<s>
Packet	B-Protocol
forwarding	I-Protocol
is	O
the	O
relaying	O
of	O
packets	B-Protocol
from	O
one	O
network	B-Protocol
segment	I-Protocol
to	O
another	O
by	O
nodes	B-Protocol
in	O
a	O
computer	B-Architecture
network	I-Architecture
.	O
</s>
<s>
The	O
network	B-Application
layer	I-Application
in	O
the	O
OSI	O
model	O
is	O
responsible	O
for	O
packet	B-Protocol
forwarding	I-Protocol
.	O
</s>
<s>
The	O
simplest	O
forwarding	O
modelunicastinginvolves	O
a	O
packet	B-Protocol
being	O
relayed	O
from	O
link	O
to	O
link	O
along	O
a	O
chain	O
leading	O
from	O
the	O
packet	B-Protocol
's	O
source	O
to	O
its	O
destination	O
.	O
</s>
<s>
Broadcasting	B-Operating_System
requires	O
a	O
packet	B-Protocol
to	O
be	O
duplicated	O
and	O
copies	O
sent	O
on	O
multiple	O
links	O
with	O
the	O
goal	O
of	O
delivering	O
a	O
copy	O
to	O
every	O
device	O
on	O
the	O
network	O
.	O
</s>
<s>
In	O
practice	O
,	O
broadcast	B-Operating_System
packets	I-Operating_System
are	O
not	O
forwarded	O
everywhere	O
on	O
a	O
network	O
,	O
but	O
only	O
to	O
devices	O
within	O
a	O
broadcast	B-Architecture
domain	I-Architecture
,	O
making	O
broadcast	B-Operating_System
a	O
relative	O
term	O
.	O
</s>
<s>
Less	O
common	O
than	O
broadcasting	B-Operating_System
,	O
but	O
perhaps	O
of	O
greater	O
utility	O
and	O
theoretical	O
significance	O
,	O
is	O
multicasting	O
,	O
where	O
a	O
packet	B-Protocol
is	O
selectively	O
duplicated	O
and	O
copies	O
delivered	O
to	O
each	O
of	O
a	O
set	O
of	O
recipients	O
.	O
</s>
<s>
For	O
example	O
,	O
fiber	O
optics	O
and	O
copper	O
cables	O
run	O
directly	O
from	O
one	O
machine	O
to	O
another	O
to	O
form	O
a	O
natural	O
unicast	B-Protocol
mediadata	O
transmitted	O
at	O
one	O
end	O
is	O
received	O
by	O
only	O
one	O
machine	O
at	O
the	O
other	O
end	O
.	O
</s>
<s>
However	O
,	O
as	O
illustrated	O
in	O
the	O
diagrams	O
,	O
nodes	B-Protocol
can	O
forward	O
packets	B-Protocol
to	O
create	O
multicast	O
or	O
broadcast	B-Operating_System
distributions	O
from	O
naturally	O
unicast	B-Protocol
media	O
.	O
</s>
<s>
Likewise	O
,	O
traditional	O
Ethernet	O
(	O
10BASE5	O
and	O
10BASE2	O
,	O
but	O
not	O
the	O
more	O
modern	O
10BASE-T	B-Protocol
)	O
are	O
natural	O
broadcast	B-Operating_System
mediaall	O
the	O
nodes	B-Protocol
are	O
attached	O
to	O
a	O
single	O
long	O
cable	O
and	O
a	O
packet	B-Protocol
transmitted	O
by	O
one	O
device	O
is	O
seen	O
by	O
every	O
other	O
device	O
attached	O
to	O
the	O
cable	O
.	O
</s>
<s>
Ethernet	O
nodes	B-Protocol
implement	O
unicast	B-Protocol
by	O
ignoring	O
packets	B-Protocol
not	O
directly	O
addressed	O
to	O
them	O
.	O
</s>
<s>
A	O
wireless	B-General_Concept
network	I-General_Concept
is	O
naturally	O
multicast	O
all	O
devices	O
within	O
a	O
reception	O
radius	O
of	O
a	O
transmitter	O
can	O
receive	O
its	O
packets	B-Protocol
.	O
</s>
<s>
Wireless	O
nodes	B-Protocol
ignore	O
packets	B-Protocol
addressed	O
to	O
other	O
devices	O
,	O
but	O
require	O
forwarding	O
to	O
reach	O
nodes	B-Protocol
outside	O
their	O
reception	O
radius	O
.	O
</s>
<s>
At	O
nodes	B-Protocol
where	O
multiple	O
outgoing	O
links	O
are	O
available	O
,	O
the	O
choice	O
of	O
which	O
,	O
all	O
,	O
or	O
any	O
to	O
use	O
for	O
forwarding	O
a	O
given	O
packet	B-Protocol
requires	O
a	O
decision-making	O
process	O
that	O
,	O
while	O
simple	O
in	O
concept	O
,	O
is	O
sometimes	O
bewilderingly	O
complex	O
.	O
</s>
<s>
Since	O
a	O
forwarding	O
decision	O
must	O
be	O
made	O
for	O
every	O
packet	B-Protocol
handled	O
by	O
a	O
node	O
,	O
the	O
total	O
time	O
required	O
for	O
this	O
can	O
become	O
a	O
major	O
limiting	O
factor	O
in	O
overall	O
network	O
performance	O
.	O
</s>
<s>
Much	O
of	O
the	O
design	O
effort	O
of	O
high-speed	O
routers	B-Protocol
and	O
switches	O
has	O
been	O
focused	O
on	O
making	O
rapid	O
forwarding	O
decisions	O
for	O
large	O
numbers	O
of	O
packets	B-Protocol
.	O
</s>
<s>
The	O
forwarding	O
decision	O
is	O
generally	O
made	O
using	O
one	O
of	O
two	O
processes	O
:	O
routing	B-Protocol
,	O
which	O
uses	O
information	O
encoded	O
in	O
a	O
device	O
's	O
address	O
to	O
infer	O
its	O
location	O
on	O
the	O
network	O
,	O
or	O
bridging	B-Protocol
,	O
which	O
makes	O
no	O
assumptions	O
about	O
where	O
addresses	O
are	O
located	O
and	O
depends	O
heavily	O
on	O
broadcasting	B-Operating_System
to	O
locate	O
unknown	O
addresses	O
.	O
</s>
<s>
The	O
heavy	O
overhead	O
of	O
broadcasting	B-Operating_System
has	O
led	O
to	O
the	O
dominance	O
of	O
routing	B-Protocol
in	O
large	O
networks	O
,	O
particularly	O
the	O
Internet	O
;	O
bridging	B-Protocol
is	O
largely	O
relegated	O
to	O
small	O
networks	O
where	O
the	O
overhead	O
of	O
broadcasting	B-Operating_System
is	O
tolerable	O
.	O
</s>
<s>
However	O
,	O
since	O
large	O
networks	O
are	O
usually	O
composed	O
of	O
many	O
smaller	O
networks	O
linked	O
together	O
,	O
it	O
would	O
be	O
inaccurate	O
to	O
state	O
that	O
bridging	B-Protocol
has	O
no	O
use	O
on	O
the	O
Internet	O
;	O
rather	O
,	O
its	O
use	O
is	O
localized	O
.	O
</s>
<s>
A	O
node	O
can	O
use	O
one	O
of	O
two	O
different	O
methods	O
to	O
forward	O
packets	B-Protocol
:	O
store-and-forward	B-Protocol
or	O
cut-through	B-Protocol
switching	I-Protocol
.	O
</s>
