<s>
PAROLI	B-Language
is	O
a	O
proprietary	O
protocol	O
used	O
inside	O
a	O
multi-shelf	O
Carrier	B-Protocol
Routing	I-Protocol
System	I-Protocol
from	O
Cisco	O
and	O
stands	O
for	O
"	O
parallel	O
optical	O
link.	O
"	O
</s>
<s>
As	O
the	O
traffic	O
between	O
these	O
kinds	O
of	O
chassis	O
is	O
comparable	O
with	O
the	O
data	O
that	O
flows	O
over	O
a	O
backplane	B-Architecture
in	O
a	O
single-shelf	O
system	O
the	O
required	O
bandwidth	O
is	O
very	O
high	O
and	O
as	O
is	O
the	O
need	O
for	O
reliability	O
the	O
shelves	O
are	O
interconnected	O
using	O
several	O
fibre	B-Architecture
optic	I-Architecture
cables	O
.	O
</s>
<s>
As	O
this	O
protocol/feature	O
is	O
only	O
used	O
in	O
multi-shelf	O
Cisco-CRS	O
systems	O
you	O
will	O
only	O
find	O
it	O
in	O
IOS	B-Device
XR	I-Device
the	O
special	O
high	O
performance	O
version	O
of	O
Cisco	B-Protocol
IOS	I-Protocol
.	O
</s>
<s>
The	O
second	O
option	O
allows	O
for	O
the	O
most	O
fault-tolerant	B-General_Concept
system	I-General_Concept
in	O
a	O
CRS	O
system	O
:	O
although	O
a	O
single	O
shelf	O
switch-fabric	O
allows	O
for	O
redundancy	O
on	O
most	O
levels	O
(	O
power	O
.	O
</s>
<s>
Although	O
the	O
different	O
shelves	O
of	O
a	O
multi-shelf	O
routing	O
system	O
will	O
often	O
be	O
placed	O
directly	O
next	O
to	O
each	O
other	O
the	O
PAROLI	B-Language
system	O
allows	O
for	O
some	O
distance	O
between	O
the	O
shelves	O
.	O
</s>
<s>
in	O
a	O
system	O
with	O
two	O
switch-fabris	O
chassis	O
have	O
one	O
of	O
these	O
chassis	O
with	O
50%	O
of	O
the	O
line-card	O
chassis	O
in	O
dataroom	O
1	O
and	O
the	O
rest	O
of	O
the	O
system	O
in	O
room	O
2	O
so	O
that	O
even	O
when	O
there	O
is	O
fire	O
in	O
one	O
room	O
the	O
system	O
will	O
continue	O
to	O
work	O
)	O
it	O
is	O
possible	O
as	O
long	O
as	O
the	O
length	O
of	O
the	O
fibre-optic	B-Architecture
cables	O
does	O
n't	O
exceed	O
100	O
meters	O
(	O
328feet	O
)	O
.	O
</s>
<s>
The	O
inter	O
shelf	O
communication	O
links	O
will	O
therefore	O
process	O
the	O
same	O
kind	O
of	O
data-volumes	O
as	O
a	O
backplane	B-Architecture
will	O
normally	O
carry	O
in	O
any	O
single-shelf	O
router	O
.	O
</s>
<s>
To	O
allow	O
these	O
speeds	O
via	O
external	O
fibre	B-Architecture
optic	I-Architecture
cabling	O
Cisco	O
designed	O
special	O
modules	O
to	O
make	O
this	O
possible	O
.	O
</s>
