that	O
the	O
foreign	O
network	B-Architecture
allows	O
visiting	O
users	O
on	O
their	O
network	B-Architecture
.	O
</s>
<s>
There	O
must	O
be	O
special	O
authentication	O
and	O
billing	O
systems	O
for	O
mobile	O
services	O
in	O
a	O
foreign	O
network	B-Architecture
.	O
</s>
