<s>
In	O
modern	O
telephony	O
a	O
remote	B-Architecture
concentrator	I-Architecture
,	O
remote	B-Architecture
concentrator	I-Architecture
unit	I-Architecture
(	O
RCU	O
)	O
,	O
or	O
remote	O
line	O
concentrator	O
(	O
RLC	O
)	O
is	O
a	O
concentrator	O
at	O
the	O
lowest	O
level	O
in	O
the	O
telephone	O
switch	O
hierarchy	O
.	O
</s>
<s>
Only	O
a	O
few	O
hundred	O
telephone	O
lines	O
attach	O
to	O
each	O
remote	B-Architecture
concentrator	I-Architecture
.	O
</s>
<s>
In	O
Europe	O
the	O
buildings	O
which	O
once	O
contained	O
local	O
Strowger	B-Device
switch	I-Device
telephone	O
exchanges	O
are	O
now	O
usually	O
empty	O
except	O
for	O
a	O
remote	B-Architecture
concentrator	I-Architecture
.	O
</s>
<s>
Only	O
call	O
packets	B-Protocol
from	O
or	O
destined	O
to	O
a	O
phone	O
serviced	O
by	O
the	O
concentrator	O
actually	O
are	O
processed	O
by	O
the	O
concentrator	O
—	O
nonlocal	O
phones	O
 '	O
time	O
slots	O
just	O
pass	O
through	O
the	O
concentrator	O
unchanged	O
.	O
</s>
<s>
The	O
interface	O
between	O
remote	B-Architecture
concentrators	I-Architecture
and	O
their	O
parent	O
telephone	O
switches	O
has	O
been	O
standardised	O
by	O
ETSI	O
as	O
the	O
V5	B-Protocol
interface	I-Protocol
.	O
</s>
<s>
Concentrators	O
are	O
often	O
placed	O
alongside	O
a	O
digital	B-Protocol
subscriber	I-Protocol
line	I-Protocol
access	I-Protocol
multiplexer	I-Protocol
(	O
DSLAM	B-Protocol
)	O
.	O
</s>
<s>
This	O
can	O
provide	O
access	O
to	O
asymmetric	O
digital	O
subscriber	B-Architecture
line	I-Architecture
(	O
ADSL	O
)	O
Internet	O
service	O
for	O
subscribers	O
who	O
are	O
beyond	O
the	O
normal	O
signaling	O
limit	O
on	O
a	O
copper	O
wire	O
loop	O
.	O
</s>
<s>
For	O
example	O
,	O
a	O
fiber	O
optic	O
cable	O
might	O
run	O
up	O
to	O
without	O
a	O
repeater	O
from	O
the	O
telephone	O
exchange	O
to	O
a	O
concentrator	O
site	O
,	O
and	O
local	O
subscriber	O
wire	O
local	B-Architecture
loops	I-Architecture
can	O
extend	O
an	O
additional	O
4km	O
beyond	O
the	O
concentrator	O
and	O
its	O
DSLAM	B-Protocol
.	O
</s>
