<s>
A	O
modulator-demodulator	O
or	O
modem	B-Application
is	O
a	O
computer	B-Architecture
hardware	I-Architecture
device	O
that	O
converts	O
data	O
from	O
a	O
digital	B-General_Concept
format	I-General_Concept
into	O
a	O
format	O
suitable	O
for	O
an	O
analog	O
transmission	O
medium	O
such	O
as	O
telephone	O
or	O
radio	O
.	O
</s>
<s>
A	O
modem	B-Application
transmits	O
data	O
by	O
modulating	O
one	O
or	O
more	O
carrier	O
wave	O
signals	O
to	O
encode	O
digital	B-General_Concept
information	I-General_Concept
,	O
while	O
the	O
receiver	O
demodulates	B-Device
the	O
signal	O
to	O
recreate	O
the	O
original	O
digital	B-General_Concept
information	I-General_Concept
.	O
</s>
<s>
Modems	B-Application
can	O
be	O
used	O
with	O
almost	O
any	O
means	O
of	O
transmitting	O
analog	O
signals	O
,	O
from	O
light-emitting	O
diodes	O
to	O
radio	O
.	O
</s>
<s>
Early	O
modems	B-Application
were	O
devices	O
that	O
used	O
audible	O
sounds	O
suitable	O
for	O
transmission	O
over	O
traditional	O
telephone	O
systems	O
and	O
leased	B-Architecture
lines	I-Architecture
.	O
</s>
<s>
By	O
the	O
1970s	O
,	O
higher	O
speeds	O
of	O
1,200	O
and	O
2,400	O
bit/s	O
for	O
asynchronous	O
dial	O
connections	O
,	O
4,800	O
bit/s	O
for	O
synchronous	O
leased	B-Architecture
line	I-Architecture
connections	O
and	O
35kbit/s	O
for	O
synchronous	O
conditioned	O
leased	B-Architecture
lines	I-Architecture
were	O
available	O
.	O
</s>
<s>
By	O
the	O
1980s	O
,	O
less	O
expensive	O
1,200	O
and	O
2,400	O
bit/s	O
dialup	O
modems	B-Application
were	O
being	O
released	O
,	O
and	O
modems	B-Application
working	O
on	O
radio	O
and	O
other	O
systems	O
were	O
available	O
.	O
</s>
<s>
As	O
device	O
sophistication	O
grew	O
rapidly	O
in	O
the	O
late	O
1990s	O
,	O
telephone-based	O
modems	B-Application
quickly	O
exhausted	O
the	O
available	O
bandwidth	O
,	O
reaching	O
56kbit/s	O
.	O
</s>
<s>
The	O
rise	O
of	O
public	O
use	O
of	O
the	O
internet	O
during	O
the	O
late	O
1990s	O
led	O
to	O
demands	O
for	O
much	O
higher	O
performance	O
,	O
leading	O
to	O
the	O
move	O
away	O
from	O
audio-based	O
systems	O
to	O
entirely	O
new	O
encodings	O
on	O
cable	B-Device
television	I-Device
lines	I-Device
and	O
short-range	O
signals	O
in	O
subcarriers	O
on	O
telephone	O
lines	O
.	O
</s>
<s>
The	O
move	O
to	O
cellular	O
telephones	O
,	O
especially	O
in	O
the	O
late	O
1990s	O
and	O
the	O
emergence	O
of	O
smartphones	B-Application
in	O
the	O
2000s	O
led	O
to	O
the	O
development	O
of	O
ever-faster	O
radio-based	O
systems	O
.	O
</s>
<s>
Today	O
,	O
modems	B-Application
are	O
ubiquitous	O
and	O
largely	O
invisible	O
,	O
included	O
in	O
almost	O
every	O
mobile	O
computing	O
device	O
in	O
one	O
form	O
or	O
another	O
,	O
and	O
generally	O
capable	O
of	O
speeds	O
on	O
the	O
order	O
of	O
tens	O
or	O
hundreds	O
of	O
megabytes	O
per	O
second	O
.	O
</s>
<s>
Modems	B-Application
are	O
frequently	O
classified	O
by	O
the	O
maximum	O
amount	O
of	O
data	O
they	O
can	O
send	O
in	O
a	O
given	O
unit	O
of	O
time	O
,	O
usually	O
expressed	O
in	O
bits	O
per	O
second	O
(	O
symbol	O
bit/s	O
,	O
sometimes	O
abbreviated	O
"	O
bps	O
"	O
)	O
or	O
rarely	O
in	O
bytes	O
per	O
second	O
(	O
symbol	O
B/s	O
)	O
.	O
</s>
<s>
Modern	O
broadband	B-General_Concept
modem	I-General_Concept
speeds	O
are	O
typically	O
expressed	O
in	O
megabits	O
per	O
second	O
(	O
Mbit/s	O
)	O
.	O
</s>
<s>
Historically	O
,	O
modems	B-Application
were	O
often	O
classified	O
by	O
their	O
symbol	O
rate	O
,	O
measured	O
in	O
baud	O
.	O
</s>
<s>
The	O
baud	O
unit	O
denotes	O
symbols	O
per	O
second	O
,	O
or	O
the	O
number	O
of	O
times	O
per	O
second	O
the	O
modem	B-Application
sends	O
a	O
new	O
signal	O
.	O
</s>
<s>
By	O
contrast	O
,	O
the	O
original	O
ITU	O
V.22	O
standard	O
,	O
which	O
could	O
transmit	O
and	O
receive	O
four	O
distinct	O
symbols	O
(	O
twobits	O
per	O
symbol	O
)	O
,	O
transmitted	O
1,200	O
bits	O
by	O
sending	O
600	O
symbols	O
per	O
second	O
(	O
600baud	O
)	O
using	O
phase-shift	B-General_Concept
keying	I-General_Concept
.	O
</s>
<s>
Many	O
modems	B-Application
are	O
variable-rate	O
,	O
permitting	O
them	O
to	O
be	O
used	O
over	O
a	O
medium	O
with	O
less	O
than	O
ideal	O
characteristics	O
,	O
such	O
as	O
a	O
telephone	O
line	O
that	O
is	O
of	O
poor	O
quality	O
or	O
is	O
too	O
long	O
.	O
</s>
<s>
This	O
capability	O
is	O
often	O
adaptive	O
so	O
that	O
a	O
modem	B-Application
can	O
discover	O
the	O
maximum	O
practical	O
transmission	O
rate	O
during	O
the	O
connect	O
phase	O
,	O
or	O
during	O
operation	O
.	O
</s>
<s>
Modems	B-Application
grew	O
out	O
of	O
the	O
need	O
to	O
connect	O
teleprinters	O
over	O
ordinary	O
phone	O
lines	O
instead	O
of	O
the	O
more	O
expensive	O
leased	B-Architecture
lines	I-Architecture
which	O
had	O
previously	O
been	O
used	O
for	O
current	O
loop	O
–	O
based	O
teleprinters	O
and	O
automated	O
telegraphs	O
.	O
</s>
<s>
The	O
earliest	O
devices	O
that	O
satisfy	O
the	O
definition	O
of	O
a	O
modem	B-Application
may	O
be	O
the	O
multiplexers	O
used	O
by	O
news	O
wire	O
services	O
in	O
the	O
1920s	O
.	O
</s>
<s>
In	O
1941	O
,	O
the	O
Allies	O
developed	O
a	O
voice	O
encryption	O
system	O
called	O
SIGSALY	O
which	O
used	O
a	O
vocoder	B-Application
to	O
digitize	O
speech	O
,	O
then	O
encrypted	O
the	O
speech	O
with	O
one-time	O
pad	O
and	O
encoded	O
the	O
digital	B-General_Concept
data	I-General_Concept
as	O
tones	O
using	O
frequency	O
shift	O
keying	O
.	O
</s>
<s>
This	O
was	O
also	O
a	O
digital	O
modulation	B-Application
technique	O
,	O
making	O
this	O
an	O
early	O
modem	B-Application
.	O
</s>
<s>
Commercial	O
modems	B-Application
largely	O
did	O
not	O
become	O
available	O
until	O
the	O
late	O
1950s	O
,	O
when	O
the	O
rapid	O
development	O
of	O
computer	O
technology	O
created	O
demand	O
for	O
a	O
method	O
of	O
connecting	O
computers	O
together	O
over	O
long	O
distances	O
,	O
resulting	O
in	O
the	O
Bell	O
Company	O
and	O
then	O
other	O
businesses	O
producing	O
an	O
increasing	O
number	O
of	O
computer	B-Application
modems	I-Application
for	O
use	O
over	O
both	O
switched	O
and	O
leased	O
telephone	O
lines	O
.	O
</s>
<s>
Later	O
developments	O
would	O
produce	O
modems	B-Application
that	O
operated	O
over	O
cable	B-Device
television	I-Device
lines	I-Device
,	O
power	B-Device
lines	I-Device
,	O
and	O
various	O
radio	O
technologies	O
,	O
as	O
well	O
as	O
modems	B-Application
that	O
achieved	O
much	B-General_Concept
higher	I-General_Concept
speeds	I-General_Concept
over	O
telephone	O
lines	O
.	O
</s>
<s>
A	O
dial-up	B-Application
modem	I-Application
transmits	O
computer	O
data	O
over	O
an	O
ordinary	O
switched	O
telephone	O
line	O
that	O
has	O
not	O
been	O
designed	O
for	O
data	O
use	O
.	O
</s>
<s>
This	O
contrasts	O
with	O
leased	B-Architecture
line	I-Architecture
modems	B-Application
,	O
which	O
also	O
operate	O
over	O
lines	O
provided	O
by	O
a	O
telephone	O
company	O
,	O
but	O
ones	O
which	O
are	O
intended	O
for	O
data	O
use	O
and	O
do	O
not	O
impose	O
the	O
same	O
signaling	O
constraints	O
.	O
</s>
<s>
The	O
modulated	B-Application
data	O
must	O
fit	O
the	O
frequency	O
constraints	O
of	O
a	O
normal	O
voice	O
audio	O
signal	O
.	O
</s>
<s>
Early	O
modems	B-Application
,	O
including	O
acoustic	B-Device
coupled	I-Device
modems	B-Application
,	O
relied	O
on	O
the	O
communicating	O
parties	O
or	O
an	O
automatic	O
calling	O
unit	O
to	O
dial	O
and	O
establish	O
a	O
voice	O
connection	O
before	O
switching	O
their	O
modems	B-Application
to	O
line	O
;	O
more	O
modern	O
devices	O
are	O
able	O
to	O
perform	O
the	O
actions	O
needed	O
to	O
connect	O
a	O
call	O
through	O
a	O
telephone	O
exchange	O
,	O
e.g.	O
,	O
picking	O
up	O
the	O
line	O
,	O
dialing	O
,	O
understanding	O
signals	O
sent	O
back	O
by	O
phone	O
company	O
equipment	O
(	O
dialtone	O
,	O
ringing	O
,	O
busy	O
signal	O
)	O
recognizing	O
incoming	O
ring	O
signals	O
and	O
answering	O
calls	O
.	O
</s>
<s>
Dial-up	B-Application
modems	I-Application
have	O
been	O
made	O
in	O
a	O
wide	O
variety	O
of	O
speeds	O
and	O
capabilities	O
,	O
with	O
many	O
capable	O
of	O
testing	O
the	O
line	O
they	O
are	O
calling	O
over	O
and	O
selecting	O
the	O
most	O
advanced	O
signaling	O
mode	O
that	O
the	O
line	O
can	O
support	O
.	O
</s>
<s>
Generally	O
speaking	O
,	O
the	O
fastest	O
dialup	O
modems	B-Application
ever	O
available	O
to	O
consumers	O
never	O
exceeded	O
56	O
kbit/s	O
and	O
never	O
achieved	O
that	O
speed	O
in	O
both	O
directions	O
.	O
</s>
<s>
The	O
dial-up	B-Application
modem	I-Application
was	O
once	O
a	O
widely	O
known	O
technology	O
,	O
since	O
it	O
was	O
mass-marketed	O
to	O
consumers	O
in	O
many	O
countries	O
for	O
dial-up	O
internet	O
access	O
.	O
</s>
<s>
In	O
the	O
1990s	O
,	O
tens	O
of	O
millions	O
of	O
people	O
in	O
the	O
United	O
States	O
used	O
dial-up	B-Application
modems	I-Application
for	O
internet	O
access	O
.	O
</s>
<s>
Dial-up	O
service	O
has	O
since	O
been	O
largely	O
supplanted	O
by	O
broadband	B-General_Concept
internet	O
,	O
such	O
as	O
DSL	O
,	O
which	O
typically	O
still	O
uses	O
a	O
modem	B-Application
,	O
but	O
of	O
a	O
very	O
different	O
type	O
which	O
may	O
still	O
operate	O
over	O
a	O
normal	O
phone	O
line	O
,	O
but	O
with	O
substantially	O
relaxed	O
constraints	O
.	O
</s>
<s>
Mass	O
production	O
of	O
telephone	O
line	O
modems	B-Application
in	O
the	O
United	O
States	O
began	O
as	O
part	O
of	O
the	O
SAGE	B-Device
air-defense	O
system	O
in	O
1958	O
,	O
connecting	O
terminals	O
at	O
various	O
airbases	O
,	O
radar	O
sites	O
,	O
and	O
command-and-control	O
centers	O
to	O
the	O
SAGE	B-Device
director	O
centers	O
scattered	O
around	O
the	O
United	O
States	O
and	O
Canada	O
.	O
</s>
<s>
Shortly	O
afterwards	O
in	O
1959	O
,	O
the	O
technology	O
in	O
the	O
SAGE	B-Device
modems	B-Application
was	O
made	O
available	O
commercially	O
as	O
the	O
Bell	O
101	O
,	O
which	O
provided	O
110	O
bit/s	O
speeds	O
.	O
</s>
<s>
Bell	O
called	O
this	O
and	O
several	O
other	O
early	O
modems	B-Application
"	O
datasets	O
"	O
.	O
</s>
<s>
Some	O
early	O
modems	B-Application
were	O
based	O
on	O
touch-tone	O
frequencies	O
,	O
such	O
as	O
Bell	O
400-style	O
touch-tone	O
modems	B-Application
.	O
</s>
<s>
Frequency-shift	O
keying	O
was	O
used	O
,	O
with	O
the	O
call	O
originator	O
transmitting	O
at	O
1,070	O
or	O
1,270	O
Hz	O
and	O
the	O
answering	O
modem	B-Application
transmitting	O
at	O
2,025	O
or	O
2,225	O
Hz	O
.	O
</s>
<s>
The	O
103	O
modem	B-Application
would	O
eventually	O
become	O
a	O
de	O
facto	O
standard	O
once	O
third-party	O
(	O
non-AT	O
&T	O
modems	B-Application
)	O
reached	O
the	O
market	O
,	O
and	O
throughout	O
the	O
1970s	O
,	O
independently	O
made	O
modems	B-Application
compatible	O
with	O
the	O
Bell	O
103	O
de	O
facto	O
standard	O
were	O
commonplace	O
.	O
</s>
<s>
Example	O
models	O
included	O
the	O
Novation	O
CAT	O
and	O
the	O
Anderson-Jacobson	B-Device
.	O
</s>
<s>
A	O
lower-cost	O
option	O
was	O
the	O
Pennywhistle	B-Device
modem	I-Device
,	O
designed	O
to	O
be	O
built	O
using	O
readily	O
available	O
parts	O
.	O
</s>
<s>
Teletype	O
machines	O
were	O
granted	O
access	O
to	O
remote	O
networks	O
such	O
as	O
the	O
Teletypewriter	O
Exchange	O
using	O
the	O
Bell	O
103	O
modem	B-Application
.	O
</s>
<s>
AT&T	O
also	O
produced	O
reduced-cost	O
units	O
,	O
the	O
originate-only	O
113D	O
and	O
the	O
answer-only	O
113B/C	O
modems	B-Application
.	O
</s>
<s>
The	O
201A	O
Data-Phone	O
was	O
a	O
synchronous	O
modem	B-Application
using	O
two-bit-per-symbol	O
phase-shift	B-General_Concept
keying	I-General_Concept
(	O
PSK	O
)	O
encoding	O
,	O
achieving	O
2,000	O
bit/s	O
half-duplex	O
over	O
normal	O
phone	O
lines	O
.	O
</s>
<s>
In	O
November	O
1976	O
,	O
AT&T	O
introduced	O
the	O
212A	O
modem	B-Application
,	O
similar	O
in	O
design	O
,	O
but	O
using	O
the	O
lower	O
frequency	O
set	O
for	O
transmission	O
.	O
</s>
<s>
It	O
was	O
not	O
compatible	O
with	O
the	O
VA3400	O
,	O
but	O
it	O
would	O
operate	O
with	O
103A	O
modem	B-Application
at	O
300bit/s	O
.	O
</s>
<s>
In	O
1977	O
,	O
Vadic	O
responded	O
with	O
the	O
VA3467	O
triple	O
modem	B-Application
,	O
an	O
answer-only	O
modem	B-Application
sold	O
to	O
computer	O
center	O
operators	O
that	O
supported	O
Vadic	O
's	O
1,200	O
-bit/s	O
mode	O
,	O
T	O
's	O
212A	O
mode	O
,	O
and	O
103A	O
operation	O
.	O
</s>
<s>
A	O
significant	O
advance	O
in	O
modems	B-Application
was	O
the	O
Hayes	O
Smartmodem	O
,	O
introduced	O
in	O
1981	O
.	O
</s>
<s>
The	O
Smartmodem	O
was	O
an	O
otherwise	O
standard	O
103A	O
300bit/s	O
direct-connect	O
modem	B-Application
,	O
but	O
it	O
introduced	O
a	O
command	O
language	O
which	O
allowed	O
the	O
computer	O
to	O
make	O
control	O
requests	O
,	O
such	O
as	O
commands	O
to	O
dial	O
or	O
answer	O
calls	O
,	O
over	O
the	O
same	O
RS-232	O
interface	O
used	O
for	O
the	O
data	O
connection	O
.	O
</s>
<s>
The	O
command	O
set	O
used	O
by	O
this	O
device	O
became	O
a	O
de	O
facto	O
standard	O
,	O
the	O
Hayes	B-Device
command	I-Device
set	I-Device
,	O
which	O
was	O
integrated	O
into	O
devices	O
from	O
many	O
other	O
manufacturers	O
.	O
</s>
<s>
Automatic	O
dialing	O
was	O
not	O
a	O
new	O
capability	O
–	O
it	O
had	O
been	O
available	O
via	O
separate	O
Automatic	O
Calling	O
Units	O
,	O
and	O
via	O
modems	B-Application
using	O
the	O
X.21	B-Protocol
interface	O
–	O
but	O
the	O
Smartmodem	O
made	O
it	O
available	O
in	O
a	O
single	O
device	O
that	O
could	O
be	O
used	O
with	O
even	O
the	O
most	O
minimal	O
implementations	O
of	O
the	O
ubiquitous	O
RS-232	O
interface	O
,	O
making	O
this	O
capability	O
accessible	O
from	O
virtually	O
any	O
system	O
or	O
language	O
.	O
</s>
<s>
This	O
eventually	O
led	O
to	O
legal	O
action	O
over	O
use	O
of	O
the	O
patented	O
Hayes	B-Device
command	I-Device
language	O
.	O
</s>
<s>
Dial	O
modems	B-Application
generally	O
remained	O
at	O
300	O
and	O
1,200	O
bit/s	O
(	O
eventually	O
becoming	O
standards	O
such	O
as	O
V.21	O
and	O
V.22	O
)	O
into	O
the	O
mid-1980s	O
.	O
</s>
<s>
Commodore	O
's	O
1982	O
VicModem	O
for	O
the	O
VIC-20	B-Device
was	O
the	O
first	O
modem	B-Application
to	O
be	O
sold	O
under	O
$100	O
,	O
and	O
the	O
first	O
modem	B-Application
to	O
sell	O
a	O
million	O
units	O
.	O
</s>
<s>
By	O
the	O
late	O
1980s	O
,	O
many	O
modems	B-Application
could	O
support	O
improved	O
standards	O
like	O
this	O
,	O
and	O
2,400	O
-bit/s	O
operation	O
was	O
becoming	O
common	O
.	O
</s>
<s>
Increasing	O
modem	B-Application
speed	O
greatly	O
improved	O
the	O
responsiveness	O
of	O
online	O
systems	O
and	O
made	O
file	B-Protocol
transfer	I-Protocol
practical	O
.	O
</s>
<s>
This	O
led	O
to	O
rapid	O
growth	O
of	O
online	O
services	O
with	O
large	O
file	O
libraries	O
,	O
which	O
in	O
turn	O
gave	O
more	O
reason	O
to	O
own	O
a	O
modem	B-Application
.	O
</s>
<s>
The	O
rapid	O
update	O
of	O
modems	B-Application
led	O
to	O
a	O
similar	O
rapid	O
increase	O
in	O
BBS	O
use	O
.	O
</s>
<s>
The	O
introduction	O
of	O
microcomputer	B-Architecture
systems	O
with	O
internal	O
expansion	B-Device
slots	I-Device
made	O
small	O
internal	O
modems	B-Application
practical	O
.	O
</s>
<s>
This	O
led	O
to	O
a	O
series	O
of	O
popular	O
modems	B-Application
for	O
the	O
S-100	B-Architecture
bus	I-Architecture
and	O
Apple	B-Device
II	I-Device
computers	O
that	O
could	O
directly	O
dial	O
out	O
,	O
answer	O
incoming	O
calls	O
,	O
and	O
hang	O
up	O
entirely	O
from	O
software	O
,	O
the	O
basic	O
requirements	O
of	O
a	O
bulletin	B-Application
board	I-Application
system	I-Application
(	O
BBS	O
)	O
.	O
</s>
<s>
The	O
seminal	O
CBBS	B-Protocol
for	O
instance	O
was	O
created	O
on	O
an	O
S-100	O
machine	O
with	O
a	O
Hayes	O
internal	O
modem	B-Application
,	O
and	O
a	O
number	O
of	O
similar	O
systems	O
followed	O
.	O
</s>
<s>
Echo	O
cancellation	O
became	O
a	O
feature	O
of	O
modems	B-Application
in	O
this	O
period	O
,	O
which	O
improved	O
the	O
bandwidth	O
available	O
to	O
both	O
modems	B-Application
by	O
allowing	O
them	O
to	O
ignore	O
their	O
own	O
reflected	O
signals	O
.	O
</s>
<s>
Additional	O
improvements	O
were	O
introduced	O
by	O
quadrature	B-Device
amplitude	I-Device
modulation	I-Device
(	O
QAM	B-Device
)	O
encoding	O
,	O
which	O
increased	O
the	O
number	O
of	O
bits	O
per	O
symbol	O
to	O
four	O
through	O
a	O
combination	O
of	O
phase	O
shift	O
and	O
amplitude	O
.	O
</s>
<s>
While	O
early	O
fax	O
technology	O
also	O
used	O
modulated	B-Application
signals	O
on	O
a	O
phone	O
line	O
,	O
digital	O
fax	O
used	O
the	O
now-standard	O
digital	O
encoding	O
used	O
by	O
computer	B-Application
modems	I-Application
.	O
</s>
<s>
In	O
the	O
early	O
1990s	O
,	O
V.32	O
modems	B-Application
operating	O
at	O
9,600	O
bit/s	O
were	O
introduced	O
,	O
but	O
were	O
expensive	O
and	O
were	O
only	O
starting	O
to	O
enter	O
the	O
market	O
when	O
V.32bis	O
was	O
standardized	O
,	O
which	O
operated	O
at	O
14,400	O
bit/s	O
.	O
</s>
<s>
Rockwell	O
International	O
's	O
chip	O
division	O
developed	O
a	O
new	O
driver	O
chip	B-Device
set	I-Device
incorporating	O
the	O
V.32bis	O
standard	O
and	O
aggressively	O
priced	O
it	O
.	O
</s>
<s>
Supra	O
,	O
Inc	O
.	O
arranged	O
a	O
short-term	O
exclusivity	O
arrangement	O
with	O
Rockwell	O
,	O
and	O
developed	O
the	O
SupraFAXModem	B-Device
14400	I-Device
based	O
on	O
it	O
.	O
</s>
<s>
Introduced	O
in	O
January	O
1992	O
at	O
(	O
or	O
less	O
)	O
,	O
it	O
was	O
half	O
the	O
price	O
of	O
the	O
slower	O
V.32	O
modems	B-Application
already	O
on	O
the	O
market	O
.	O
</s>
<s>
This	O
led	O
to	O
a	O
price	O
war	O
,	O
and	O
by	O
the	O
end	O
of	O
the	O
year	O
V.32	O
was	O
dead	O
,	O
never	O
having	O
been	O
really	O
established	O
,	O
and	O
V.32bis	O
modems	B-Application
were	O
widely	O
available	O
for	O
.	O
</s>
<s>
USRobotics	O
(	O
USR	O
)	O
fought	O
back	O
with	O
a	O
16,800	O
bit/s	O
version	O
of	O
HST	O
,	O
while	O
AT&T	O
introduced	O
a	O
one-off	O
19,200	O
bit/s	O
method	O
they	O
referred	O
to	O
as	O
V.32ter	O
,	O
but	O
neither	O
non-standard	O
modem	B-Application
sold	O
well	O
.	O
</s>
<s>
While	O
waiting	O
,	O
several	O
companies	O
decided	O
to	O
release	O
hardware	B-Architecture
and	O
introduced	O
modems	B-Application
they	O
referred	O
to	O
as	O
V.FAST	O
.	O
</s>
<s>
In	O
order	O
to	O
guarantee	O
compatibility	O
with	O
V.34	O
modems	B-Application
once	O
a	O
standard	O
was	O
ratified	O
(	O
1994	O
)	O
,	O
manufacturers	O
used	O
more	O
flexible	O
components	O
,	O
generally	O
a	O
DSP	B-Architecture
and	O
microcontroller	B-Architecture
,	O
as	O
opposed	O
to	O
purpose-designed	O
ASIC	O
modem	B-Application
chips	O
.	O
</s>
<s>
It	O
employed	O
the	O
most	O
powerful	O
coding	B-General_Concept
techniques	I-General_Concept
available	O
at	O
the	O
time	O
,	O
including	O
channel	O
encoding	O
and	O
shape	O
encoding	O
.	O
</s>
<s>
From	O
the	O
mere	O
four	O
bits	O
per	O
symbol	O
(	O
)	O
,	O
the	O
new	O
standards	O
used	O
the	O
functional	O
equivalent	O
of	O
6	O
to	O
10	O
bits	O
per	O
symbol	O
,	O
plus	O
increasing	O
baud	O
rates	O
from	O
2,400	O
to	O
3	O
,	O
429	O
,	O
to	O
create	O
14.4	O
,	O
28.8	O
,	O
and	O
modems	B-Application
.	O
</s>
<s>
While	O
speeds	O
had	O
been	O
available	O
for	O
leased-line	O
modems	B-Application
for	O
some	O
time	O
,	O
they	O
did	O
not	O
become	O
available	O
for	O
dial	O
up	O
modems	B-Application
until	O
the	O
late	O
1990s	O
.	O
</s>
<s>
The	O
first	O
problem	O
was	O
that	O
the	O
process	O
of	O
analog-to-digital	O
conversion	O
is	O
intrinsically	O
lossy	B-Algorithm
,	O
but	O
second	O
,	O
and	O
more	O
importantly	O
,	O
the	O
digital	O
signals	O
used	O
by	O
the	O
telcos	O
were	O
not	O
"	O
linear	O
"	O
:	O
they	O
did	O
not	O
encode	O
all	O
frequencies	O
the	O
same	O
way	O
,	O
instead	O
utilizing	O
a	O
nonlinear	O
encoding	O
(μ-	O
law	O
and	O
a-law	B-Algorithm
)	O
meant	O
to	O
favor	O
the	O
nonlinear	O
response	O
of	O
the	O
human	O
ear	O
to	O
voice	O
signals	O
.	O
</s>
<s>
Modem	B-Application
manufacturers	O
discovered	O
that	O
,	O
while	O
the	O
analog	O
to	O
digital	O
conversion	O
could	O
not	O
preserve	O
higher	O
speeds	O
,	O
digital-to-analog	O
conversions	O
could	O
.	O
</s>
<s>
Because	O
it	O
was	O
possible	O
for	O
an	O
ISP	O
to	O
obtain	O
a	O
direct	O
digital	O
connection	O
to	O
a	O
telco	O
,	O
a	O
digital	O
modem	B-Application
one	O
that	O
connects	O
directly	O
to	O
a	O
digital	O
telephone	O
network	O
interface	O
,	O
such	O
as	O
T1	B-Protocol
or	O
PRI	O
could	O
send	O
a	O
signal	O
that	O
utilized	O
every	O
bit	O
of	O
bandwidth	O
available	O
in	O
the	O
system	O
.	O
</s>
<s>
The	O
first	O
56k	O
dial-up	O
option	O
was	O
a	O
proprietary	O
design	O
from	O
USRobotics	O
,	O
which	O
they	O
called	O
"	O
X2	O
"	O
because	O
56k	O
was	O
twice	O
the	O
speed	O
( ×2	O
)	O
of	O
28k	O
modems	B-Application
.	O
</s>
<s>
At	O
that	O
time	O
,	O
USRobotics	O
held	O
a	O
40%	O
share	O
of	O
the	O
retail	O
modem	B-Application
market	O
,	O
while	O
Rockwell	O
International	O
held	O
an	O
80%	O
share	O
of	O
the	O
modem	B-Application
chipset	B-Device
market	O
.	O
</s>
<s>
Both	O
technologies	O
reached	O
the	O
market	O
around	O
February	O
1997	O
;	O
although	O
problems	O
with	O
K56Flex	O
modems	B-Application
were	O
noted	O
in	O
product	O
reviews	O
through	O
July	O
,	O
within	O
six	O
months	O
the	O
two	O
technologies	O
worked	O
equally	O
well	O
,	O
with	O
variations	O
dependent	O
largely	O
on	O
local	O
connection	O
characteristics	O
.	O
</s>
<s>
The	O
retail	O
price	O
of	O
these	O
early	O
56K	O
modems	B-Application
was	O
about	O
,	O
compared	O
to	O
for	O
standard	O
33k	O
modems	B-Application
.	O
</s>
<s>
Incompatible	O
with	O
either	O
existing	O
standard	O
,	O
it	O
was	O
an	O
amalgam	O
of	O
both	O
,	O
but	O
was	O
designed	O
to	O
allow	O
both	O
types	O
of	O
modem	B-Application
by	O
a	O
firmware	O
upgrade	O
.	O
</s>
<s>
The	O
V.92	O
standard	O
was	O
approved	O
by	O
ITU	O
in	O
November	O
2000	O
and	O
utilized	O
digital	O
PCM	B-Algorithm
technology	O
to	O
increase	O
the	O
upload	O
speed	O
to	O
a	O
maximum	O
of	O
.	O
</s>
<s>
To	O
avoid	O
this	O
problem	O
,	O
V.92	O
modems	B-Application
offer	O
the	O
option	O
to	O
turn	O
off	O
the	O
digital	O
upstream	O
and	O
instead	O
use	O
a	O
plain	O
33	O
.	O
analog	O
connection	O
in	O
order	O
to	O
maintain	O
a	O
high	O
digital	O
downstream	O
of	O
or	O
higher	O
.	O
</s>
<s>
For	O
a	O
complete	O
list	O
see	O
the	O
companion	O
article	O
list	B-Device
of	I-Device
device	I-Device
bandwidths	I-Device
.	O
</s>
<s>
Many	O
dial-up	B-Application
modems	I-Application
implement	O
standards	O
for	O
data	B-General_Concept
compression	I-General_Concept
to	O
achieve	O
higher	O
effective	O
throughput	O
for	O
the	O
same	O
bitrate	O
.	O
</s>
<s>
As	O
telephone-based	O
56k	O
modems	B-Application
began	O
losing	O
popularity	O
,	O
some	O
Internet	O
service	O
providers	O
such	O
as	O
Netzero/Juno	O
,	O
Netscape	B-Protocol
,	O
and	O
others	O
started	O
using	O
pre-compression	O
to	O
increase	O
apparent	O
throughput	O
.	O
</s>
<s>
This	O
server-side	O
compression	O
can	O
operate	O
much	O
more	O
efficiently	O
than	O
the	O
on-the-fly	O
compression	O
performed	O
within	O
modems	B-Application
,	O
because	O
the	O
compression	B-General_Concept
techniques	I-General_Concept
are	O
content-specific	O
(	O
JPEG	O
,	O
text	O
,	O
EXE	O
,	O
etc	O
.	O
</s>
<s>
)	O
.The	O
drawback	O
is	O
a	O
loss	O
in	O
quality	O
,	O
as	O
they	O
use	O
lossy	B-Algorithm
compression	I-Algorithm
which	O
causes	O
images	O
to	O
become	O
pixelated	O
and	O
smeared	O
.	O
</s>
<s>
These	O
accelerated	O
downloads	O
are	O
integrated	O
into	O
the	O
Opera	B-Application
and	O
Amazon	B-Protocol
Silk	I-Protocol
web	O
browsers	O
,	O
using	O
their	O
own	O
server-side	O
text	O
and	O
image	O
compression	O
requiring	O
all	O
data	O
to	O
pass	O
through	O
their	O
own	O
servers	O
before	O
reaching	O
the	O
user	O
.	O
</s>
<s>
Dial-up	B-Application
modems	I-Application
can	O
attach	O
in	O
two	O
different	O
ways	O
:	O
with	O
an	O
acoustic	B-Device
coupler	I-Device
,	O
or	O
with	O
a	O
direct	O
electrical	O
connection	O
.	O
</s>
<s>
The	O
case	O
Hush-A-Phone	O
Corp	O
.	O
v	O
.	O
United	O
States	O
,	O
which	O
legalized	O
acoustic	B-Device
couplers	I-Device
,	O
applied	O
only	O
to	O
mechanical	O
connections	O
to	O
a	O
telephone	O
set	O
,	O
not	O
electrical	O
connections	O
to	O
the	O
telephone	O
line	O
.	O
</s>
<s>
This	O
opened	O
the	O
door	O
to	O
independent	O
(	O
non-AT	O
&T	O
)	O
manufacture	O
of	O
direct-connect	O
modems	B-Application
,	O
that	O
plugged	O
directly	O
into	O
the	O
phone	O
line	O
rather	O
than	O
via	O
an	O
acoustic	B-Device
coupler	I-Device
.	O
</s>
<s>
While	O
Carterfone	O
required	O
AT&T	O
to	O
permit	O
connection	O
of	O
devices	O
,	O
AT&T	O
successfully	O
argued	O
that	O
they	O
should	O
be	O
allowed	O
to	O
require	O
the	O
use	O
of	O
a	O
special	O
device	O
to	O
protect	O
their	O
network	O
,	O
placed	O
in	O
between	O
the	O
third-party	O
modem	B-Application
and	O
the	O
line	O
,	O
called	O
a	O
Data	B-Architecture
Access	I-Architecture
Arrangement	I-Architecture
or	O
DAA	O
.	O
</s>
<s>
Virtually	O
all	O
modems	B-Application
produced	O
after	O
the	O
1980s	O
are	O
direct-connect	O
.	O
</s>
<s>
While	O
Bell	O
(	O
AT&T	O
)	O
provided	O
modems	B-Application
that	O
attached	O
via	O
direct	O
wire	O
connection	O
to	O
the	O
phone	O
network	O
as	O
early	O
as	O
1958	O
,	O
their	O
regulations	O
at	O
the	O
time	O
did	O
not	O
permit	O
the	O
direct	O
electrical	O
connection	O
of	O
any	O
non-Bell	O
device	O
to	O
a	O
telephone	O
line	O
.	O
</s>
<s>
This	O
allowed	O
third-party	O
(	O
non-Bell	O
)	O
manufacturers	O
to	O
sell	O
modems	B-Application
utilizing	O
an	O
acoustic	B-Device
coupler	I-Device
.	O
</s>
<s>
With	O
an	O
acoustic	B-Device
coupler	I-Device
,	O
an	O
ordinary	O
telephone	O
handset	O
was	O
placed	O
in	O
a	O
cradle	O
containing	O
a	O
speaker	O
and	O
microphone	O
positioned	O
to	O
match	O
up	O
with	O
those	O
on	O
the	O
handset	O
.	O
</s>
<s>
The	O
tones	O
used	O
by	O
the	O
modem	B-Application
were	O
transmitted	O
and	O
received	O
into	O
the	O
handset	O
,	O
which	O
then	O
relayed	O
them	O
to	O
the	O
phone	O
line	O
.	O
</s>
<s>
Because	O
the	O
modem	B-Application
was	O
not	O
electrically	O
connected	O
,	O
it	O
was	O
incapable	O
of	O
picking	O
up	O
,	O
hanging	O
up	O
or	O
dialing	O
,	O
all	O
of	O
which	O
required	O
direct	O
control	O
of	O
the	O
line	O
.	O
</s>
<s>
Early	O
modems	B-Application
could	O
not	O
place	O
or	O
receive	O
calls	O
on	O
their	O
own	O
,	O
but	O
required	O
human	O
intervention	O
for	O
these	O
steps	O
.	O
</s>
<s>
As	O
early	O
as	O
1964	O
,	O
Bell	O
provided	O
automatic	O
calling	O
units	O
that	O
connected	O
separately	O
to	O
a	O
second	O
serial	B-Protocol
port	I-Protocol
on	O
a	O
host	O
machine	O
and	O
could	O
be	O
commanded	O
to	O
open	O
the	O
line	O
,	O
dial	O
a	O
number	O
,	O
and	O
even	O
ensure	O
the	O
far	O
end	O
had	O
successfully	O
connected	O
before	O
transferring	O
control	O
to	O
the	O
modem	B-Application
.	O
</s>
<s>
Eventually	O
this	O
capability	O
would	O
be	O
built	O
into	O
modems	B-Application
and	O
no	O
longer	O
require	O
a	O
separate	O
device	O
.	O
</s>
<s>
Prior	O
to	O
the	O
1990s	O
,	O
modems	B-Application
contained	O
all	O
the	O
electronics	O
and	O
intelligence	O
to	O
convert	O
data	O
in	O
discrete	O
form	O
to	O
an	O
analog	O
(	O
modulated	B-Application
)	O
signal	O
and	O
back	O
again	O
,	O
and	O
to	O
handle	O
the	O
dialing	O
process	O
,	O
as	O
a	O
mix	O
of	O
discrete	O
logic	O
and	O
special-purpose	O
chips	O
.	O
</s>
<s>
This	O
type	O
of	O
modem	B-Application
is	O
sometimes	O
referred	O
to	O
as	O
controller-based	O
.	O
</s>
<s>
In	O
1993	O
,	O
Digicom	O
introduced	O
the	O
Connection	O
96	O
Plus	O
,	O
a	O
modem	B-Application
which	O
replaced	O
the	O
discrete	O
and	O
custom	O
components	O
with	O
a	O
general	O
purpose	O
digital	B-Architecture
signal	I-Architecture
processor	I-Architecture
,	O
which	O
could	O
be	O
reprogrammed	O
to	O
upgrade	O
to	O
newer	O
standards	O
.	O
</s>
<s>
Subsequently	O
,	O
USRobotics	O
released	O
the	O
Sportster	O
Winmodem	O
,	O
a	O
similarly	O
upgradable	O
DSP-based	O
design	O
.	O
</s>
<s>
As	O
this	O
design	O
trend	O
spread	O
,	O
both	O
terms	O
–	O
soft	O
modem	B-Application
and	O
Winmodem	O
–	O
obtained	O
a	O
negative	O
connotation	O
in	O
non-Windows-based	O
computing	O
circles	O
because	O
the	O
drivers	O
were	O
either	O
unavailable	O
for	O
non-Windows	O
platforms	O
,	O
or	O
were	O
only	O
available	O
as	O
unmaintainable	O
closed-source	O
binaries	O
,	O
a	O
particular	O
problem	O
for	O
Linux	O
users	O
.	O
</s>
<s>
Later	O
in	O
the	O
1990s	O
,	O
software-based	O
modems	B-Application
became	O
available	O
.	O
</s>
<s>
These	O
are	O
essentially	O
sound	O
cards	O
,	O
and	O
in	O
fact	O
a	O
common	O
design	O
uses	O
the	O
AC'97	O
audio	O
codec	O
,	O
which	O
provides	O
multichannel	O
audio	O
to	O
a	O
PC	O
and	O
includes	O
three	O
audio	O
channels	O
for	O
modem	B-Application
signals	O
.	O
</s>
<s>
The	O
audio	O
sent	O
and	O
received	O
on	O
the	O
line	O
by	O
a	O
modem	B-Application
of	O
this	O
type	O
is	O
generated	O
and	O
processed	O
entirely	O
in	O
software	O
,	O
often	O
in	O
a	O
device	O
driver	O
.	O
</s>
<s>
There	O
is	O
little	O
functional	O
difference	O
from	O
the	O
user	O
's	O
perspective	O
,	O
but	O
this	O
design	O
reduces	O
the	O
cost	O
of	O
a	O
modem	B-Application
by	O
moving	O
most	O
of	O
the	O
processing	O
power	O
into	O
inexpensive	O
software	O
instead	O
of	O
expensive	O
hardware	B-Architecture
DSPs	B-Architecture
or	O
discrete	O
components	O
.	O
</s>
<s>
Soft	O
modems	B-Application
of	O
both	O
types	O
either	O
are	O
internal	O
cards	O
or	O
connect	O
over	O
external	O
buses	O
such	O
as	O
USB	B-Protocol
.	O
</s>
<s>
Instead	O
,	O
soft	O
modems	B-Application
come	O
with	O
drivers	O
which	O
create	O
an	O
emulated	O
RS-232	O
port	O
,	O
which	O
standard	O
modem	B-Application
software	O
(	O
such	O
as	O
an	O
operating	O
system	O
dialer	O
application	O
)	O
can	O
communicate	O
with	O
.	O
</s>
<s>
"	O
Voice	O
"	O
and	O
"	O
fax	O
"	O
are	O
terms	O
added	O
to	O
describe	O
any	O
dial	O
modem	B-Application
that	O
is	O
capable	O
of	O
recording/playing	O
audio	O
or	O
transmitting/receiving	O
faxes	O
.	O
</s>
<s>
Some	O
modems	B-Application
are	O
capable	O
of	O
all	O
three	O
functions	O
.	O
</s>
<s>
Voice	B-Device
modems	I-Device
are	O
used	O
for	O
computer	O
telephony	O
integration	O
applications	O
as	O
simple	O
as	O
placing/receiving	O
calls	O
directly	O
through	O
a	O
computer	O
with	O
a	O
headset	O
,	O
and	O
as	O
complex	O
as	O
fully	O
automated	O
robocalling	O
systems	O
.	O
</s>
<s>
Fax	O
modems	B-Application
can	O
be	O
used	O
for	O
computer-based	O
faxing	O
,	O
in	O
which	O
faxes	O
are	O
sent	O
and	O
received	O
without	O
inbound	O
or	O
outbound	O
faxes	O
ever	O
needing	O
to	O
ever	O
be	O
printed	O
on	O
paper	O
.	O
</s>
<s>
In	O
a	O
classic	O
example	O
of	O
this	O
setup	O
,	O
each	O
dial-up	B-Application
modem	I-Application
would	O
connect	O
to	O
a	O
modem	B-Application
relay	O
gateway	O
.	O
</s>
<s>
The	O
analog	O
connection	O
from	O
the	O
modem	B-Application
is	O
terminated	O
at	O
the	O
gateway	O
and	O
the	O
signal	O
is	O
demodulated	O
.	O
</s>
<s>
The	O
demodulated	O
control	O
signals	O
are	O
transported	O
over	O
the	O
IP	O
network	O
in	O
an	O
RTP	B-Protocol
packet	O
type	O
defined	O
as	O
State	O
Signaling	O
Events	O
(	O
SSEs	O
)	O
.	O
</s>
<s>
The	O
data	O
from	O
the	O
demodulated	O
signal	O
is	O
sent	O
over	O
the	O
IP	O
network	O
via	O
a	O
transport	O
protocol	O
(	O
also	O
defined	O
as	O
an	O
RTP	B-Protocol
payload	O
)	O
called	O
Simple	O
Packet	O
Relay	O
Transport	O
(	O
SPRT	O
)	O
.	O
</s>
<s>
The	O
gateway	O
at	O
the	O
remote	O
end	O
that	O
receives	O
the	O
packets	O
uses	O
the	O
information	O
to	O
re-modulate	O
the	O
signal	O
for	O
the	O
modem	B-Application
connected	O
at	O
that	O
end	O
.	O
</s>
<s>
While	O
traditionally	O
a	O
hardware	B-Architecture
device	O
,	O
fully	O
software-based	O
modems	B-Application
with	O
the	O
ability	O
to	O
be	O
deployed	O
in	O
a	O
cloud	O
environment	O
(	O
such	O
as	O
Microsoft	B-Application
Azure	I-Application
or	O
AWS	B-Application
)	O
do	O
exist	O
.	O
</s>
<s>
Leveraging	O
a	O
Voice-over-IP	B-Application
(	O
VoIP	B-Application
)	O
connection	O
through	O
a	O
SIP	B-Protocol
Trunk	I-Protocol
,	O
the	O
modulated	B-Application
audio	O
samples	O
are	O
generated	O
and	O
sent	O
over	O
an	O
IP	O
network	O
via	O
RTP	B-Protocol
and	O
an	O
uncompressed	B-General_Concept
audio	O
codec	O
(	O
such	O
as	O
G.711	B-Algorithm
μ-law	B-Algorithm
or	O
a-law	B-Algorithm
)	O
.	O
</s>
<s>
A	O
1994	O
Software	O
Publishers	O
Association	O
found	O
that	O
although	O
60%	O
of	O
computers	O
in	O
US	O
households	O
had	O
a	O
modem	B-Application
,	O
only	O
7%	O
of	O
households	O
went	O
online	O
.	O
</s>
<s>
The	O
United	O
States	O
demographic	O
pattern	O
for	O
dial-up	B-Application
modem	I-Application
users	O
per	O
capita	O
has	O
been	O
more	O
or	O
less	O
mirrored	O
in	O
Canada	O
and	O
Australia	O
for	O
the	O
past	O
20	O
years	O
.	O
</s>
<s>
Dial-up	B-Application
modem	I-Application
use	O
in	O
the	O
US	O
had	O
dropped	O
to	O
60%	O
by	O
2003	O
,	O
and	O
stood	O
at	O
36%	O
in	O
2006	O
.	O
</s>
<s>
Voiceband	O
modems	B-Application
were	O
once	O
the	O
most	O
popular	O
means	O
of	O
Internet	O
access	O
in	O
the	O
US	O
,	O
but	O
with	O
the	O
advent	O
of	O
new	O
ways	O
of	O
accessing	O
the	O
Internet	O
,	O
the	O
traditional	O
56K	O
modem	B-Application
was	O
losing	O
popularity	O
.	O
</s>
<s>
The	O
dial-up	B-Application
modem	I-Application
is	O
still	O
widely	O
used	O
by	O
customers	O
in	O
rural	O
areas	O
where	O
DSL	O
,	O
cable	O
,	O
wireless	O
broadband	B-General_Concept
,	O
satellite	O
,	O
or	O
fiber	B-Application
optic	I-Application
service	O
are	O
either	O
not	O
available	O
or	O
they	O
are	O
unwilling	O
to	O
pay	O
what	O
the	O
available	O
broadband	B-General_Concept
companies	O
charge	O
.	O
</s>
<s>
TDD	O
devices	O
are	O
a	O
subset	O
of	O
the	O
teleprinter	O
intended	O
for	O
use	O
by	O
the	O
deaf	O
or	O
hard	O
of	O
hearing	O
,	O
essentially	O
a	O
small	O
teletype	O
with	O
a	O
built-in	O
dial-up	B-Application
modem	I-Application
and	O
acoustic	B-Device
coupler	I-Device
.	O
</s>
<s>
The	O
first	O
models	O
produced	O
in	O
1964	O
utilized	O
FSK	O
modulation	B-Application
much	O
like	O
early	O
computer	B-Application
modems	I-Application
.	O
</s>
<s>
A	O
leased	B-Architecture
line	I-Architecture
modem	B-Application
also	O
uses	O
ordinary	O
phone	O
wiring	O
,	O
like	O
dial-up	O
and	O
DSL	O
,	O
but	O
does	O
not	O
use	O
the	O
same	O
network	O
topology	O
.	O
</s>
<s>
While	O
dial-up	O
uses	O
a	O
normal	O
phone	O
line	O
and	O
connects	O
through	O
the	O
telephone	O
switching	O
system	O
,	O
and	O
DSL	O
uses	O
a	O
normal	O
phone	O
line	O
but	O
connects	O
to	O
equipment	O
at	O
the	O
telco	O
central	O
office	O
,	O
leased	B-Architecture
lines	I-Architecture
do	O
not	O
terminate	O
at	O
the	O
telco	O
.	O
</s>
<s>
Leased	B-Architecture
lines	I-Architecture
are	O
pairs	O
of	O
telephone	O
wire	O
that	O
have	O
been	O
connected	O
together	O
at	O
one	O
or	O
more	O
telco	O
central	O
offices	O
so	O
that	O
they	O
form	O
a	O
continuous	O
circuit	O
between	O
two	O
subscriber	O
locations	O
,	O
such	O
as	O
a	O
business	O
 '	O
headquarters	O
and	O
a	O
satellite	O
office	O
.	O
</s>
<s>
A	O
dialup	O
modem	B-Application
will	O
not	O
function	O
across	O
this	O
type	O
of	O
line	O
,	O
because	O
it	O
does	O
not	O
provide	O
the	O
power	O
,	O
dialtone	O
and	O
switching	O
that	O
those	O
modems	B-Application
require	O
.	O
</s>
<s>
However	O
,	O
a	O
modem	B-Application
with	O
leased-line	O
capability	O
can	O
operate	O
over	O
such	O
a	O
line	O
,	O
and	O
in	O
fact	O
can	O
have	O
greater	O
performance	O
because	O
the	O
line	O
is	O
not	O
passing	O
through	O
the	O
telco	O
switching	O
equipment	O
,	O
the	O
signal	O
is	O
not	O
filtered	O
,	O
and	O
therefore	O
greater	O
bandwidth	O
is	O
available	O
.	O
</s>
<s>
Leased-line	O
modems	B-Application
can	O
operate	O
in	O
2-wire	O
or	O
4-wire	O
mode	O
.	O
</s>
<s>
When	O
two	O
pairs	O
are	O
available	O
,	O
bandwidth	O
can	O
be	O
as	O
high	O
as	O
1.5	O
Mbit/s	O
,	O
a	O
full	O
data	O
T1	B-Protocol
circuit	I-Protocol
.	O
</s>
<s>
The	O
term	O
broadband	B-General_Concept
was	O
previously	O
used	O
to	O
describe	O
communications	O
faster	O
than	O
what	O
was	O
available	O
on	O
voice	O
grade	O
channels	O
.	O
</s>
<s>
The	O
term	O
broadband	B-General_Concept
gained	O
widespread	O
adoption	O
in	O
the	O
late	O
1990s	O
to	O
describe	O
internet	O
access	O
technology	O
exceeding	O
the	O
56	O
kilobit/s	O
maximum	O
of	O
dialup	O
.	O
</s>
<s>
There	O
are	O
many	O
broadband	B-General_Concept
technologies	O
,	O
such	O
as	O
various	O
DSL	O
(	O
digital	O
subscriber	O
line	O
)	O
technologies	O
and	O
cable	B-Device
broadband	I-Device
.	O
</s>
<s>
Their	O
signals	O
are	O
not	O
sent	O
through	O
ordinary	O
phone	O
exchanges	O
,	O
but	O
are	O
instead	O
received	O
by	O
special	O
equipment	O
(	O
a	O
DSLAM	B-Protocol
)	O
at	O
the	O
telephone	O
company	O
central	O
office	O
.	O
</s>
<s>
Similarly	O
,	O
cable	B-Device
modems	I-Device
use	O
infrastructure	O
originally	O
intended	O
to	O
carry	O
television	O
signals	O
,	O
and	O
like	O
DSL	O
,	O
typically	O
permit	O
receiving	O
television	O
signals	O
at	O
the	O
same	O
time	O
as	O
broadband	B-General_Concept
internet	O
service	O
.	O
</s>
<s>
Other	O
broadband	B-General_Concept
modems	I-General_Concept
include	O
FTTx	B-Architecture
modems	B-Application
,	O
satellite	O
modems	B-Application
,	O
and	O
power	B-Device
line	I-Device
modems	B-Application
.	O
</s>
<s>
Different	O
terms	O
are	O
used	O
for	O
broadband	B-General_Concept
modems	I-General_Concept
,	O
because	O
they	O
frequently	O
contain	O
more	O
than	O
just	O
a	O
modulation/demodulation	O
component	O
.	O
</s>
<s>
Because	O
high-speed	O
connections	O
are	O
frequently	O
used	O
by	O
multiple	O
computers	O
at	O
once	O
,	O
many	O
broadband	B-General_Concept
modems	I-General_Concept
do	O
not	O
have	O
direct	O
(	O
e.g.	O
</s>
<s>
USB	B-Protocol
)	O
PC	O
connections	O
.	O
</s>
<s>
Early	O
broadband	B-General_Concept
modems	I-General_Concept
offered	O
Ethernet	O
handoff	O
allowing	O
the	O
use	O
of	O
one	O
or	O
more	O
public	O
IP	O
addresses	O
,	O
but	O
no	O
other	O
services	O
such	O
as	O
NAT	B-Protocol
and	O
DHCP	O
that	O
would	O
allow	O
multiple	O
computers	O
to	O
share	O
one	O
connection	O
.	O
</s>
<s>
This	O
led	O
to	O
many	O
consumers	O
purchasing	O
separate	O
"	O
broadband	B-Application
routers	I-Application
,	O
"	O
placed	O
between	O
the	O
modem	B-Application
and	O
their	O
network	O
,	O
to	O
perform	O
these	O
functions	O
.	O
</s>
<s>
Eventually	O
,	O
ISPs	O
began	O
providing	O
residential	B-Application
gateways	I-Application
which	O
combined	O
the	O
modem	B-Application
and	O
broadband	B-Application
router	I-Application
into	O
a	O
single	O
package	O
that	O
provided	O
routing	O
,	O
NAT	B-Protocol
,	O
security	O
features	O
,	O
and	O
even	O
Wi-Fi	O
access	O
in	O
addition	O
to	O
modem	B-Application
functionality	O
,	O
so	O
that	O
subscribers	O
could	O
connect	O
their	O
entire	O
household	O
without	O
purchasing	O
any	O
extra	O
equipment	O
.	O
</s>
<s>
Even	O
later	O
,	O
these	O
devices	O
were	O
extended	O
to	O
provide	O
"	O
triple	B-Architecture
play	I-Architecture
"	O
features	O
such	O
as	O
telephony	O
and	O
television	O
service	O
.	O
</s>
<s>
Nonetheless	O
,	O
these	O
devices	O
are	O
still	O
often	O
referred	O
to	O
simply	O
as	O
"	O
modems	B-Application
"	O
by	O
service	O
providers	O
and	O
manufacturers	O
.	O
</s>
<s>
Consequently	O
,	O
the	O
terms	O
"	O
modem	B-Application
"	O
,	O
"	O
router	O
"	O
,	O
and	O
"	O
gateway	O
"	O
are	O
now	O
used	O
interchangeably	O
in	O
casual	O
speech	O
,	O
but	O
in	O
a	O
technical	O
context	O
"	O
modem	B-Application
"	O
may	O
carry	O
a	O
specific	O
connotation	O
of	O
basic	O
functionality	O
with	O
no	O
routing	O
or	O
other	O
features	O
,	O
while	O
the	O
others	O
describe	O
a	O
device	O
with	O
features	O
such	O
as	O
NAT	B-Protocol
.	O
</s>
<s>
Broadband	B-General_Concept
modems	I-General_Concept
may	O
also	O
handle	O
authentication	O
such	O
as	O
PPPoE	B-Protocol
.	O
</s>
<s>
While	O
it	O
is	O
often	O
possible	O
to	O
authenticate	O
a	O
broadband	B-General_Concept
connection	O
from	O
a	O
users	O
PC	O
,	O
as	O
was	O
the	O
case	O
with	O
dial-up	O
internet	O
service	O
,	O
moving	O
this	O
task	O
to	O
the	O
broadband	B-General_Concept
modem	I-General_Concept
allows	O
it	O
to	O
establish	O
and	O
maintain	O
the	O
connection	O
itself	O
,	O
which	O
makes	O
sharing	O
access	O
between	O
PCs	O
easier	O
since	O
each	O
one	O
does	O
not	O
have	O
to	O
authenticate	O
separately	O
.	O
</s>
<s>
Broadband	B-General_Concept
modems	I-General_Concept
typically	O
remain	O
authenticated	O
to	O
the	O
ISP	O
as	O
long	O
as	O
they	O
are	O
powered	O
on	O
.	O
</s>
<s>
Any	O
communication	O
technology	O
sending	O
digital	B-General_Concept
data	I-General_Concept
wirelessly	O
involves	O
a	O
modem	B-Application
.	O
</s>
<s>
This	O
includes	O
direct	O
broadcast	O
satellite	O
,	O
WiFi	O
,	O
WiMax	O
,	O
mobile	O
phones	O
,	O
GPS	O
,	O
Bluetooth	B-Protocol
and	O
NFC	O
.	O
</s>
<s>
Modern	O
telecommunications	O
and	O
data	B-Architecture
networks	I-Architecture
also	O
make	O
extensive	O
use	O
of	O
radio	B-General_Concept
modems	I-General_Concept
where	O
long	O
distance	O
data	O
links	O
are	O
required	O
.	O
</s>
<s>
Such	O
systems	O
are	O
an	O
important	O
part	O
of	O
the	O
PSTN	O
,	O
and	O
are	O
also	O
in	O
common	O
use	O
for	O
high-speed	O
computer	B-Architecture
network	I-Architecture
links	O
to	O
outlying	O
areas	O
where	O
fiber	B-Application
optic	I-Application
is	O
not	O
economical	O
.	O
</s>
<s>
Wireless	B-Device
modems	I-Device
come	O
in	O
a	O
variety	O
of	O
types	O
,	O
bandwidths	O
,	O
and	O
speeds	O
.	O
</s>
<s>
Wireless	B-Device
modems	I-Device
are	O
often	O
referred	O
to	O
as	O
transparent	O
or	O
smart	O
.	O
</s>
<s>
They	O
transmit	O
information	O
that	O
is	O
modulated	B-Application
onto	O
a	O
carrier	O
frequency	O
to	O
allow	O
many	O
wireless	O
communication	O
links	O
to	O
work	O
simultaneously	O
on	O
different	O
frequencies	O
.	O
</s>
<s>
Transparent	O
modems	B-Application
operate	O
in	O
a	O
manner	O
similar	O
to	O
their	O
phone	O
line	O
modem	B-Application
cousins	O
.	O
</s>
<s>
Typically	O
,	O
transparent	O
modems	B-Application
are	O
polled	O
in	O
a	O
round	O
robin	O
manner	O
to	O
collect	O
small	O
amounts	O
of	O
data	O
from	O
scattered	O
locations	O
that	O
do	O
not	O
have	O
easy	O
access	O
to	O
wired	O
infrastructure	O
.	O
</s>
<s>
Transparent	O
modems	B-Application
are	O
most	O
commonly	O
used	O
by	O
utility	O
companies	O
for	O
data	O
collection	O
.	O
</s>
<s>
Smart	O
modems	B-Application
come	O
with	O
media	O
access	O
controllers	O
inside	O
,	O
which	O
prevents	O
random	O
data	O
from	O
colliding	O
and	O
resends	O
data	O
that	O
is	O
not	O
correctly	O
received	O
.	O
</s>
<s>
Smart	O
modems	B-Application
typically	O
require	O
more	O
bandwidth	O
than	O
transparent	O
modems	B-Application
,	O
and	O
typically	O
achieve	O
higher	O
data	O
rates	O
.	O
</s>
<s>
The	O
IEEE	O
802.11	O
standard	O
defines	O
a	O
short	O
range	O
modulation	B-Application
scheme	O
that	O
is	O
used	O
on	O
a	O
large	O
scale	O
throughout	O
the	O
world	O
.	O
</s>
<s>
Modems	B-Application
which	O
use	O
a	O
mobile	O
telephone	O
system	O
(	O
GPRS	B-General_Concept
,	O
UMTS	B-Protocol
,	O
HSPA	O
,	O
EVDO	O
,	O
WiMax	O
,	O
5G	O
etc	O
.	O
</s>
<s>
)	O
,	O
are	O
known	O
as	O
mobile	B-Device
broadband	I-Device
modems	I-Device
(	O
sometimes	O
also	O
called	O
wireless	B-Device
modems	I-Device
)	O
.	O
</s>
<s>
Wireless	B-Device
modems	I-Device
can	O
be	O
embedded	O
inside	O
a	O
laptop	B-Device
,	O
mobile	O
phone	O
or	O
other	O
device	O
,	O
or	O
be	O
connected	O
externally	O
.	O
</s>
<s>
External	O
wireless	B-Device
modems	I-Device
include	O
connect	B-Device
cards	I-Device
,	O
USB	B-Device
modems	I-Device
,	O
and	O
cellular	B-Device
routers	I-Device
.	O
</s>
<s>
Most	O
GSM	O
wireless	B-Device
modems	I-Device
come	O
with	O
an	O
integrated	O
SIM	O
cardholder	O
(	O
i.e.	O
</s>
<s>
Huawei	B-Device
E220	I-Device
,	O
Sierra	O
881	O
.	O
)	O
</s>
<s>
Until	O
the	O
end	O
of	O
April	O
2011	O
,	O
worldwide	O
shipments	O
of	O
USB	B-Device
modems	I-Device
surpassed	O
embedded	O
3G	O
and	O
4G	O
modules	O
by	O
3:1	O
because	O
USB	B-Device
modems	I-Device
can	O
be	O
easily	O
discarded	O
.	O
</s>
<s>
Embedded	O
modems	B-Application
may	O
overtake	O
separate	O
modems	B-Application
as	O
tablet	O
sales	O
grow	O
and	O
the	O
incremental	O
cost	O
of	O
the	O
modems	B-Application
shrinks	O
,	O
so	O
by	O
2016	O
,	O
the	O
ratio	O
may	O
change	O
to	O
1:1	O
.	O
</s>
<s>
Like	O
mobile	O
phones	O
,	O
mobile	B-Device
broadband	I-Device
modems	I-Device
can	O
be	O
SIM	O
locked	O
to	O
a	O
particular	O
network	O
provider	O
.	O
</s>
<s>
Unlocking	O
a	O
modem	B-Application
is	O
achieved	O
the	O
same	O
way	O
as	O
unlocking	O
a	O
phone	O
,	O
by	O
using	O
an	O
'	O
unlock	O
code	O
 '	O
.	O
</s>
<s>
A	O
modem	B-Application
that	O
connects	O
to	O
a	O
fiber	B-Application
optic	I-Application
network	O
is	O
known	O
as	O
an	O
optical	O
network	O
terminal	O
(	O
ONT	O
)	O
or	O
optical	O
network	O
unit	O
(	O
ONU	O
)	O
.	O
</s>
<s>
These	O
are	O
commonly	O
used	O
in	O
fiber	B-Architecture
to	I-Architecture
the	I-Architecture
home	I-Architecture
installations	O
,	O
installed	O
inside	O
or	O
outside	O
a	O
house	O
to	O
convert	O
the	O
optical	O
medium	O
to	O
a	O
copper	O
Ethernet	O
interface	O
,	O
after	O
which	O
a	O
router	O
or	O
gateway	O
is	O
often	O
installed	O
to	O
perform	O
authentication	O
,	O
routing	O
,	O
NAT	B-Protocol
,	O
and	O
other	O
typical	O
consumer	O
internet	O
functions	O
,	O
in	O
addition	O
to	O
"	O
triple	B-Architecture
play	I-Architecture
"	O
features	O
such	O
as	O
telephony	O
and	O
television	O
service	O
.	O
</s>
<s>
Fiber	B-Application
optic	I-Application
systems	O
can	O
use	O
quadrature	B-Device
amplitude	I-Device
modulation	I-Device
to	O
maximize	O
throughput	O
.	O
</s>
<s>
16QAM	B-Device
uses	O
a	O
16-point	O
constellation	O
to	O
send	O
four	O
bits	O
per	O
symbol	O
,	O
with	O
speeds	O
on	O
the	O
order	O
of	O
200	O
or	O
400	O
gigabits	O
per	O
second	O
.	O
</s>
<s>
64QAM	B-Device
uses	O
a	O
64-point	O
constellation	O
to	O
send	O
six	O
bits	O
per	O
symbol	O
,	O
with	O
speeds	O
up	O
to	O
65	O
terabits	O
per	O
second	O
.	O
</s>
<s>
Although	O
the	O
name	O
modem	B-Application
is	O
seldom	O
used	O
,	O
some	O
high-speed	O
home	O
networking	O
applications	O
do	O
use	O
modems	B-Application
,	O
such	O
as	O
powerline	B-Device
ethernet	I-Device
.	O
</s>
<s>
The	O
G.hn	B-General_Concept
standard	O
for	O
instance	O
,	O
developed	O
by	O
ITU-T	O
,	O
provides	O
a	O
high-speed	O
(	O
up	O
to	O
1Gbit/s	O
)	O
local	B-General_Concept
area	I-General_Concept
network	I-General_Concept
using	O
existing	O
home	O
wiring	O
(	O
power	B-Device
lines	I-Device
,	O
phone	O
lines	O
,	O
and	O
coaxial	B-Protocol
cables	I-Protocol
)	O
.	O
</s>
<s>
G.hn	B-General_Concept
devices	O
use	O
orthogonal	B-Protocol
frequency-division	I-Protocol
multiplexing	I-Protocol
(	O
OFDM	B-Protocol
)	O
to	O
modulate	O
a	O
digital	O
signal	O
for	O
transmission	O
over	O
the	O
wire	O
.	O
</s>
<s>
As	O
described	O
above	O
,	O
technologies	O
like	O
Wi-Fi	O
and	O
Bluetooth	B-Protocol
also	O
use	O
modems	B-Application
to	O
communicate	O
over	O
radio	O
at	O
short	O
distances	O
.	O
</s>
<s>
A	O
null	O
modem	B-Application
cable	O
is	O
a	O
specially	O
wired	O
cable	O
connected	O
between	O
the	O
serial	B-Protocol
ports	I-Protocol
of	O
two	O
devices	O
,	O
with	O
the	O
transmit	O
and	O
receive	O
lines	O
reversed	O
.	O
</s>
<s>
It	O
is	O
used	O
to	O
connect	O
two	O
devices	O
directly	O
without	O
a	O
modem	B-Application
.	O
</s>
<s>
The	O
same	O
software	O
or	O
hardware	B-Architecture
typically	O
used	O
with	O
modems	B-Application
(	O
such	O
as	O
Procomm	O
or	O
Minicom	O
)	O
could	O
be	O
used	O
with	O
this	O
type	O
of	O
connection	O
.	O
</s>
<s>
A	O
null	O
modem	B-Application
adapter	O
is	O
a	O
small	O
device	O
with	O
plugs	O
on	O
both	O
end	O
which	O
is	O
placed	O
on	O
the	O
end	O
of	O
a	O
normal	O
"	O
straight-through	O
"	O
serial	O
cable	O
to	O
convert	O
it	O
into	O
a	O
null-modem	O
cable	O
.	O
</s>
<s>
A	O
"	O
short	O
haul	O
modem	B-Application
"	O
is	O
a	O
device	O
that	O
bridges	O
the	O
gap	O
between	O
leased-line	O
and	O
dial-up	B-Application
modems	I-Application
.	O
</s>
<s>
Like	O
a	O
leased-line	O
modem	B-Application
,	O
they	O
transmit	O
over	O
"	O
bare	O
"	O
lines	O
with	O
no	O
power	O
or	O
telco	O
switching	O
equipment	O
,	O
but	O
are	O
not	O
intended	O
for	O
the	O
same	O
distances	O
that	O
leased	B-Architecture
lines	I-Architecture
can	O
achieve	O
.	O
</s>
<s>
Ranges	O
up	O
to	O
several	O
miles	O
are	O
possible	O
,	O
but	O
significantly	O
,	O
short-haul	O
modems	B-Application
can	O
be	O
used	O
for	O
medium	O
distances	O
,	O
greater	O
than	O
the	O
maximum	O
length	O
of	O
a	O
basic	O
serial	O
cable	O
but	O
still	O
relatively	O
short	O
,	O
such	O
as	O
within	O
a	O
single	O
building	O
or	O
campus	O
.	O
</s>
<s>
This	O
allows	O
a	O
serial	O
connection	O
to	O
be	O
extended	O
for	O
perhaps	O
only	O
several	O
hundred	O
to	O
several	O
thousand	O
feet	O
,	O
a	O
case	O
where	O
obtaining	O
an	O
entire	O
telephone	O
or	O
leased	B-Architecture
line	I-Architecture
would	O
be	O
overkill	O
.	O
</s>
<s>
While	O
some	O
short-haul	O
modems	B-Application
do	O
in	O
fact	O
use	O
modulation	B-Application
,	O
low-end	O
devices	O
(	O
for	O
reasons	O
of	O
cost	O
or	O
power	O
consumption	O
)	O
are	O
simple	O
"	O
line	O
drivers	O
"	O
that	O
increase	O
the	O
level	O
of	O
the	O
digital	O
signal	O
but	O
do	O
not	O
modulate	O
it	O
.	O
</s>
<s>
These	O
are	O
not	O
technically	O
modems	B-Application
,	O
but	O
the	O
same	O
terminology	O
is	O
used	O
for	O
them	O
.	O
</s>
