<s>
Path	B-Protocol
protection	I-Protocol
in	O
telecommunications	O
is	O
an	O
end-to-end	O
protection	O
scheme	O
used	O
in	O
connection	B-Protocol
oriented	I-Protocol
circuits	O
in	O
different	O
network	B-Architecture
architectures	I-Architecture
to	O
protect	O
against	O
inevitable	O
failures	O
on	O
service	O
providers’	O
network	O
that	O
might	O
affect	O
the	O
services	O
offered	O
to	O
end	O
customers	O
.	O
</s>
<s>
In	O
ring-based	B-Architecture
networks	I-Architecture
topology	O
where	O
the	O
setup	O
is	O
to	O
form	O
a	O
closed	O
loop	O
among	O
the	O
Add	O
Drop	O
Multiplexers	O
,	O
there	O
is	O
basically	O
one	O
path	O
related	O
ring	B-Architecture
protection	I-Architecture
scheme	O
available	O
in	O
Unidirectional	O
Path-Switched	O
Ring	O
architecture	O
.	O
</s>
<s>
In	O
SDH	B-Protocol
networks	O
,	O
the	O
equivalent	O
of	O
UPSR	O
is	O
Sub-Network	B-Protocol
Connection	I-Protocol
Protection	I-Protocol
(	O
SNCP	O
)	O
.	O
</s>
<s>
Note	O
that	O
SNCP	O
does	O
not	O
assume	O
a	O
ring	B-Architecture
topology	I-Architecture
,	O
and	O
can	O
also	O
be	O
used	O
in	O
mesh	O
topologies	O
.	O
</s>
<s>
Circuits	O
in	O
optical	B-Protocol
mesh	I-Protocol
networks	I-Protocol
can	O
be	O
unprotected	O
,	O
protected	O
to	O
a	O
single	O
failure	O
,	O
and	O
protected	O
to	O
multiple	O
failures	O
.	O
</s>
<s>
The	O
end	O
optical	O
switches	O
in	O
protected	O
circuits	O
are	O
in	O
charge	O
of	O
detecting	O
the	O
failure	O
,	O
in	O
some	O
cases	O
requesting	O
digital	B-Architecture
cross	I-Architecture
connects	I-Architecture
or	O
optical	B-Protocol
cross-connects	I-Protocol
in	O
intermediate	O
devices	O
,	O
and	O
switching	O
the	O
traffic	O
to/from	O
the	O
backup	O
path	O
.	O
</s>
<s>
They	O
can	O
also	O
be	O
node	O
diverse	O
,	O
which	O
offers	O
more	O
protection	O
in	O
case	O
a	O
node	O
failure	O
occurs	O
;	O
depending	O
on	O
the	O
network	O
sometimes	O
the	O
primary	O
and	O
backup	O
path	O
cannot	O
be	O
provisioned	B-Operating_System
to	O
be	O
node	O
diverse	O
at	O
the	O
edges	O
,	O
ingress	O
and	O
egress	O
,	O
node	O
.	O
</s>
<s>
In	O
DBPP	O
,	O
both	O
the	O
primary	O
and	O
backup	O
path	O
carry	O
the	O
traffic	O
end	O
to	O
end	O
,	O
then	O
it	O
is	O
up	O
to	O
the	O
receiver	O
to	O
decide	O
which	O
of	O
the	O
two	O
incoming	O
traffic	O
it	O
is	O
going	O
to	O
pick	O
;	O
this	O
is	O
exactly	O
the	O
same	O
concept	O
as	O
in	O
Ring	O
Based	O
Path	B-Protocol
Protection	I-Protocol
.	O
</s>
<s>
Being	O
the	O
fastest	O
protection	O
scheme	O
also	O
makes	O
it	O
the	O
most	O
expensive	O
;	O
normally	O
using	O
more	O
than	O
double	O
of	O
the	O
provisioned	B-Operating_System
capacity	O
for	O
the	O
primary	O
because	O
the	O
backup	O
path	O
is	O
usually	O
longer	O
due	O
to	O
the	O
link	O
and/or	O
node	O
diversity	O
rule	O
of	O
thumb	O
.	O
</s>
<s>
First	O
,	O
there	O
is	O
the	O
failure	O
dependent	O
assignment	O
or	O
approach	O
also	O
known	O
as	O
restoration	B-Protocol
in	O
which	O
the	O
backup	O
path	O
is	O
calculated	O
in	O
real	O
time	O
after	O
the	O
failure	O
occurs	O
.	O
</s>
<s>
However	O
,	O
in	O
today	O
’s	O
Optical	B-Protocol
Mesh	I-Protocol
Network	I-Protocol
it	O
can	O
be	O
used	O
as	O
a	O
re-provisioning	O
technique	O
to	O
help	O
recover	O
a	O
second	O
failure	O
when	O
the	O
backup	O
resources	O
are	O
already	O
in	O
use	O
.	O
</s>
<s>
The	O
down	O
side	O
to	O
restoration	B-Protocol
as	O
a	O
protection	O
technique	O
is	O
that	O
the	O
recovery	O
time	O
is	O
not	O
fast	O
enough	O
.	O
</s>
<s>
Here	O
the	O
backup	O
path	O
is	O
calculated	O
together	O
with	O
the	O
primary	O
at	O
provisioning	B-Operating_System
time	O
.	O
</s>
<s>
Even	O
though	O
the	O
backup	O
path	O
is	O
calculated	O
,	O
it	O
is	O
not	O
assigned	O
to	O
a	O
specific	O
circuit	O
before	O
a	O
failure	O
occurs	O
;	O
cross	B-Architecture
connect	I-Architecture
requests	O
are	O
initiated	O
after	O
the	O
fact	O
on	O
a	O
first-come	O
,	O
first-served	O
basis	O
.	O
</s>
<s>
Since	O
this	O
approach	O
can	O
only	O
protect	O
from	O
a	O
single	O
failure	O
at	O
a	O
time	O
,	O
if	O
a	O
second	O
primary	O
path	O
fails	O
and	O
at	O
least	O
a	O
portion	O
of	O
its	O
backup	O
path	O
is	O
already	O
in	O
used	O
,	O
this	O
path	O
wo	O
n't	O
be	O
able	O
to	O
recover	O
unless	O
restoration	B-Protocol
technique	O
is	O
in	O
place	O
for	O
such	O
cases	O
.	O
</s>
<s>
Multi-Protocol	B-Protocol
Label	I-Protocol
Switching	I-Protocol
(	O
MPLS	B-Protocol
)	O
architecture	O
is	O
described	O
in	O
the	O
.	O
</s>
<s>
It	O
is	O
a	O
packet-based	B-Protocol
network	I-Protocol
technology	O
that	O
provides	O
a	O
framework	O
for	O
recovery	O
through	O
the	O
creation	O
of	O
point	O
to	O
point	O
paths	O
called	O
Label	O
Switched	O
Paths	O
(	O
LSP	O
)	O
.	O
</s>
<s>
These	O
LSPs	O
creation	O
are	O
between	O
a	O
head-end	O
and	O
a	O
tail-end	O
Label	B-Protocol
Switch	I-Protocol
Router	I-Protocol
(	O
LSR	O
)	O
.	O
</s>
<s>
In	O
the	O
former	O
case	O
,	O
the	O
head-end	O
router	O
is	O
the	O
input	O
or	O
ingress	B-General_Concept
router	I-General_Concept
.	O
</s>
<s>
In	O
the	O
latter	O
case	O
the	O
tail-end	O
represents	O
the	O
output	O
or	O
egress	B-General_Concept
router	I-General_Concept
in	O
the	O
path	O
.	O
</s>
<s>
There	O
are	O
a	O
few	O
protection	O
techniques	O
for	O
MPLS	B-Protocol
very	O
similar	O
in	O
the	O
general	O
concept	O
to	O
those	O
for	O
Optical	B-Protocol
Mesh	I-Protocol
Networks	I-Protocol
,	O
such	O
as	O
link	O
protection	O
(	O
e.g.	O
,	O
MPLS	B-General_Concept
local	I-General_Concept
protection	I-General_Concept
)	O
and	O
path	B-Protocol
protection	I-Protocol
.	O
</s>
<s>
The	O
path	B-Protocol
protection	I-Protocol
schemes	O
for	O
MPLS	B-Protocol
are	O
as	O
follow	O
:	O
</s>
<s>
This	O
protection	O
scheme	O
is	O
similar	O
in	O
a	O
sense	O
to	O
Ring-based	O
path	B-Protocol
protection	I-Protocol
and	O
Dedicated	O
Backup	O
Path	B-Protocol
Protection	I-Protocol
(	O
DBPP	O
)	O
schemes	O
described	O
before	O
.	O
</s>
<s>
As	O
with	O
DBPP	O
in	O
Optical	B-Protocol
Mesh	I-Protocol
Network	I-Protocol
,	O
there	O
is	O
no	O
signaling	O
involved	O
in	O
this	O
protection	O
scheme	O
.	O
</s>
<s>
In	O
this	O
protection	O
scheme	O
,	O
a	O
primary	O
and	O
a	O
backup	O
LSP	O
are	O
computed	O
and	O
setup	O
at	O
the	O
provisioning	B-Operating_System
time	O
prior	O
to	O
failures	O
.	O
</s>
