In the
802.11n
s
y
s
t
e
m
,
two
new
f
or
m
a
t
s
,
called High
T
hr
o
ug
hpu
t
(HT), are defined
for the
Physical Layer, Mixed Mode, and Green Field.
If
a
s
y
s
t
e
m
runs 40 HT,
two
a
dj
a
c
e
n
t
20
M
H
z
channels are used. The larger 40 MHz bandwidth can provide
better
transmit quality and
s
pe
e
d.
K
e
y
s
Like passwords, keys open
(
de
c
r
y
p
t
)
and close (encrypt) messages. While many
encryption
a
l
g
or
i
t
hm
s
are commonly known and public,
the
key
m
us
t
be
ke
p
t
s
e
c
r
e
t
.
Local-Area
Network
(
L
AN
)
A small
da
t
a
network
covering a
limited
area, such as a building
or
group
of
buildings.
Most
L
A
Ns
c
onne
c
t
wor
k
s
t
a
t
i
o
ns
or
personal
c
omp
ut
e
r
s
.
LANs
let
many users share devices such as
pr
i
n
t
e
r
s
as
well
as
da
t
a
.
LANs also
facilitate
c
om
m
u
ni
c
a
t
i
on
through e-mail
or
c
ha
t
s
e
ss
i
o
ns
.
Media
Access Co
n
t
r
o
l
(MAC)
A
dd
r
e
ss
Address
a
ss
oc
i
a
t
e
d
with
every hardware device
on the
network.
Every 802.11 wireless device
ha
s
i
t
s
own specific MAC address. This
unique identifier
is hard-coded
into the
device and can
be
used
to
provide
s
e
c
ur
i
t
y
for
WLANs. When a
network
uses a MAC
t
a
bl
e,
only
the
802.11
radios
that
have
their
MAC addresses added
to that
ne
t
wor
k
'
s
MAC
t
a
bl
e
can access
the network.
Network
Address
T
r
a
n
s
l
a
t
i
on
(
NA
T
)
An Internet
s
t
a
nda
r
d
that
l
e
t
s
a LAN use one
s
e
t
of
IP addresses
for
internal
traffic
and a
s
e
c
ond
s
e
t
of
addresses
for
e
x
t
e
r
na
l
traffic.
Network
Time
Pr
o
t
o
c
o
l
(
N
T
P)
A protocol
that
l
e
t
s
devices synchronize
their time with
a
time
server. NTP uses
TCP
or
UDP
po
r
t
123 by
default.
P
a
ss
ph
r
a
s
e
A
text
s
t
r
i
ng
that
a
u
t
om
a
t
i
c
a
ll
y
g
e
ne
r
a
t
e
s
WEP keys
on
wireless
client
a
da
pt
e
r
s
.
Power Over
E
t
h
e
r
n
e
t
(
P
o
E
)
A PoE
provides power
to
PoE-enabled devices using an 8-pin
CAT
5
E
t
he
r
ne
t
cable, e
li
m
i
na
t
i
ng
the
need
for
a power source.
Preamble
S
ync
hr
oni
z
e
s
t
r
a
ns
m
i
ss
i
o
ns
in
a WLAN. The preamble
type
defines
the
l
e
n
g
t
h
of the
Cy
c
li
c
Redundancy Check block
for
c
om
m
u
ni
c
a
t
i
on
be
t
w
ee
n
a device and roaming wireless
s
t
a
t
i
ons.
Pr
o
t
e
c
t
e
d
E
x
t
e
n
s
i
b
l
e
Au
t
h
e
n
t
i
c
a
t
i
on
P
r
o
t
o
c
o
l
(
P
E
AP)
Authentication protocol
of
IEEE
802.1x used
to
send
authentication
da
t
a
and passwords
over
802.11
W
L
A
Ns
.
Qu
a
li
t
y
of
S
e
r
v
i
c
e
(
Qo
S
)
A
ne
t
wor
k
’
s
ability
to
deliver
da
t
a
with
minimum delay.
QoS
also refers
to the networking
m
e
t
ho
ds
used
to
provide bandwidth
for
real-time multimedia
applications.
R
e
mo
t
e
Au
t
h
e
n
t
i
c
a
t
i
on
Dial-In User
S
e
r
v
i
c
e
(
R
A
DI
US
)
Ne
t
wor
k
i
ng
protocol
that
provides
c
e
n
t
r
a
li
z
e
d
authentication,
a
u
t
h
or
i
z
a
t
i
o
n,
and
accounting
m
a
na
g
e
m
e
n
t
for
c
omp
ut
e
r
s
to
c
o
nne
c
t
and use a
network
service. Because
of
i
t
s
broad
s
uppo
r
t
and ubiquitous
na
t
u
r
e,
the
RADIUS
protocol
is
often
used by ISPs and
e
n
t
e
r
pr
i
s
e
s
to manage
access
to the
Internet
or
internal
ne
t
wor
k
s
,
WLANs, and
i
n
t
e
g
r
a
t
e
d
e-mail
s
e
r
v
i
c
e
s
.
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