<s>
Digital	B-Protocol
Signal	I-Protocol
1	I-Protocol
(	O
DS1	O
,	O
sometimes	O
DS-1	O
)	O
is	O
a	O
T-carrier	O
signaling	O
scheme	O
devised	O
by	O
Bell	O
Labs	O
.	O
</s>
<s>
DS1	O
is	O
the	O
primary	O
digital	O
telephone	O
standard	O
used	O
in	O
the	O
United	O
States	O
,	O
Canada	O
and	O
Japan	O
and	O
is	O
able	O
to	O
transmit	O
up	O
to	O
24	O
multiplexed	B-Architecture
voice	O
and	O
data	O
calls	O
over	O
telephone	O
lines	O
.	O
</s>
<s>
DS1	O
is	O
the	O
logical	O
bit	O
pattern	O
used	O
over	O
a	O
physical	O
T1	B-Protocol
line	I-Protocol
;	O
in	O
practice	O
,	O
the	O
terms	O
DS1	O
and	O
T1	O
are	O
often	O
used	O
interchangeably	O
.	O
</s>
<s>
T1	O
refers	O
to	O
the	O
primary	O
digital	O
telephone	O
carrier	B-Protocol
system	I-Protocol
used	O
in	O
North	O
America	O
.	O
</s>
<s>
T1	O
is	O
one	O
line	O
type	O
of	O
the	O
PCM	B-Algorithm
T-carrier	O
hierarchy	O
.	O
</s>
<s>
T1	O
describes	O
the	O
cabling	O
,	O
signal	O
type	O
,	O
and	O
signal	O
regeneration	O
requirements	O
of	O
the	O
carrier	B-Protocol
system	I-Protocol
.	O
</s>
<s>
The	O
signal	O
transmitted	O
on	O
a	O
T1	B-Protocol
line	I-Protocol
,	O
referred	O
to	O
as	O
the	O
DS1	O
signal	O
,	O
consists	O
of	O
serial	O
bits	O
transmitted	O
at	O
the	O
rate	O
of	O
1.544	O
Mbit/s	O
.	O
</s>
<s>
The	O
type	O
of	O
line	B-Protocol
code	I-Protocol
used	O
is	O
called	O
Alternate	O
Mark	O
Inversion	O
(	O
AMI	O
)	O
.	O
</s>
<s>
Digital	O
Signal	O
Designation	O
is	O
the	O
classification	O
of	O
digital	O
bit	O
rates	O
in	O
the	O
digital	B-Protocol
multiplex	I-Protocol
hierarchy	I-Protocol
used	O
in	O
transport	O
of	O
telephone	O
signals	O
from	O
one	O
location	O
to	O
another	O
.	O
</s>
<s>
DS-1	O
is	O
a	O
communications	O
protocol	O
for	O
multiplexing	B-Architecture
the	O
bitstreams	O
of	O
up	O
to	O
24	O
telephone	O
calls	O
,	O
along	O
with	O
two	O
special	O
bits	O
:	O
a	O
framing	O
bit	O
(	O
for	O
frame	O
synchronization	O
)	O
and	O
a	O
maintenance-signaling	O
bit	O
,	O
transmitted	O
over	O
a	O
digital	O
circuit	B-Protocol
called	O
T1	O
.	O
</s>
<s>
A	O
DS1	O
telecommunication	O
circuit	B-Protocol
multiplexes	B-Protocol
24	O
DS0s	O
.	O
</s>
<s>
The	O
twenty-four	O
DS0s	O
sampled	O
8,000	O
times	O
per	O
second	O
(	O
one	O
8bit	O
PCM	B-Algorithm
sample	O
from	O
each	O
DSO	O
per	O
DS1	O
frame	O
)	O
consume	O
1.536	O
Mbit/s	O
of	O
bandwidth	O
.	O
</s>
<s>
DS1	O
is	O
a	O
full-duplex	O
circuit	B-Protocol
,	O
concurrently	O
transmitting	O
and	O
receiving	O
1.544	O
Mbit/s	O
.	O
</s>
<s>
There	O
are	O
three	O
defined	O
alarm	B-Protocol
indication	I-Protocol
signal	I-Protocol
states	O
,	O
identified	O
by	O
a	O
legacy	O
color	O
scheme	O
:	O
red	O
,	O
yellow	O
and	O
blue	O
.	O
</s>
<s>
The	O
resulting	O
loss	O
of	O
payload	O
data	O
while	O
transmitting	O
a	O
yellow	O
alarm	O
is	O
undesirable	O
,	O
and	O
was	O
resolved	O
in	O
ESF	O
framed	O
signals	O
by	O
using	O
the	O
data	B-Protocol
link	I-Protocol
layer	I-Protocol
.	O
</s>
<s>
Blue	O
alarm	O
,	O
also	O
known	O
as	O
alarm	B-Protocol
indication	I-Protocol
signal	I-Protocol
(	O
AIS	O
)	O
indicates	O
a	O
disruption	O
in	O
the	O
communication	O
path	O
between	O
the	O
terminal	O
equipment	O
and	O
line	O
repeaters	O
or	O
DCS	B-Architecture
.	O
</s>
<s>
The	O
receiving	O
equipment	O
displays	O
a	O
"	O
red	O
alarm	O
"	O
and	O
sends	O
the	O
signal	O
for	O
"	O
yellow	O
alarm	O
"	O
to	O
the	O
far	O
end	O
because	O
it	O
has	O
no	O
framing	O
,	O
but	O
at	O
intermediary	O
interfaces	O
the	O
equipment	O
will	O
report	O
"	O
AIS	O
"	O
or	O
Alarm	B-Protocol
Indication	I-Protocol
Signal	I-Protocol
.	O
</s>
<s>
Additionally	O
,	O
for	O
voice	O
T1s	O
there	O
are	O
two	O
main	O
types	O
:	O
so-called	O
"	O
plain	O
"	O
or	O
Inband	O
T1s	O
and	O
PRI	O
(	O
Primary	B-Protocol
Rate	I-Protocol
Interface	I-Protocol
)	O
.	O
</s>
<s>
Destined	O
successors	O
of	O
the	O
T1	O
system	O
of	O
networks	O
,	O
called	O
T1C	O
,	O
T2	O
,	O
T3	O
,	O
and	O
T4	O
were	O
not	O
a	O
commercial	O
success	O
and	O
disappeared	O
quickly	O
,	O
signals	O
that	O
would	O
have	O
been	O
carried	O
on	O
these	O
systems	O
,	O
called	O
DS1	O
,	O
DS2	O
,	O
DS3	O
,	O
and	O
DS4	B-Protocol
are	O
now	O
carried	O
on	O
T1	O
infrastructure	O
.	O
</s>
<s>
Dark	B-Protocol
fiber	I-Protocol
:	O
Dark	B-Protocol
fiber	I-Protocol
refers	O
to	O
unused	O
fibers	B-Architecture
,	O
available	O
for	O
use	O
.	O
</s>
<s>
Dark	B-Protocol
fiber	I-Protocol
has	O
been	O
,	O
and	O
still	O
is	O
,	O
available	O
for	O
sale	O
on	O
the	O
wholesale	O
market	O
for	O
both	O
metro	O
and	O
wide	O
area	O
links	O
,	O
but	O
it	O
may	O
not	O
be	O
available	O
in	O
all	O
markets	O
or	O
city	O
pairs	O
.	O
</s>
<s>
Dark	B-Protocol
fiber	I-Protocol
capacity	O
is	O
typically	O
used	O
by	O
network	O
operators	O
to	O
build	O
SONET	B-Protocol
and	O
dense	B-Architecture
wavelength	I-Architecture
division	I-Architecture
multiplexing	I-Architecture
(	O
DWDM	O
)	O
networks	O
,	O
usually	O
involving	O
meshes	O
of	O
self-healing	O
rings	O
.	O
</s>
<s>
DS1C	O
is	O
a	O
digital	O
signal	O
equivalent	O
to	O
two	O
Digital	B-Protocol
Signal	I-Protocol
1	I-Protocol
,	O
with	O
extra	O
bits	O
to	O
conform	O
to	O
a	O
signaling	O
standard	O
of	O
3.152	O
Mbit/s	O
.	O
</s>
<s>
Few	O
(	O
if	O
any	O
)	O
of	O
these	O
circuit	B-Protocol
capacities	O
are	O
still	O
in	O
use	O
today	O
.	O
</s>
<s>
In	O
the	O
early	O
days	O
of	O
digital	O
and	O
data	O
transmission	O
,	O
the	O
3-Mbit/s	O
data	O
rate	O
was	O
used	O
to	O
link	O
mainframe	B-Architecture
computers	I-Architecture
together	O
.	O
</s>
<s>
The	O
physical	O
side	O
of	O
this	O
circuit	B-Protocol
is	O
called	O
T1C	O
.	O
</s>
<s>
The	O
T1/E1	B-Protocol
protocol	O
is	O
implemented	O
as	O
a	O
"	O
line	O
interface	O
unit	O
"	O
in	O
silicon	O
.	O
</s>
