<s>
SITOR	B-Device
(	O
SImplex	O
Teletype	O
Over	O
Radio	O
)	O
is	O
a	O
system	O
for	O
transmitting	O
text	O
messages	O
.	O
</s>
<s>
Although	O
it	O
uses	O
the	O
same	O
frequency-shift	O
keying	O
(	O
FSK	O
)	O
modulation	O
used	O
by	O
regular	O
RTTY	O
,	O
SITOR	B-Device
uses	O
error	B-Error_Name
detection	I-Error_Name
,	O
redundancy	O
,	O
and/or	O
retransmission	O
to	O
improve	O
reliability	O
.	O
</s>
<s>
There	O
are	O
two	O
SITOR	B-Device
modes	O
:	O
</s>
<s>
SITOR-A	B-Device
is	O
used	O
for	O
point	O
to	O
point	O
links	O
.	O
</s>
<s>
SITOR-A	B-Device
uses	O
automatic	B-Error_Name
repeat	I-Error_Name
request	I-Error_Name
(	O
ARQ	O
)	O
to	O
gain	O
reliability	O
.	O
</s>
<s>
SITOR-B	B-Device
is	O
used	O
for	O
broadcast	B-Operating_System
links	O
.	O
</s>
<s>
SITOR-B	B-Device
transmits	O
each	O
character	O
in	O
a	O
message	O
twice	O
to	O
gain	O
reliability	O
.	O
</s>
<s>
SITOR-B	B-Device
by	O
definition	O
uses	O
forward	B-Error_Name
error	I-Error_Name
correction	I-Error_Name
(	O
FEC	O
)	O
,	O
versus	O
ARQ	O
for	O
SITOR-A	B-Device
.	O
</s>
<s>
SITOR	B-Device
sends	O
7-bit	O
characters	O
as	O
a	O
bit	O
stream	O
at	O
100	O
baud	O
(	O
which	O
,	O
in	O
this	O
case	O
,	O
is	O
100	O
bits	O
per	O
second	O
,	O
10	O
milliseconds	O
per	O
bit	O
,	O
or	O
70	O
milliseconds	O
per	O
character	O
)	O
.	O
</s>
<s>
SITOR	B-Device
is	O
used	O
commonly	O
on	O
shortwave	O
bands	O
,	O
where	O
it	O
is	O
used	O
to	O
transmit	O
maritime-related	O
information	O
such	O
as	O
weather	O
forecasts	O
and	O
storm	O
warnings	O
.	O
</s>
<s>
SITOR-B	B-Device
is	O
used	O
for	O
narrow-band	O
direct	O
printing	O
(	O
NBDP	O
)	O
.	O
</s>
<s>
NAVTEX	O
marine	O
weather	O
and	O
safety	O
messages	O
are	O
broadcast	B-Operating_System
using	O
SITOR-B	B-Device
.	O
</s>
<s>
(	O
NAVTEX	O
is	O
layered	O
on	O
top	O
of	O
SITOR-B	B-Device
just	O
as	O
HTML	O
is	O
layered	O
on	O
top	O
of	O
TCP	O
.	O
)	O
</s>
<s>
Amateur	O
radio	O
uses	O
SITOR	B-Device
but	O
calls	O
it	O
AMTOR	B-Device
,	O
AMateur	O
Teleprinting	O
Over	O
Radio	O
.	O
</s>
<s>
AMTOR-A	O
is	O
SITOR-A	B-Device
.	O
</s>
<s>
AMTOR-B	O
(	O
also	O
called	O
AMTOR-FEC	O
)	O
is	O
SITOR-B	B-Device
.	O
</s>
<s>
In	O
1991	O
,	O
an	O
AMTOR	B-Device
extension	O
was	O
described	O
that	O
includes	O
lower	O
case	O
and	O
other	O
printable	O
ASCII	O
characters	O
.	O
</s>
<s>
SITOR	B-Device
recasts	O
ITA2	O
into	O
a	O
7bit	O
code	O
called	O
CCIR	O
476	O
.	O
</s>
<s>
SITOR	B-Device
uses	O
the	O
additional	O
code	O
points	O
for	O
idle	O
,	O
phasing	O
,	O
and	O
repeat	O
requests	O
.	O
</s>
<s>
SITOR	B-Device
has	O
an	O
aurally	O
easy	O
to	O
identify	O
idling	O
pattern	O
.	O
</s>
