<s>
In	O
IEEE	O
802.11	O
wireless	O
local	O
area	O
networking	O
standards	O
(	O
including	O
Wi-Fi	O
)	O
,	O
a	O
service	B-General_Concept
set	I-General_Concept
is	O
a	O
group	O
of	O
wireless	O
network	O
devices	O
which	O
share	O
a	O
service	B-General_Concept
set	I-General_Concept
identifier	I-General_Concept
(	O
SSID	O
)	O
—	O
typically	O
the	O
natural	O
language	O
label	O
that	O
users	O
see	O
as	O
a	O
network	O
name	O
.	O
</s>
<s>
(	O
For	O
example	O
,	O
all	O
of	O
the	O
devices	O
that	O
together	O
form	O
and	O
use	O
a	O
Wi‑Fi	O
network	O
called	O
Foo	O
are	O
a	O
service	B-General_Concept
set	I-General_Concept
.	O
)	O
</s>
<s>
A	O
service	B-General_Concept
set	I-General_Concept
forms	O
a	O
logical	O
network	O
of	O
nodes	B-Protocol
operating	O
with	O
shared	O
link-layer	O
networking	O
parameters	O
;	O
they	O
form	O
one	O
logical	O
network	O
segment	O
.	O
</s>
<s>
A	O
service	B-General_Concept
set	I-General_Concept
is	O
either	O
a	O
basic	B-General_Concept
service	I-General_Concept
set	I-General_Concept
(	O
BSS	O
)	O
or	O
an	O
extended	O
service	B-General_Concept
set	I-General_Concept
(	O
ESS	O
)	O
.	O
</s>
<s>
A	O
basic	B-General_Concept
service	I-General_Concept
set	I-General_Concept
is	O
a	O
subgroup	O
,	O
within	O
a	O
service	B-General_Concept
set	I-General_Concept
,	O
of	O
devices	O
that	O
share	O
physical-layer	O
medium	O
access	O
characteristics	O
(	O
e.g.	O
</s>
<s>
The	O
basic	B-General_Concept
service	I-General_Concept
set	I-General_Concept
is	O
defined	O
by	O
a	O
basic	B-General_Concept
service	I-General_Concept
set	I-General_Concept
identifier	O
(	O
BSSID	B-General_Concept
)	O
shared	O
by	O
all	O
devices	O
within	O
it	O
.	O
</s>
<s>
The	O
BSSID	B-General_Concept
is	O
a	O
48-bit	O
label	O
that	O
conform	O
to	O
MAC-48	O
conventions	O
.	O
</s>
<s>
While	O
a	O
device	O
may	O
have	O
multiple	O
BSSIDs	B-General_Concept
,	O
usually	O
each	O
BSSID	B-General_Concept
is	O
associated	O
with	O
at	O
most	O
one	O
basic	B-General_Concept
service	I-General_Concept
set	I-General_Concept
at	O
a	O
time	O
.	O
</s>
<s>
A	O
basic	B-General_Concept
service	I-General_Concept
set	I-General_Concept
should	O
not	O
be	O
confused	O
with	O
the	O
coverage	O
area	O
of	O
an	O
access	O
point	O
,	O
known	O
as	O
the	O
basic	O
service	O
area	O
(	O
BSA	O
)	O
.	O
</s>
<s>
Each	O
basic	B-General_Concept
service	I-General_Concept
set	I-General_Concept
has	O
a	O
unique	O
identifier	O
,	O
a	O
BSSID	B-General_Concept
,	O
which	O
is	O
a	O
48-bit	O
number	O
that	O
follows	O
MAC	O
address	O
conventions	O
.	O
</s>
<s>
An	O
infrastructure	O
BSSID	B-General_Concept
is	O
usually	O
non-configurable	O
,	O
in	O
which	O
case	O
it	O
is	O
either	O
preset	O
during	O
manufacture	O
or	O
mathematically	O
derived	O
from	O
a	O
preset	O
value	O
such	O
as	O
a	O
serial	O
number	O
or	O
a	O
MAC	O
address	O
of	O
another	O
network	O
interface	O
.	O
</s>
<s>
As	O
with	O
the	O
MAC	O
addresses	O
used	O
for	O
Ethernet	O
devices	O
,	O
an	O
infrastructure	O
BSSID	B-General_Concept
is	O
a	O
combination	O
of	O
a	O
24-bit	O
organizationally	O
unique	O
identifier	O
(	O
OUI	O
,	O
the	O
manufacturer	O
's	O
identity	O
)	O
and	O
a	O
24-bit	O
serial	O
number	O
.	O
</s>
<s>
A	O
BSSID	B-General_Concept
with	O
a	O
value	O
of	O
all	O
1s	O
is	O
used	O
to	O
indicate	O
the	O
wildcard	O
BSSID	B-General_Concept
,	O
usable	O
only	O
during	O
probe	O
requests	O
or	O
for	O
communications	O
that	O
take	O
place	O
outside	O
the	O
context	O
of	O
a	O
BSS	O
.	O
</s>
<s>
In	O
contrast	O
to	O
the	O
stations	O
in	O
an	O
infrastructure-mode	O
network	O
,	O
the	O
stations	O
in	O
a	O
wireless	B-General_Concept
ad	I-General_Concept
hoc	I-General_Concept
network	I-General_Concept
communicate	O
directly	O
with	O
one	O
another	O
,	O
i.e.	O
</s>
<s>
In	O
this	O
form	O
of	O
peer-to-peer	O
wireless	O
networking	O
,	O
the	O
peers	O
form	O
an	O
independent	O
basic	B-General_Concept
service	I-General_Concept
set	I-General_Concept
(	O
IBSS	O
)	O
.	O
</s>
<s>
A	O
mesh	O
basic	B-General_Concept
service	I-General_Concept
set	I-General_Concept
(	O
MBSS	O
)	O
forms	O
a	O
self-contained	O
network	O
of	O
mesh	O
stations	O
that	O
share	O
a	O
mesh	O
profile	O
.	O
</s>
<s>
Each	O
node	O
may	O
also	O
be	O
an	O
access	O
point	O
hosting	O
its	O
own	O
basic	B-General_Concept
service	I-General_Concept
set	I-General_Concept
,	O
for	O
example	O
using	O
the	O
mesh	O
BSS	O
to	O
provide	O
Internet	O
access	O
for	O
local	O
users	O
.	O
</s>
<s>
The	O
formation	O
of	O
the	O
mesh	O
's	O
BSS	O
,	O
as	O
well	O
as	O
wireless	O
traffic	O
management	O
(	O
including	O
path	O
selection	O
and	O
forwarding	O
)	O
is	O
negotiated	O
between	O
the	O
nodes	B-Protocol
of	O
the	O
mesh	O
infrastructure	O
.	O
</s>
<s>
The	O
service	B-General_Concept
set	I-General_Concept
identifier	I-General_Concept
(	O
SSID	O
)	O
defines	O
a	O
service	B-General_Concept
set	I-General_Concept
or	O
extends	O
service	B-General_Concept
set	I-General_Concept
.	O
</s>
<s>
Unlike	O
basic	B-General_Concept
service	I-General_Concept
set	I-General_Concept
identifiers	O
,	O
SSIDs	O
are	O
usually	O
customizable	O
.	O
</s>
<s>
These	O
SSIDs	O
can	O
be	O
zero	O
to	O
32	O
octets	O
(	O
32	O
bytes	B-Application
)	O
long	O
,	O
and	O
are	O
,	O
for	O
convenience	O
,	O
usually	O
in	O
a	O
natural	O
language	O
,	O
such	O
as	O
English	O
.	O
</s>
<s>
Once	O
a	O
device	O
has	O
associated	O
with	O
a	O
basic	B-General_Concept
service	I-General_Concept
set	I-General_Concept
,	O
for	O
efficiency	O
,	O
the	O
SSID	O
is	O
not	O
sent	O
within	O
packet	O
headers	O
;	O
only	O
BSSIDs	B-General_Concept
are	O
used	O
for	O
addressing	O
.	O
</s>
<s>
An	O
extended	O
service	B-General_Concept
set	I-General_Concept
(	O
ESS	O
)	O
is	O
a	O
wireless	O
network	O
,	O
created	O
by	O
multiple	O
access	O
points	O
,	O
which	O
appears	O
to	O
users	O
as	O
a	O
single	O
,	O
seamless	O
network	O
,	O
such	O
as	O
a	O
network	O
covering	O
a	O
home	O
or	O
office	O
that	O
is	O
too	O
large	O
for	O
reliable	O
coverage	O
by	O
a	O
single	O
access	O
point	O
.	O
</s>
<s>
It	O
is	O
a	O
set	O
of	O
one	O
or	O
more	O
infrastructure	O
basic	B-General_Concept
service	I-General_Concept
sets	I-General_Concept
on	O
a	O
common	O
logical	O
network	O
segment	O
(	O
i.e.	O
</s>
<s>
Key	O
to	O
the	O
concept	O
is	O
that	O
the	O
participating	O
basic	B-General_Concept
service	I-General_Concept
sets	I-General_Concept
appear	O
as	O
a	O
single	O
network	O
to	O
the	O
logical	O
link	O
control	O
layer	O
.	O
</s>
<s>
Thus	O
,	O
from	O
the	O
perspective	O
of	O
the	O
logical	O
link	O
control	O
layer	O
,	O
stations	O
within	O
an	O
ESS	O
may	O
communicate	O
with	O
one	O
another	O
,	O
and	O
mobile	O
stations	O
may	O
move	O
transparently	O
from	O
one	O
participating	O
basic	B-General_Concept
service	I-General_Concept
set	I-General_Concept
to	O
another	O
(	O
within	O
the	O
same	O
ESS	O
)	O
.	O
</s>
<s>
Extended	O
service	B-General_Concept
sets	I-General_Concept
make	O
possible	O
distribution	O
services	O
such	O
as	O
centralized	O
authentication	O
.	O
</s>
<s>
The	O
basic	B-General_Concept
service	I-General_Concept
sets	I-General_Concept
formed	O
in	O
wireless	B-General_Concept
ad	I-General_Concept
hoc	I-General_Concept
networks	I-General_Concept
are	O
,	O
by	O
definition	O
,	O
independent	O
from	O
other	O
BSSs	O
,	O
and	O
an	O
independent	O
BSS	O
cannot	O
therefore	O
be	O
part	O
of	O
an	O
extended	O
infrastructure	O
.	O
</s>
<s>
In	O
that	O
formal	O
sense	O
an	O
independent	O
BSS	O
has	O
no	O
extended	O
service	B-General_Concept
set	I-General_Concept
.	O
</s>
<s>
However	O
,	O
the	O
network	O
packets	O
of	O
both	O
independent	O
BSSs	O
and	O
infrastructure	O
BSSs	O
have	O
a	O
logical	O
network	O
service	B-General_Concept
set	I-General_Concept
identifier	I-General_Concept
,	O
and	O
the	O
logical	O
link	O
control	O
does	O
not	O
distinguish	O
between	O
the	O
use	O
of	O
that	O
field	O
to	O
name	O
an	O
ESS	O
network	O
,	O
and	O
the	O
use	O
of	O
that	O
field	O
to	O
name	O
a	O
peer-to-peer	O
ad	O
hoc	O
network	O
.	O
</s>
