<s>
A	O
dark	B-Protocol
fibre	I-Protocol
or	O
unlit	B-Protocol
fibre	I-Protocol
is	O
an	O
unused	O
optical	B-Architecture
fibre	I-Architecture
,	O
available	O
for	O
use	O
in	O
fibre-optic	B-Application
communication	I-Application
.	O
</s>
<s>
Dark	B-Protocol
fibre	I-Protocol
may	O
be	O
leased	O
from	O
a	O
network	O
service	O
provider	O
.	O
</s>
<s>
Dark	B-Protocol
fibre	I-Protocol
originally	O
referred	O
to	O
the	O
potential	O
network	O
capacity	O
of	O
telecommunication	O
infrastructure	O
.	O
</s>
<s>
Because	O
the	O
marginal	O
cost	O
of	O
installing	O
additional	O
fibre	B-Architecture
optic	I-Architecture
cables	O
is	O
very	O
low	O
once	O
a	O
trench	O
has	O
been	O
dug	O
or	O
conduit	O
laid	O
,	O
a	O
great	O
excess	O
of	O
fibre	O
was	O
installed	O
in	O
the	O
US	O
during	O
the	O
telecom	O
boom	O
of	O
the	O
late	O
1990s	O
and	O
early	O
2000s	O
.	O
</s>
<s>
This	O
excess	O
capacity	O
was	O
later	O
referred	O
to	O
as	O
dark	B-Protocol
fibre	I-Protocol
following	O
the	O
dot-com	O
crash	O
of	O
the	O
early	O
2000s	O
that	O
briefly	O
reduced	O
demand	O
for	O
high-speed	O
data	O
transmission	O
.	O
</s>
<s>
These	O
unused	O
fibre	B-Architecture
optic	I-Architecture
cables	O
later	O
created	O
a	O
new	O
market	O
for	O
unique	O
private	O
services	O
that	O
could	O
not	O
be	O
accommodated	O
on	O
lit	O
fibre	O
cables	O
(	O
i.e.	O
,	O
cables	O
used	O
in	O
traditional	O
long-distance	O
communication	O
)	O
.	O
</s>
<s>
Many	O
fibre-optic	B-Architecture
cable	O
owners	O
such	O
as	O
railroads	O
and	O
power	O
utilities	O
have	O
always	O
included	O
additional	O
fibres	O
with	O
the	O
intention	O
to	O
lease	O
these	O
to	O
other	O
carriers	O
.	O
</s>
<s>
The	O
advent	O
of	O
wavelength-division	B-Architecture
multiplexing	I-Architecture
reduced	O
the	O
demand	O
for	O
fibre	O
by	O
increasing	O
the	O
capacity	O
of	O
a	O
single	O
fibre	O
by	O
a	O
factor	O
of	O
as	O
much	O
as	O
100	O
.	O
</s>
<s>
According	O
to	O
Gerry	O
Butters	O
,	O
the	O
former	O
head	O
of	O
Lucent	O
's	O
Optical	O
Networking	O
Group	O
at	O
Bell	O
Labs	O
,	O
the	O
amount	O
of	O
data	O
that	O
could	O
be	O
carried	O
by	O
an	O
optical	B-Architecture
fibre	I-Architecture
was	O
doubling	O
every	O
nine	O
months	O
at	O
the	O
time	O
.	O
</s>
<s>
For	O
many	O
years	O
incumbent	O
local	O
exchange	O
carriers	O
would	O
not	O
sell	O
dark	B-Protocol
fibre	I-Protocol
to	O
end	O
users	O
,	O
because	O
they	O
believed	O
selling	O
access	O
to	O
this	O
core	O
asset	O
would	O
cannibalize	O
their	O
other	O
,	O
more	O
lucrative	O
services	O
.	O
</s>
<s>
Incumbent	O
carriers	O
in	O
the	O
United	O
States	O
were	O
required	O
to	O
sell	O
dark	B-Protocol
fibre	I-Protocol
to	O
competitive	O
local	O
exchange	O
carriers	O
as	O
unbundled	B-Architecture
network	I-Architecture
elements	I-Architecture
(	O
UNE	O
)	O
,	O
but	O
they	O
have	O
successfully	O
lobbied	O
to	O
reduce	O
these	O
provisions	O
for	O
existing	O
fibre	O
,	O
and	O
eliminated	O
it	O
completely	O
for	O
new	O
fibre	O
placed	O
for	O
fibre	B-Architecture
to	I-Architecture
the	I-Architecture
premises	I-Architecture
(	O
FTTP	B-Architecture
)	O
deployments	O
.	O
</s>
<s>
Meanwhile	O
,	O
other	O
companies	O
arose	O
specializing	O
as	O
dark	B-Protocol
fibre	I-Protocol
providers	O
.	O
</s>
<s>
Dark	B-Protocol
fibre	I-Protocol
became	O
more	O
available	O
when	O
there	O
was	O
enormous	O
overcapacity	O
after	O
the	O
telecoms	O
boom	O
years	O
of	O
the	O
late	O
1990s	O
through	O
2001	O
.	O
</s>
<s>
The	O
market	O
for	O
dark	B-Protocol
fibre	I-Protocol
tightened	O
up	O
with	O
the	O
return	O
of	O
capital	O
investment	O
to	O
light	O
up	O
existing	O
fibre	O
,	O
and	O
with	O
mergers	O
and	O
acquisitions	O
resulting	O
in	O
a	O
consolidation	O
of	O
dark	B-Protocol
fibre	I-Protocol
providers	O
.	O
</s>
<s>
Dark	B-Protocol
fibre	I-Protocol
can	O
be	O
used	O
to	O
create	O
a	O
privately	O
operated	O
optical	B-Architecture
fibre	I-Architecture
network	O
that	O
is	O
run	O
directly	O
by	O
its	O
operator	O
over	O
dark	B-Protocol
fibre	I-Protocol
leased	O
or	O
purchased	O
from	O
another	O
supplier	O
.	O
</s>
<s>
This	O
is	O
opposed	O
to	O
purchasing	O
bandwidth	O
or	O
leased	B-Architecture
line	I-Architecture
capacity	O
on	O
an	O
existing	O
network	O
.	O
</s>
<s>
Dark	B-Protocol
fibre	I-Protocol
networks	I-Protocol
may	O
be	O
used	O
for	O
private	O
networking	O
,	O
or	O
as	O
Internet	O
access	O
or	O
Internet	B-Architecture
infrastructure	I-Architecture
networking	O
.	O
</s>
<s>
Dark	B-Protocol
fibre	I-Protocol
networks	I-Protocol
may	O
be	O
point-to-point	O
,	O
or	O
use	O
star	B-Architecture
,	O
self-healing	O
ring	O
,	O
or	O
mesh	B-Architecture
topologies	I-Architecture
.	O
</s>
<s>
Because	O
both	O
ends	O
of	O
the	O
link	O
are	O
controlled	O
by	O
the	O
same	O
organization	O
,	O
dark	B-Protocol
fibre	I-Protocol
networks	I-Protocol
can	O
operate	O
using	O
the	O
latest	O
optical	O
protocols	O
using	O
wavelength	B-Architecture
division	I-Architecture
multiplexing	I-Architecture
to	O
add	O
capacity	O
where	O
needed	O
,	O
and	O
to	O
provide	O
an	O
upgrade	O
path	O
between	O
technologies	O
.	O
</s>
<s>
Many	O
dark	B-Protocol
fibre	I-Protocol
metropolitan	O
area	O
networks	O
use	O
cheap	O
Gigabit	O
Ethernet	O
equipment	O
over	O
CWDM	O
,	O
rather	O
than	O
expensive	O
SONET	B-Protocol
ring	I-Protocol
systems	O
.	O
</s>
<s>
They	O
offer	O
very	O
high	O
price-performance	O
for	O
network	O
users	O
who	O
require	O
high	O
performance	O
,	O
such	O
as	O
Google	B-Application
,	O
which	O
has	O
dark	O
network	O
capacities	O
for	O
video	O
and	O
search	O
data	O
,	O
or	O
wish	O
to	O
operate	O
their	O
own	O
network	O
for	O
security	O
or	O
other	O
commercial	O
reasons	O
.	O
</s>
<s>
However	O
,	O
dark	B-Protocol
fibre	I-Protocol
networks	I-Protocol
are	O
generally	O
only	O
available	O
in	O
high-population-density	O
areas	O
where	O
fibre	O
has	O
already	O
been	O
laid	O
,	O
as	O
the	O
civil	O
engineering	O
costs	O
of	O
installing	O
fibre	O
to	O
new	O
locations	O
is	O
often	O
prohibitive	O
.	O
</s>
<s>
For	O
these	O
reasons	O
,	O
dark	B-Protocol
fibre	I-Protocol
networks	I-Protocol
are	O
typically	O
run	O
between	O
data	B-Operating_System
centres	I-Operating_System
and	O
other	O
places	O
with	O
existing	O
fibre	O
infrastructure	O
.	O
</s>
<s>
Managed	B-Protocol
dark	I-Protocol
fibre	I-Protocol
is	O
a	O
form	O
of	O
wavelength-division	B-Architecture
multiplexed	I-Architecture
access	O
to	O
otherwise	O
dark	B-Protocol
fibre	I-Protocol
where	O
a	O
pilot	O
signal	O
is	O
beamed	O
into	O
the	O
fibre	O
by	O
the	O
fibre	O
provider	O
for	O
management	O
purposes	O
using	O
a	O
transponder	O
tuned	O
to	O
an	O
assigned	O
wavelength	O
.	O
</s>
<s>
Virtual	O
dark	B-Protocol
fibre	I-Protocol
using	O
wavelength	B-Architecture
multiplexing	I-Architecture
allows	O
a	O
service	O
provider	O
to	O
offer	O
individual	O
wavelengths	O
.	O
</s>
<s>
This	O
is	O
typically	O
done	O
using	O
coarse	B-Architecture
wavelength	I-Architecture
division	I-Architecture
multiplexing	I-Architecture
CWDM	O
because	O
the	O
wider	O
20nm	O
spacing	O
of	O
the	O
wavebands	O
makes	O
these	O
systems	O
much	O
less	O
susceptible	O
to	O
interference	O
.	O
</s>
