<s>
Alarm	B-Protocol
indication	I-Protocol
signal	I-Protocol
(	O
AIS	O
)	O
(	O
also	O
called	O
“	O
all	O
ones	O
”	O
because	O
of	O
the	O
data	O
and	O
framing	O
pattern	O
)	O
is	O
a	O
signal	O
transmitted	O
by	O
an	O
intermediate	O
element	O
of	O
a	O
multi-node	O
transport	O
circuit	O
that	O
is	O
part	O
of	O
a	O
concatenated	O
telecommunications	O
system	O
to	O
alert	O
the	O
receiving	O
end	O
of	O
the	O
circuit	O
that	O
a	O
segment	O
of	O
the	O
end-to-end	O
link	O
has	O
failed	O
at	O
a	O
logical	O
or	O
physical	O
level	O
,	O
even	O
if	O
the	O
system	O
it	O
is	O
directly	O
connected	O
to	O
is	O
still	O
working	O
.	O
</s>
<s>
When	O
an	O
element	O
of	O
T1	O
or	O
(	O
DS1	B-Protocol
)	O
circuit	O
loses	O
signal	O
(	O
LOS	O
)	O
or	O
framing	O
(	O
OOF	O
)	O
,	O
the	O
device	O
replaces	O
the	O
erroneous	O
data	O
bits	O
with	O
a	O
series	O
of	O
ones	O
.	O
</s>
<s>
These	O
are	O
SONET	B-Protocol
OC-xx	O
level	O
indications	O
that	O
indicate	O
if	O
the	O
errored	O
element	O
is	O
in	O
a	O
section	O
,	O
segment	O
,	O
line	O
segment	O
,	O
or	O
path	O
segment	O
of	O
the	O
SONET	B-Protocol
circuit	O
.	O
</s>
<s>
Middle	O
20th	O
century	O
analog	O
carrier	B-Protocol
systems	I-Protocol
had	O
Carrier	O
Group	O
Alarms	O
by	O
which	O
the	O
failure	O
of	O
a	O
pilot	O
signal	O
was	O
alerted	O
to	O
telephone	O
exchange	O
equipment	O
,	O
imposing	O
an	O
automated	O
make-busy	O
condition	O
so	O
the	O
trunks	O
carried	O
by	O
the	O
failed	O
system	O
would	O
not	O
be	O
used	O
.	O
</s>
<s>
The	O
improved	O
AIS	O
originated	O
with	O
the	O
T-carrier	O
system	O
,	O
and	O
became	O
a	O
standard	O
feature	O
of	O
subsequent	O
plesiochronous	B-Architecture
and	O
synchronous	O
circuit-based	O
communication	O
systems	O
,	O
and	O
is	O
also	O
part	O
of	O
the	O
Asynchronous	O
Transfer	O
Mode	O
standards	O
.	O
</s>
<s>
As	O
the	O
use	O
of	O
Ethernet	O
for	O
long-distance	O
data	O
links	O
has	O
increased	O
,	O
the	O
need	O
for	O
a	O
similar	O
end-to-end	O
OA&M	B-Architecture
function	O
has	O
led	O
to	O
the	O
development	O
of	O
a	O
similar	O
Ethernet	O
alarm	B-Protocol
indication	I-Protocol
signal	I-Protocol
(	O
EthAIS	O
)	O
.	O
</s>
