<s>
Pipeline	B-Protocol
forwarding	I-Protocol
(	O
PF	O
)	O
applies	O
to	O
packet	B-Protocol
forwarding	I-Protocol
in	O
computer	B-Architecture
networks	I-Architecture
the	O
basic	O
concept	O
of	O
pipelining	B-General_Concept
,	O
which	O
has	O
been	O
widely	O
and	O
successfully	O
used	O
in	O
computing	O
—	O
specifically	O
,	O
in	O
the	O
architecture	O
of	O
all	O
major	O
central	B-General_Concept
processing	I-General_Concept
units	I-General_Concept
(	O
CPUs	O
)	O
—	O
and	O
manufacturing	O
—	O
specifically	O
in	O
assembly	O
lines	O
of	O
various	O
industries	O
starting	O
from	O
automotive	O
to	O
many	O
others	O
.	O
</s>
<s>
Pipelining	B-General_Concept
is	O
known	O
to	O
be	O
optimal	O
independent	O
of	O
the	O
specific	O
instantiation	O
.	O
</s>
<s>
As	O
in	O
other	O
pipelining	B-General_Concept
implementations	O
,	O
a	O
common	O
time	O
reference	O
(	O
CTR	O
)	O
is	O
needed	O
to	O
perform	O
pipeline	B-Protocol
forwarding	I-Protocol
.	O
</s>
<s>
Alternatively	O
,	O
or	O
complementary	O
,	O
the	O
CTR	O
can	O
be	O
obtained	O
through	O
the	O
network	O
by	O
means	O
of	O
synchronization	O
protocols	O
such	O
as	O
IEEE	B-Protocol
1588	I-Protocol
.	O
</s>
<s>
The	O
periodic	O
scheduling	O
within	O
each	O
node	O
results	O
in	O
a	O
periodic	O
packet	B-Protocol
forwarding	I-Protocol
across	O
the	O
network	O
,	O
which	O
is	O
referred	O
to	O
as	O
pipeline	B-Protocol
forwarding	I-Protocol
for	O
the	O
ordered	O
,	O
step-by-step	O
fashion	O
with	O
which	O
packets	O
travel	O
toward	O
their	O
destination	O
.	O
</s>
<s>
Through	O
a	O
resource	O
reservation	O
procedure	O
transmission	O
capacity	O
is	O
booked	O
for	O
a	O
flow	O
on	O
each	O
link	O
it	O
traverses	O
during	O
the	O
time	O
frame	O
(	O
or	O
time	O
frames	O
)	O
predefined	O
for	O
its	O
forwarding	O
,	O
thus	O
setting	O
up	O
a	O
synchronous	B-Protocol
virtual	I-Protocol
pipe	I-Protocol
(	O
SVP	B-Protocol
)	O
.	O
</s>
<s>
As	O
exemplified	O
in	O
the	O
figure	O
above	O
,	O
which	O
depicts	O
the	O
journey	O
of	O
a	O
packet	O
from	O
node	O
A	O
to	O
node	O
D	O
along	O
three	O
pipeline	B-Protocol
forwarding	I-Protocol
switches	O
,	O
the	O
forwarding	O
delay	O
may	O
have	O
different	O
values	O
for	O
different	O
nodes	O
,	O
due	O
to	O
different	O
propagation	O
delays	O
on	O
different	O
links	O
(	O
e.g.	O
,	O
Tab	O
,	O
Tbc	O
,	O
and	O
Tcd	O
)	O
,	O
and	O
different	O
packet	O
processing	O
and	O
switching	O
times	O
in	O
heterogeneous	O
nodes	O
(	O
e.g.	O
,	O
Tbb	O
and	O
Tcc	O
)	O
.	O
</s>
<s>
Moreover	O
,	O
two	O
variants	O
of	O
the	O
basic	O
pipeline	B-Protocol
forwarding	I-Protocol
operation	O
are	O
possible	O
.	O
</s>
<s>
Two	O
implementations	O
of	O
the	O
pipeline	B-Protocol
forwarding	I-Protocol
were	O
proposed	O
:	O
Time-Driven	B-Protocol
Switching	I-Protocol
(	O
TDS	B-Protocol
)	O
-	O
a.k.a.	O
</s>
