<s>
Shared	B-Architecture
risk	I-Architecture
resource	I-Architecture
group	I-Architecture
(	O
commonly	O
referred	O
to	O
as	O
shared	O
risk	O
group	O
or	O
SRG	O
)	O
is	O
a	O
concept	O
in	O
optical	B-Protocol
mesh	I-Protocol
network	I-Protocol
routing	O
that	O
different	O
networks	O
may	O
suffer	O
from	O
a	O
common	O
failure	O
if	O
they	O
share	O
a	O
common	O
risk	O
or	O
a	O
common	O
SRG	O
.	O
</s>
<s>
SRG	O
is	O
not	O
limited	O
to	O
Optical	B-Protocol
mesh	I-Protocol
networks	I-Protocol
:	O
SRGs	O
are	O
also	O
used	O
in	O
MPLS	B-Protocol
,	O
IP	B-Protocol
networks	I-Protocol
,	O
and	O
synchronous	B-Protocol
optical	I-Protocol
networks	I-Protocol
.	O
</s>
<s>
The	O
MPLS	B-Protocol
as	O
well	O
as	O
the	O
IP	B-Protocol
network	I-Protocol
uses	O
the	O
high	O
speed	O
capabilities	O
of	O
modern	O
optical	O
networks	O
.	O
</s>
<s>
SRLGs	O
typically	O
deal	O
with	O
links	O
between	O
fiber	O
optic	O
nodes	B-Protocol
,	O
but	O
that	O
is	O
not	O
always	O
the	O
case	O
.	O
</s>
<s>
Fiber	O
spans	O
are	O
fiber	O
optic	O
cables	O
that	O
connect	O
two	O
nodes	B-Protocol
.	O
</s>
<s>
In	O
optical	B-Protocol
mesh	I-Protocol
networks	I-Protocol
,	O
nodes	B-Protocol
are	O
junctions	O
of	O
fiber	O
spans	O
.	O
</s>
<s>
Some	O
nodes	B-Protocol
might	O
contain	O
highly	O
sophisticated	O
routing	O
equipment	O
—	O
while	O
others	O
may	O
be	O
just	O
a	O
patch	O
panel	O
.	O
</s>
<s>
Shared	O
risk	O
group	O
also	O
extends	O
within	O
a	O
node	O
itself	O
—	O
in	O
particular	O
nodes	B-Protocol
that	O
contain	O
multi-port	O
network	O
cards	O
.	O
</s>
<s>
Dense	B-Architecture
wavelength	I-Architecture
division	I-Architecture
multiplexing	I-Architecture
equipment	O
are	O
also	O
considered	O
SREG	O
because	O
if	O
a	O
DWDM	O
Mux	O
fails	O
that	O
affects	O
all	O
of	O
the	O
channels	O
through	O
that	O
DWDM	O
.	O
</s>
<s>
When	O
provisioning	O
a	O
circuit	O
,	O
engineers	O
typically	O
use	O
a	O
shortest	O
path	O
algorithm	O
,	O
such	O
as	O
Dijkstra	B-Algorithm
.	O
</s>
<s>
The	O
graph	O
depicts	O
that	O
,	O
between	O
two	O
nodes	B-Protocol
,	O
there	O
exist	O
multiple	O
paths	O
,	O
which	O
may	O
include	O
other	O
nodes	B-Protocol
.	O
</s>
<s>
One	O
of	O
these	O
attempts	O
is	O
by	O
means	O
of	O
a	O
graph	B-Application
transformation	I-Application
approach	O
.	O
</s>
<s>
After	O
obtaining	O
the	O
transformed	O
graph	O
one	O
would	O
simply	O
compute	O
the	O
primary	O
path	O
using	O
a	O
known	O
shortest	O
path	O
algorithm	O
such	O
as	O
Dijkstra	B-Algorithm
's	O
.	O
</s>
<s>
On	O
computing	O
the	O
primary	O
path	O
,	O
and	O
removing	O
all	O
nodes	B-Protocol
and	O
links	O
in	O
that	O
path	O
,	O
run	O
the	O
algorithm	O
again	O
on	O
the	O
remaining	O
network	O
.	O
</s>
<s>
Active	O
components	O
are	O
those	O
that	O
can	O
be	O
monitored	O
,	O
and	O
they	O
include	O
:	O
amplifiers	O
,	O
transponders	B-Architecture
,	O
regenerators	O
,	O
and	O
DWDM	O
Mux/DeMuxs	O
.	O
</s>
