<s>
The	O
Network	B-Protocol
Control	I-Protocol
Protocol	I-Protocol
(	O
NCP	O
)	O
was	O
a	O
communication	O
protocol	O
for	O
a	O
computer	B-Architecture
network	I-Architecture
in	O
the	O
1970s	O
and	O
early	O
1980s	O
.	O
</s>
<s>
It	O
provided	O
the	O
transport	B-Architecture
layer	I-Architecture
of	O
the	O
protocol	B-Protocol
stack	I-Protocol
running	O
on	O
host	O
computers	O
of	O
the	O
ARPANET	O
,	O
the	O
predecessor	O
to	O
the	O
modern	O
Internet	O
.	O
</s>
<s>
NCP	O
preceded	O
the	O
Transmission	B-Protocol
Control	I-Protocol
Protocol	I-Protocol
(	O
TCP	O
)	O
as	O
a	O
transport	B-Architecture
layer	I-Architecture
protocol	O
used	O
during	O
the	O
early	O
ARPANET	O
.	O
</s>
<s>
NCP	O
was	O
a	O
simplex	O
protocol	O
that	O
utilized	O
two	O
port	B-Protocol
numbers	I-Protocol
,	O
establishing	O
two	O
connections	O
,	O
for	O
two-way	O
communications	O
.	O
</s>
<s>
An	O
odd	O
and	O
an	O
even	O
port	O
were	O
reserved	O
for	O
each	O
application	B-Application
layer	I-Application
application	O
or	O
protocol	O
.	O
</s>
<s>
Originally	O
,	O
there	O
was	O
no	O
need	O
for	O
a	O
name	O
for	O
the	O
protocol	B-Protocol
stack	I-Protocol
as	O
a	O
whole	O
,	O
so	O
none	O
existed	O
.	O
</s>
<s>
When	O
the	O
development	O
of	O
TCP	O
started	O
,	O
a	O
name	O
was	O
required	O
for	O
its	O
predecessor	O
,	O
and	O
the	O
pre-existing	O
acronym	O
'	O
NCP	O
 '	O
(	O
which	O
originally	O
referred	O
to	O
Network	B-Protocol
Control	I-Protocol
Program	I-Protocol
,	O
the	O
software	O
which	O
implemented	O
this	O
stack	O
)	O
was	O
organically	O
adopted	O
for	O
that	O
use	O
.	O
</s>
<s>
Eventually	O
,	O
it	O
was	O
realized	O
that	O
the	O
original	O
expansion	O
of	O
that	O
acronym	O
was	O
inappropriate	O
for	O
its	O
new	O
meaning	O
,	O
so	O
a	O
new	O
quasi-backronym	O
was	O
created	O
,	O
'	O
Network	B-Protocol
Control	I-Protocol
Protocol	I-Protocol
 '	O
-	O
again	O
,	O
organically	O
,	O
not	O
via	O
a	O
formal	O
decision	O
.	O
</s>
<s>
It	O
remained	O
in	O
use	O
until	O
the	O
end	O
of	O
1982	O
;	O
see	O
Flag	B-General_Concept
Day	I-General_Concept
below	O
.	O
</s>
<s>
Application	B-Application
services	I-Application
,	O
such	O
as	O
remote	B-Protocol
login	I-Protocol
and	O
the	O
file	B-Protocol
transfer	I-Protocol
,	O
would	O
be	O
built	O
on	O
top	O
of	O
NCP	O
,	O
using	O
it	O
to	O
handle	O
connections	O
to	O
other	O
host	O
computers	O
.	O
</s>
<s>
On	O
the	O
ARPANET	O
,	O
the	O
protocols	O
in	O
the	O
physical	B-Application
layer	I-Application
,	O
the	O
data	B-Protocol
link	I-Protocol
layer	I-Protocol
,	O
and	O
the	O
network	B-Application
layer	I-Application
used	O
within	O
the	O
network	O
were	O
implemented	O
on	O
separate	O
Interface	B-Protocol
Message	I-Protocol
Processors	I-Protocol
(	O
IMPs	O
)	O
.	O
</s>
<s>
The	O
host	O
usually	O
connected	O
to	O
an	O
IMP	O
using	O
another	O
kind	O
of	O
interface	O
,	O
with	O
different	O
physical	O
,	O
data	O
link	O
and	O
network	B-Application
layer	I-Application
specifications	O
.	O
</s>
<s>
The	O
IMP	O
's	O
capabilities	O
were	O
specified	O
by	O
the	O
Host/IMP	O
Protocol	O
in	O
BBN	B-Protocol
Report	I-Protocol
1822	I-Protocol
.	O
</s>
<s>
Since	O
lower	O
protocol	O
layers	O
were	O
provided	O
by	O
the	O
IMP-host	O
interface	O
,	O
NCP	O
essentially	O
provided	O
a	O
transport	B-Architecture
layer	I-Architecture
consisting	O
of	O
the	O
ARPANET	O
Host-to-Host	O
Protocol	O
(	O
AHHP	O
)	O
and	O
the	O
Initial	O
Connection	O
Protocol	O
(	O
ICP	O
)	O
.	O
</s>
<s>
Application	B-Application
protocols	I-Application
(	O
e.g.	O
,	O
FTP	B-Protocol
)	O
accessed	O
network	O
services	O
through	O
an	O
interface	O
to	O
the	O
top	O
layer	O
of	O
the	O
NCP	O
,	O
a	O
forerunner	O
to	O
the	O
Berkeley	B-Protocol
sockets	I-Protocol
interface	O
.	O
</s>
<s>
Other	O
participants	O
in	O
the	O
NWG	O
developed	O
application	O
level	O
protocols	O
such	O
as	O
TELNET	B-Protocol
,	O
FTP	B-Protocol
,	O
and	O
,	O
in	O
the	O
1980s	O
,	O
SMTP	B-Protocol
,	O
among	O
others	O
.	O
</s>
<s>
On	O
January	O
1	O
,	O
1983	O
,	O
in	O
what	O
is	O
known	O
as	O
a	O
flag	B-General_Concept
day	I-General_Concept
,	O
NCP	O
was	O
officially	O
rendered	O
obsolete	O
when	O
the	O
ARPANET	O
changed	O
its	O
core	O
networking	O
protocols	O
from	O
NCP	O
to	O
the	O
more	O
flexible	O
and	O
powerful	O
TCP/IP	B-Protocol
protocol	I-Protocol
suite	I-Protocol
,	O
marking	O
the	O
start	O
of	O
the	O
modern	O
Internet	O
.	O
</s>
