<s>
The	O
Parallel	B-Protocol
Line	I-Protocol
Internet	I-Protocol
Protocol	I-Protocol
(	O
PLIP	B-Protocol
)	O
is	O
a	O
computer	B-Architecture
networking	I-Architecture
protocol	O
for	O
direct	O
computer-to-computer	O
communications	O
using	O
the	O
parallel	B-Device
port	I-Device
normally	O
used	O
for	O
connections	O
to	O
a	O
printer	O
.	O
</s>
<s>
The	O
Parallel	B-Protocol
Line	I-Protocol
Internet	I-Protocol
Protocol	I-Protocol
provides	O
link	B-Protocol
layer	I-Protocol
services	O
for	O
the	O
Internet	B-Protocol
Protocol	I-Protocol
,	O
the	O
protocol	O
used	O
for	O
forming	O
small	O
local	B-General_Concept
area	I-General_Concept
networks	I-General_Concept
and	O
large	O
computer	B-Architecture
networks	I-Architecture
,	O
such	O
as	O
the	O
Internet	O
,	O
enabling	O
computers	O
without	O
standard	O
dedicated	O
networking	O
hardware	O
,	O
such	O
as	O
Ethernet	O
,	O
but	O
with	O
older	O
parallel	B-Device
port	I-Device
devices	O
,	O
to	O
communicate	O
.	O
</s>
<s>
The	O
Internet	B-Protocol
Protocol	I-Protocol
Suite	I-Protocol
is	O
the	O
standards-based	O
networking	O
model	O
and	O
software	O
specification	O
for	O
forming	O
small	O
and	O
large	O
computer	B-Architecture
networks	I-Architecture
,	O
from	O
local	B-General_Concept
area	I-General_Concept
networks	I-General_Concept
to	O
global	O
communication	O
systems	O
,	O
such	O
as	O
the	O
Internet	O
.	O
</s>
<s>
Early	O
personal	B-Device
computers	I-Device
did	O
not	O
have	O
Ethernet	O
hardware	O
included	O
in	O
their	O
design	O
and	O
bus	O
adapters	O
were	O
initially	O
expensive	O
.	O
</s>
<s>
A	O
solution	O
to	O
was	O
to	O
use	O
the	O
,	O
at	O
the	O
time	O
,	O
standard	O
parallel	B-Device
port	I-Device
,	O
typically	O
used	O
for	O
connection	O
to	O
a	O
printer	O
or	O
similar	O
output	O
device	O
.	O
</s>
<s>
The	O
ports	O
on	O
two	O
computers	O
are	O
connected	O
with	O
a	O
so-called	O
null-printer	B-Protocol
cable	I-Protocol
,	O
sometimes	O
called	O
a	O
LapLink	B-Protocol
cable	I-Protocol
.	O
</s>
<s>
The	O
laplink	B-Protocol
cable	I-Protocol
connects	O
five	O
output	O
pins	O
of	O
a	O
parallel	B-Device
port	I-Device
to	O
five	O
input	O
pins	O
on	O
the	O
opposing	O
port	O
,	O
for	O
each	O
direction	O
.	O
</s>
<s>
Due	O
to	O
the	O
lack	O
of	O
an	O
internal	O
timing	O
in	O
the	O
parallel	B-Device
ports	I-Device
,	O
synchronization	O
is	O
implemented	O
via	O
software	O
handshaking	O
:	O
four	O
of	O
the	O
five	O
pins	O
are	O
used	O
for	O
data	O
transfer	O
and	O
one	O
is	O
used	O
for	O
synchronization	O
.	O
</s>
<s>
Transmission	O
of	O
a	O
byte	B-Application
is	O
accomplished	O
by	O
dividing	O
it	O
into	O
two	O
nibbles	O
of	O
four	O
bits	O
each	O
.	O
</s>
<s>
Internet	B-Protocol
Protocol	I-Protocol
packets	O
are	O
sent	O
over	O
the	O
line	O
after	O
encapsulating	O
them	O
into	O
PLIP	B-Protocol
packets	O
before	O
transmission	O
over	O
the	O
line	O
.	O
</s>
<s>
The	O
length	O
and	O
checksum	O
are	O
calculated	O
over	O
the	O
second	O
and	O
third	O
field	O
only	O
,	O
so	O
that	O
the	O
actual	O
total	O
length	O
of	O
the	O
packet	O
is	O
three	O
more	O
than	O
the	O
length	O
as	O
reported	O
in	O
the	O
first	O
two	O
bytes	B-Application
of	O
the	O
packet	O
.	O
</s>
<s>
An	O
analogous	O
feature	O
for	O
serial	O
communications	O
ports	O
is	O
the	O
Serial	B-Protocol
Line	I-Protocol
Internet	I-Protocol
Protocol	I-Protocol
(	O
SLIP	O
)	O
,	O
using	O
null-modem	O
cables	O
,	O
but	O
allows	O
transfer	O
of	O
four	O
bits	O
at	O
a	O
time	O
rather	O
than	O
one	O
.	O
</s>
<s>
Ethernet	O
may	O
also	O
be	O
used	O
as	O
a	O
direct	O
computer-to-computer	O
communications	O
method	O
using	O
an	O
Ethernet	B-Protocol
crossover	I-Protocol
cable	I-Protocol
.	O
</s>
<s>
Other	O
point-to-point	B-Architecture
connections	O
,	O
such	O
as	O
USB	B-Protocol
host-to-host	O
bridges	O
or	O
cables	O
are	O
also	O
used	O
to	O
transfer	O
files	O
between	O
two	O
computers	O
where	O
a	O
network	O
is	O
not	O
necessary	O
or	O
available	O
.	O
</s>
