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{{About|the IBM Network Control Program software|the [[ARPANET]] Network Control Program|Network Control Program (ARPANET)}}

The '''IBM Network Control Program''', or '''NCP''', was software that ran on a [[IBM 37xx|37xx]] communications controller and managed communication with remote devices. NCP provided services comparable to the [[data link layer]] and [[Network Layer]] functions in the [[OSI model]] of a [[Wide area network]].<ref>{{cite web|last=Microsoft|title=SNA Functional Layers|url=https://technet.microsoft.com/en-us/library/cc977037.aspx|accessdate=Sep 7, 2012}}</ref>

==Overview==
The original [[IBM]] Network Control Program ran on the [[IBM 3705|3705-I]] and supported access to older devices by application programs using [[Telecommunications Access Method|Telecommunications Access Method (TCAM)]]. With the advent of [[Systems Network Architecture]] (SNA), NCP was enhanced to connect cluster controllers (such as the [[IBM 3270#Controllers|IBM 3270]]) to application programs using TCAM and later to application programs using [[Virtual Telecommunications Access Method|Virtual Telecommunications Access Method (VTAM)]]. Subsequent versions of NCP were released to run on the IBM 3704, [[IBM 3705|IBM 3705-II]], IBM 3725. IBM 3720, or [[IBM 3745]] Communications Controllers, all of which SNA defined as a [[Systems Network Architecture#Physical_Unit_(PU)|SNA Physical Unit Type 4]] (PU4). A PU4 usually had [[Synchronous Data Link Control|SDLC]] links to remote cluster controllers (PU1/PU2) or to other PU4s. Polling and addressing of the cluster controllers was performed by the NCP without mainframe intervention.

In 2005 IBM introduced [[Communications Controller for Linux]] (CCL), a software product that allows an unmodified NCP to run on the mainframe, eliminating the need for a separate communications controller in some cases.

A ''local'' NCP connected to a [[System/370]] [[I/O channel|channel]] via single<ref group=NB>However, if NCP was generated with '''Partitioned Emulation Program (PEP)''', then the '''Emulator Program (EP)''' has its own block of I/O addresses, normally on a different channel from that used by the NCP proper. The EP part of a PEP was often used to communicate with the Message Control Program (MCP) provided by TCAM running in the mainframe as the interface with application programs.</ref> address.

A ''remote'' NCP had no direct connection to a mainframe but was connected to a local NCP via one or more high-speed SDLC links.

==Notes==
{{Reflist|group=NB}}

==References==
{{Reflist}}

==Further reading==

*{{cite web | author=W. S. Hobgood | title=The role of the Network Control Program in Systems Network Architecture | publisher=IBM Systems Journal | year=1976 | version=Vol 15, No 1 | url=http://www.research.ibm.com/journal/sj/151/ibmsj1501E.pdf | accessdate=2006-08-26 | url-status=bot: unknown | archiveurl=https://web.archive.org/web/20070316233256/http://www.research.ibm.com/journal/sj/151/ibmsj1501E.pdf | archivedate=2007-03-16 }}

[[Category:Systems Network Architecture|Network Control Program]]
[[Category:Network protocols]]
[[Category:IBM software|Network Control Program]]

IBM Network Control Program - Revision history

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