<s>
Ethernet	B-Protocol
Ring	I-Protocol
Protection	I-Protocol
Switching	I-Protocol
,	O
or	O
ERPS	B-Protocol
,	O
is	O
an	O
effort	O
at	O
ITU-T	O
under	O
G.8032	B-Protocol
Recommendation	O
to	O
provide	O
sub-50ms	O
protection	O
and	O
recovery	O
switching	O
for	O
Ethernet	O
traffic	O
in	O
a	O
ring	B-Architecture
topology	I-Architecture
and	O
at	O
the	O
same	O
time	O
ensuring	O
that	O
there	O
are	O
no	O
loops	O
formed	O
at	O
the	O
Ethernet	O
layer	O
.	O
</s>
<s>
This	O
ITU-T	O
specification	O
is	O
directly	O
based	O
on	O
and	O
derived	O
from	O
the	O
Ethernet	B-Protocol
Automatic	I-Protocol
Protection	I-Protocol
Switching	I-Protocol
technology	O
developed	O
and	O
patented	O
by	O
Extreme	O
Networks	O
.	O
</s>
<s>
G.8032v1	O
supported	O
a	O
single	O
ring	B-Architecture
topology	I-Architecture
and	O
G.8032v2	O
supports	O
multiple	O
rings/ladder	O
topology	O
.	O
</s>
<s>
ERPS	B-Protocol
specifies	O
protection	O
switching	O
mechanisms	O
and	O
a	O
protocol	O
for	O
Ethernet	O
layer	O
network	O
(	O
ETH	O
)	O
rings	O
.	O
</s>
<s>
Each	O
Ethernet	O
Ring	O
Node	B-Protocol
is	O
connected	O
to	O
adjacent	O
Ethernet	O
Ring	O
Nodes	O
participating	O
in	O
the	O
same	O
Ethernet	O
Ring	O
,	O
using	O
two	O
independent	O
links	O
.	O
</s>
<s>
One	O
designated	O
Ethernet	O
Ring	O
Node	B-Protocol
,	O
the	O
RPL	O
Owner	O
Node	B-Protocol
,	O
is	O
responsible	O
for	O
blocking	O
traffic	O
at	O
one	O
end	O
of	O
the	O
RPL	O
.	O
</s>
<s>
Under	O
an	O
Ethernet	O
ring	O
failure	O
condition	O
,	O
the	O
RPL	O
Owner	O
Node	B-Protocol
is	O
responsible	O
for	O
unblocking	O
its	O
end	O
of	O
the	O
RPL	O
(	O
unless	O
the	O
RPL	O
has	O
failed	O
)	O
allowing	O
the	O
RPL	O
to	O
be	O
used	O
for	O
traffic	O
.	O
</s>
<s>
Node	B-Protocol
adjacent	O
to	O
the	O
RPL	O
,	O
the	O
RPL	O
Neighbour	O
Node	B-Protocol
,	O
may	O
also	O
participate	O
in	O
blocking	O
or	O
unblocking	O
its	O
end	O
of	O
the	O
RPL	O
.	O
</s>
<s>
Version	O
2	O
of	O
G.8032	B-Protocol
introduced	O
many	O
additional	O
features	O
,	O
such	O
as	O
:	O
</s>
<s>
In	O
ERPS	B-Protocol
there	O
is	O
a	O
central	O
node	B-Protocol
called	O
RPL	O
Owner	O
Node	B-Protocol
which	O
blocks	O
one	O
of	O
the	O
ports	O
to	O
ensure	O
that	O
there	O
is	O
no	O
loop	O
formed	O
for	O
the	O
Ethernet	O
traffic	O
.	O
</s>
<s>
The	O
link	O
blocked	O
by	O
the	O
RPL	O
owner	O
node	B-Protocol
is	O
called	O
the	O
Ring	O
Protection	O
Link	O
or	O
RPL	O
.	O
</s>
<s>
The	O
node	B-Protocol
at	O
the	O
other	O
end	O
of	O
the	O
RPL	O
is	O
known	O
as	O
RPL	O
Neighbor	O
Node	B-Protocol
.	O
</s>
<s>
Any	O
failure	O
along	O
the	O
ring	O
triggers	O
a	O
R-APS(SF )	O
(	O
R-APS	O
signal	O
fail	O
)	O
message	B-Protocol
along	O
both	O
directions	O
from	O
the	O
nodes	O
adjacent	O
to	O
the	O
failed	O
link	O
after	O
these	O
nodes	O
have	O
blocked	O
the	O
port	O
facing	O
the	O
failed	O
link	O
.	O
</s>
<s>
On	O
obtaining	O
this	O
message	B-Protocol
,	O
RPL	O
owner	O
unblocks	O
the	O
RPL	O
port	O
.	O
</s>
<s>
On	O
obtaining	O
this	O
message	B-Protocol
,	O
the	O
RPL	O
owner	O
block	O
the	O
RPL	O
port	O
and	O
then	O
sends	O
a	O
R-APS(NR,RB )	O
(	O
R-APS	O
no	O
request	O
,	O
RPL	O
blocked	O
)	O
message	B-Protocol
.	O
</s>
<s>
This	O
protocol	O
is	O
robust	O
enough	O
to	O
work	O
for	O
unidirectional	O
failure	O
and	O
multiple	O
link	O
failure	O
scenarios	O
in	O
a	O
ring	B-Architecture
topology	I-Architecture
.	O
</s>
