<s>
Optical	B-Protocol
IP	I-Protocol
Switching	I-Protocol
(	O
OIS	O
)	O
,	O
is	O
a	O
novel	O
method	O
of	O
creating	O
transparent	O
optical	O
connections	O
between	O
network	O
nodes	O
using	O
a	O
flow-based	O
approach	O
.	O
</s>
<s>
An	O
IP	B-Protocol
flow	O
is	O
a	O
collection	O
of	O
IP	B-Protocol
packets	O
going	O
from	O
the	O
same	O
source	O
to	O
the	O
same	O
destination	O
:	O
the	O
exchange	O
of	O
IP	B-Protocol
packets	O
is	O
the	O
mechanism	O
that	O
allows	O
the	O
transport	O
of	O
information	O
over	O
the	O
Internet	O
.	O
</s>
<s>
However	O
,	O
since	O
a	O
flow	O
is	O
defined	O
as	O
a	O
sequence	O
of	O
packets	O
going	O
from	O
the	O
same	O
source	O
to	O
the	O
same	O
destination	O
,	O
if	O
the	O
router	O
recognises	O
the	O
flow	O
it	O
could	O
create	O
a	O
short-cut	O
by	O
creating	O
a	O
“	O
switched	O
”	O
connection	O
allowing	O
all	O
the	O
packets	O
belonging	O
to	O
the	O
same	O
IP	B-Protocol
flow	O
to	O
proceed	O
directly	O
towards	O
the	O
correct	O
direction	O
without	O
being	O
analyzed	O
one	O
after	O
the	O
other	O
.	O
</s>
<s>
This	O
general	O
idea	O
is	O
known	O
as	O
IP	B-Protocol
switching	O
.	O
</s>
<s>
If	O
the	O
shortcut	O
however	O
occurs	O
at	O
an	O
optical	O
level	O
,	O
the	O
process	O
becomes	O
Optical	B-Protocol
IP	I-Protocol
Switching	I-Protocol
.	O
</s>
<s>
The	O
advantage	O
of	O
OIS	O
comes	O
from	O
the	O
fact	O
that	O
today	O
packets	O
are	O
transmitted	O
optically	O
between	O
two	O
points	O
but	O
at	O
each	O
routing	O
station	O
they	O
have	O
to	O
be	O
converted	O
into	O
electrical	O
signal	O
,	O
routed	O
and	O
converted	O
back	O
into	O
optical	O
to	O
continue	O
their	O
travel	O
over	O
the	O
optical	B-Architecture
fiber	I-Architecture
.	O
</s>
<s>
A	O
basic	O
implementation	O
of	O
the	O
OIS	O
concept	O
sees	O
an	O
optical	O
router	O
that	O
monitors	O
IP	B-Protocol
traffic	O
and	O
if	O
a	O
flow	O
appears	O
with	O
specific	O
characteristics	O
the	O
router	O
establishes	O
an	O
optical	O
cut-through	O
path	O
between	O
its	O
upstream	O
and	O
downstream	O
neighbours	O
,	O
requesting	O
the	O
upstream	O
node	O
to	O
place	O
all	O
the	O
packets	O
belonging	O
to	O
the	O
flow	O
into	O
the	O
new	O
path	O
.	O
</s>
<s>
The	O
newly	O
generated	O
trail	O
bypasses	O
the	O
IP	B-Protocol
layer	O
of	O
the	O
router	O
,	O
as	O
the	O
packets	O
transparently	O
flow	O
from	O
the	O
upstream	O
to	O
the	O
downstream	O
neighbour	O
.	O
</s>
<s>
For	O
this	O
reason	O
,	O
aggregating	O
more	O
IP	B-Protocol
flows	O
into	O
the	O
same	O
dedicated	O
path	O
is	O
essential	O
for	O
the	O
performance	O
of	O
an	O
OIS	O
network	O
.	O
</s>
<s>
The	O
aggregation	O
introduces	O
a	O
trade-off	O
between	O
the	O
number	O
of	O
IP	B-Protocol
flows	O
that	O
can	O
be	O
aggregated	O
together	O
and	O
the	O
length	O
of	O
the	O
optical	O
trail	O
that	O
accommodates	O
them	O
.	O
</s>
<s>
A	O
core	O
node	O
implementing	O
optical	B-Protocol
IP	I-Protocol
switching	I-Protocol
must	O
be	O
endowed	O
with	O
electrical	O
processing	O
and	O
memory	O
resources	O
(	O
as	O
a	O
standard	O
IP	B-Protocol
router	O
)	O
,	O
a	O
variable	O
number	O
of	O
optical	O
transceivers	O
and	O
an	O
optical	O
switching	O
element	O
(	O
usually	O
a	O
MEMS	B-Architecture
based	O
device	O
)	O
.	O
</s>
