<s>
Parallel	B-Protocol
Redundancy	I-Protocol
Protocol	I-Protocol
(	O
PRP	O
)	O
is	O
a	O
network	O
protocol	O
standard	O
for	O
Ethernet	O
that	O
provides	O
seamless	O
failover	B-General_Concept
against	O
failure	O
of	O
any	O
network	O
component	O
.	O
</s>
<s>
This	O
is	O
in	O
contrast	O
to	O
the	O
companion	O
standard	O
HSR	B-Protocol
(	O
IEC	O
62439-3	O
Clause	O
5	O
)	O
,	O
with	O
which	O
PRP	O
shares	O
the	O
operating	O
principle	O
.	O
</s>
<s>
PRP	O
and	O
HSR	B-Protocol
are	O
independent	O
of	O
the	O
application-protocol	O
and	O
can	O
be	O
used	O
by	O
most	O
Industrial	B-Protocol
Ethernet	I-Protocol
protocols	O
in	O
the	O
IEC	O
61784	O
suite	O
.	O
</s>
<s>
PRP	O
and	O
HSR	B-Protocol
are	O
standardized	O
by	O
the	O
IEC	O
62439-3:2016	O
)	O
.	O
</s>
<s>
PRP	O
and	O
HSR	B-Protocol
are	O
suited	O
for	O
applications	O
that	O
request	O
high	O
availability	O
and	O
short	O
switchover	O
time	O
,	O
such	O
as	O
:	O
protection	O
for	O
electrical	O
substation	O
,	O
synchronized	O
drives	O
,	O
for	O
instance	O
in	O
printing	O
machines	O
or	O
high	O
power	O
inverters	O
.	O
</s>
<s>
Each	O
PRP	O
network	B-Protocol
node	I-Protocol
(	O
DANP	O
)	O
has	O
two	O
Ethernet	O
ports	O
attached	O
to	O
two	O
separate	O
local	B-General_Concept
area	I-General_Concept
networks	I-General_Concept
of	O
arbitrary	O
,	O
but	O
similar	O
topology	O
.	O
</s>
<s>
The	O
two	O
LANs	B-General_Concept
have	O
no	O
links	O
connecting	O
them	O
and	O
are	O
assumed	O
to	O
be	O
fail-independent	O
,	O
to	O
avoid	O
common	O
mode	O
failures	O
.	O
</s>
<s>
Since	O
HSR	B-Protocol
and	O
PRP	O
use	O
the	O
same	O
duplicate	O
identification	O
mechanism	O
,	O
PRP	O
and	O
HSR	B-Protocol
networks	O
can	O
be	O
connected	O
without	O
single	O
point	O
of	O
failure	O
and	O
the	O
same	O
nodes	O
can	O
be	O
built	O
to	O
be	O
used	O
in	O
both	O
PRP	O
and	O
HSR	B-Protocol
networks	O
.	O
</s>
<s>
The	O
two	O
frames	O
travel	O
through	O
their	O
respective	O
LANs	B-General_Concept
until	O
they	O
reach	O
a	O
destination	O
node	O
(	O
DANP	O
)	O
with	O
a	O
certain	O
time	O
skew	O
.	O
</s>
<s>
Therefore	O
,	O
as	O
long	O
as	O
one	O
LAN	B-General_Concept
is	O
operational	O
,	O
the	O
destination	O
application	O
always	O
receives	O
one	O
frame	O
.	O
</s>
<s>
This	O
is	O
allowed	O
since	O
the	O
two	O
LANs	B-General_Concept
have	O
no	O
connection	O
.	O
</s>
<s>
A	O
PRP	O
node	O
needs	O
only	O
one	O
IP	B-Protocol
address	O
.	O
</s>
<s>
Especially	O
,	O
the	O
ARP	O
protocol	O
will	O
correctly	O
relate	O
the	O
MAC	O
to	O
the	O
IP	B-Protocol
address	O
.	O
</s>
<s>
IEC	O
62439-3	O
Annex	O
C	O
specifies	O
the	O
Precision	B-Protocol
Time	I-Protocol
Protocol	I-Protocol
Industry	I-Protocol
Profile	I-Protocol
that	O
support	O
a	O
clock	O
synchronization	O
over	O
PRP	O
with	O
an	O
accuracy	O
of	O
1	O
μs	O
after	O
15	O
network	O
elements	O
,	O
as	O
profile	O
of	O
IEEE	O
Std	O
1588	O
Precision	B-Protocol
Time	I-Protocol
Protocol	I-Protocol
.	O
</s>
<s>
This	O
gave	O
a	O
good	O
error	O
detection	O
coverage	O
but	O
made	O
difficult	O
the	O
transition	O
from	O
PRP	O
to	O
the	O
High-availability	B-Protocol
Seamless	I-Protocol
Redundancy	I-Protocol
(	O
HSR	B-Protocol
)	O
protocol	O
,	O
which	O
uses	O
a	O
ring	O
topology	O
instead	O
of	O
parallel	O
networks	O
.	O
</s>
<s>
The	O
revised	O
standard	O
IEC	O
62439-3:2012	O
aligned	O
PRP	O
with	O
HSR	B-Protocol
using	O
the	O
same	O
duplicate	O
discard	O
algorithm	O
.	O
</s>
<s>
This	O
allowed	O
building	O
transparent	O
PRP-HSR	O
connection	O
bridges	O
and	O
nodes	O
that	O
can	O
operate	O
both	O
as	O
PRP	O
(	O
DANP	O
)	O
and	O
HSR	B-Protocol
(	O
DANH	O
)	O
.	O
</s>
