<s>
In	O
telecommunications	O
,	O
common	B-Device
control	I-Device
is	O
a	O
principle	O
of	O
switching	O
telephone	O
calls	O
in	O
an	O
automatic	O
telephone	O
exchange	O
that	O
employs	O
shared	O
control	O
equipment	O
which	O
is	O
attached	O
to	O
the	O
circuit	O
of	O
a	O
call	O
only	O
for	O
the	O
duration	O
of	O
establishing	O
or	O
otherwise	O
controlling	O
the	O
call	O
.	O
</s>
<s>
Strowger	B-Device
exchanges	I-Device
are	O
usually	O
direct	O
control	O
systems	O
,	O
whereas	O
crossbar	O
,	O
and	O
electronic	O
exchanges	O
(	O
including	O
all	O
stored	B-Device
program	I-Device
control	I-Device
systems	O
)	O
are	O
common	B-Device
control	I-Device
systems	O
.	O
</s>
<s>
Common	B-Device
control	I-Device
is	O
also	O
known	O
as	O
indirect	O
control	O
or	O
register	O
control	O
.	O
</s>
<s>
Early	O
semi-mechanical	O
installations	O
with	O
common	B-Device
control	I-Device
components	O
existed	O
,	O
for	O
example	O
rotary	B-Device
systems	I-Device
in	O
Sweden	O
and	O
France	O
in	O
1915	O
,	O
and	O
the	O
first	O
panel	O
switches	O
in	O
Newark	O
,	O
New	O
Jersey	O
,	O
also	O
in	O
1915	O
.	O
</s>
<s>
The	O
first	O
large-scale	O
,	O
fully	O
automatic	O
,	O
common	B-Device
control	I-Device
switching	O
system	O
deployed	O
in	O
commercial	O
production	O
service	O
was	O
the	O
ATlantic	O
central	O
office	O
in	O
Omaha	O
,	O
Nebraska	O
,	O
a	O
panel	O
system	O
cut	O
over	O
on	O
December	O
10	O
,	O
1921	O
.	O
</s>
<s>
In	O
1922	O
,	O
common	B-Device
control	I-Device
was	O
introduced	O
in	O
Strowger-type	B-Device
step-by-step	O
systems	O
,	O
resulting	O
in	O
the	O
first	O
installations	O
of	O
Director	O
systems	O
in	O
Havanna	O
,	O
Cuba	O
in	O
1924	O
,	O
and	O
in	O
London	O
,	O
England	O
in	O
1927	O
.	O
</s>
<s>
By	O
the	O
mid-1920s	O
,	O
common	B-Device
control	I-Device
ideas	O
had	O
extended	O
to	O
include	O
marker	B-Device
systems	O
for	O
testing	O
for	O
idle	O
trunks	O
.	O
</s>
<s>
During	O
the	O
1960s	O
,	O
common	B-Device
control	I-Device
exchanges	O
became	O
stored	B-Device
program	I-Device
control	I-Device
exchanges	I-Device
,	O
and	O
by	O
the	O
1970s	O
they	O
used	O
common-channel	O
signaling	O
in	O
which	O
the	O
channels	O
that	O
are	O
used	O
for	O
signaling	O
are	O
not	O
used	O
for	O
message	O
traffic	O
(	O
out	O
of	O
band	O
signaling	O
)	O
.	O
</s>
