Network Control Program

Network Control Program
This article is about the ARPANET Network Control Program. For Novell NetWare protocol, see NetWare Core Protocol. For the IBM Network Control Program software, see IBM Network Control Program.

The Network Control Program (NCP) provided the middle layers of the protocol stack running on host computers of the ARPANET, the predecessor to the modern Internet. Although sometimes the abbreviation NCP is mistakenly expanded to Network Control Protocol, this term is not found in the contemporaneous documentation.

Contents

History

NCP provided connections and flow control between processes running on different ARPANET host computers. Application services, such as email and file transfer, were built on top of NCP, using it to handle connections to other host computers.

On the ARPANET, the protocols in the Physical Layer, the Data Link Layer, and the Network Layer used within the network were implemented on separate Interface Message Processors (IMPs). The host usually connected to an IMP using another kind of interface, with different physical, data link and network layer specifications. The IMP's capabilities were specified by the Host/IMP Protocol in BBN Report 1822.

Since lower protocol layers were provided by the IMP-host interface, NCP essentially provided a Transport Layer consisting of the ARPANET Host-to-Host Protocol (AHHP) and the Initial Connection Protocol (ICP). AHHP defined procedures to transmit a unidirectional, flow-controlled data stream between two hosts. The ICP defined the procedure for establishing a bidirectional pair of such streams between a pair of host processes. Application protocols (e.g., FTP) accessed network services through an interface to the top layer of the NCP, a forerunner to the Berkeley sockets interface.

Transition to TCP/IP

On January 1, 1983, known as flag day, NCP was officially rendered obsolete when the ARPANET changed its core networking protocols from NCP to the more flexible and powerful TCP/IP protocol suite, marking the start of the modern Internet.[1]

Notes

  1. ^ Postel, J. (November 1981). "The General Plan". NCP/TCP transition plan. IETF. p. 2. RFC 801. http://tools.ietf.org/html/rfc801#page-2. Retrieved February 1, 2011. 

Further reading

  • S. Crocker (16 March 1970). Protocol Notes. RFC 36. Network Working Group (now IETF). 
  • Postel, Jon; Feinler, E. (1978). ARPANET Protocol Handbook. Menlo Park, CA: Network Information Center. 
  • BBN (May 1978). Interface Message Processor -- Specifications for the Interconnection of a Host and an IMP. BBN Report 1822. Bolt, Beranek, and Newman, Inc.. 

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