<s>
In	O
optical	O
networking	O
,	O
a	O
lightpath	B-Protocol
is	O
a	O
path	O
between	O
two	O
nodes	O
in	O
an	O
optical	O
network	O
between	O
which	O
light	O
passes	O
through	O
unmodified	O
.	O
</s>
<s>
When	O
a	O
lightpath	B-Protocol
can	O
be	O
established	O
between	O
source	O
and	O
destination	O
node	O
endpoints	O
the	O
connection	O
is	O
totally	O
optical	O
and	O
avoids	O
throttling	O
by	O
intermediate	O
electronic	O
conversions	O
and	O
processing	O
.	O
</s>
<s>
Where	O
a	O
lightpath	B-Protocol
passes	O
through	O
an	O
Optical	B-Protocol
add-drop	I-Protocol
multiplexer	I-Protocol
(	O
OADM	B-Protocol
)	O
is	O
known	O
as	O
a	O
cut-through	O
lightpath	B-Protocol
.	O
</s>
<s>
Where	O
a	O
lightpath	B-Protocol
is	O
added	O
or	O
dropped	O
at	O
an	O
OADM	B-Protocol
,	O
it	O
is	O
known	O
as	O
an	O
added/dropped	O
lightpath	B-Protocol
.	O
</s>
<s>
Where	O
endpoints	O
are	O
connected	O
by	O
a	O
series	O
of	O
lightpaths	B-Protocol
with	O
the	O
intermediate	O
nodes	O
only	O
changing	O
the	O
light	O
wavelength	O
at	O
the	O
junctions	O
this	O
may	O
be	O
referred	O
to	O
as	O
a	O
semi-lightpath	O
.	O
</s>
