<s>
The	O
IBM	B-Protocol
Network	I-Protocol
Control	I-Protocol
Program	I-Protocol
,	O
or	O
NCP	O
,	O
was	O
software	O
that	O
ran	O
on	O
a	O
37xx	B-Device
communications	O
controller	O
and	O
managed	O
communication	O
with	O
remote	O
devices	O
.	O
</s>
<s>
NCP	O
provided	O
services	O
comparable	O
to	O
the	O
data	B-Protocol
link	I-Protocol
layer	I-Protocol
and	O
Network	B-Application
Layer	I-Application
functions	O
in	O
the	O
OSI	O
model	O
of	O
a	O
Wide	O
area	O
network	O
.	O
</s>
<s>
The	O
original	O
IBM	B-Protocol
Network	I-Protocol
Control	I-Protocol
Program	I-Protocol
ran	O
on	O
the	O
3705-I	B-Device
and	O
supported	O
access	O
to	O
older	O
devices	O
by	O
application	O
programs	O
using	O
Telecommunications	B-Application
Access	I-Application
Method	I-Application
(	O
TCAM	O
)	O
.	O
</s>
<s>
With	O
the	O
advent	O
of	O
Systems	B-Architecture
Network	I-Architecture
Architecture	I-Architecture
(	O
SNA	O
)	O
,	O
NCP	O
was	O
enhanced	O
to	O
connect	O
cluster	O
controllers	O
(	O
such	O
as	O
the	O
IBM	O
3270	O
)	O
to	O
application	O
programs	O
using	O
TCAM	O
and	O
later	O
to	O
application	O
programs	O
using	O
Virtual	B-Application
Telecommunications	I-Application
Access	I-Application
Method	I-Application
(	O
VTAM	B-Application
)	O
.	O
</s>
<s>
Subsequent	O
versions	O
of	O
NCP	O
were	O
released	O
to	O
run	O
on	O
the	O
IBM	B-Device
3704	I-Device
,	O
IBM	B-Device
3705-II	I-Device
,	O
IBM	O
3725	O
.	O
</s>
<s>
IBM	O
3720	O
,	O
or	O
IBM	B-Device
3745	I-Device
Communications	O
Controllers	O
,	O
all	O
of	O
which	O
SNA	O
defined	O
as	O
a	O
SNA	O
Physical	O
Unit	O
Type	O
4	O
(	O
PU4	O
)	O
.	O
</s>
<s>
A	O
PU4	O
usually	O
had	O
SDLC	B-Protocol
links	O
to	O
remote	O
cluster	O
controllers	O
(	O
PU1/PU2	O
)	O
or	O
to	O
other	O
PU4s	O
.	O
</s>
<s>
In	O
2005	O
IBM	O
introduced	O
Communications	B-Application
Controller	I-Application
for	I-Application
Linux	I-Application
(	O
CCL	O
)	O
,	O
a	O
software	O
product	O
that	O
allows	O
an	O
unmodified	O
NCP	O
to	O
run	O
on	O
the	O
mainframe	O
,	O
eliminating	O
the	O
need	O
for	O
a	O
separate	O
communications	O
controller	O
in	O
some	O
cases	O
.	O
</s>
<s>
A	O
local	O
NCP	O
connected	O
to	O
a	O
System/370	B-Device
channel	B-Device
via	O
single	O
address	O
.	O
</s>
<s>
A	O
remote	O
NCP	O
had	O
no	O
direct	O
connection	O
to	O
a	O
mainframe	O
but	O
was	O
connected	O
to	O
a	O
local	O
NCP	O
via	O
one	O
or	O
more	O
high-speed	O
SDLC	B-Protocol
links	O
.	O
</s>
