Network Control Program

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This article is about the ARPANET Network Control Program. For the IBM Network Control Program software, see IBM Network Control Program.

The ARPANET Network Control Program (NCP) provided the shared elements of the protocol stack running on an ARPANET host computer. NCP provided connections and flow control between processes running on different ARPANET host computers. Application services, like e-mail or file transfer, used an interface to the NCP to handle connections to other host computers.

On the ARPANET, the physical layer, the data link layer, and the network layer protocols were implemented on separate Interface Message Processors, called IMPs. The bottom of a host's protocol stack connected to the IMP's reliable packet delivery system with numeric host addresses. The IMP's capabilities were specified by the Host/IMP Protocol in BBN Report 1822.

The NCP represented the shared layers of the protocol stack resident on the host computer. Since lower protocol layers were provided by the IMP, NCP essentially provided a transport layer consisting of the ARPANET Host-to-Host Protocol (AHHP) and the Initial Connection Protocol (ICP). The 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, SMTP, etc.) accessed network services through an interface to the top layer of the NCP, a forerunner to the Berkeley sockets interface.

On January 1, 1983, NCP was 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 Internet as we know it today.

[edit] Further reading

  • S. Crocker (16 March 1970). "Protocol Notes". RFC 36. Network Working Group (now IETF). Retrieved on 2006-05-21.
  • 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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