The Network Control Protocol (NCP) was a

communication protocol A communication protocol is a system of rules that allows two or more entities of a communications system to transmit information via any kind of variation of a physical quantity. The protocol defines the rules, syntax, semantics (computer scien ...

for a

computer network A computer network is a set of computers sharing resources located on or provided by network nodes. The computers use common communication protocols over digital interconnections to communicate with each other. These interconnections are ...

in the 1970s and early 1980s. It provided the middle layers of the

protocol stack The protocol stack or network stack is an implementation of a computer networking protocol suite or protocol family. Some of these terms are used interchangeably but strictly speaking, the ''suite'' is the definition of the communication protoco ...

running on host computers of the

ARPANET The Advanced Research Projects Agency Network (ARPANET) was the first wide-area packet-switched network with distributed control and one of the first networks to implement the TCP/IP protocol suite. Both technologies became the technical fou ...

, the predecessor to the modern

Internet The Internet (or internet) is the global system of interconnected computer networks that uses the Internet protocol suite (TCP/IP) to communicate between networks and devices. It is a '' network of networks'' that consists of private, pub ...

. NCP preceded the

Transmission Control Protocol The Transmission Control Protocol (TCP) is one of the main protocols of the Internet protocol suite. It originated in the initial network implementation in which it complemented the Internet Protocol (IP). Therefore, the entire suite is commonly ...

(TCP) as a

transport layer In computer networking, the transport layer is a conceptual division of methods in the layered architecture of protocols in the network stack in the Internet protocol suite and the OSI model. The protocols of this layer provide end-to-end ...

protocol used during the early ARPANET. NCP was a simplex protocol that utilized two port addresses, establishing two connections, for two-way communications. An odd and an even port were reserved for each

application layer An application layer is an abstraction layer that specifies the shared communications protocols and Interface (computing), interface methods used by Host (network), hosts in a communications network. An ''application layer'' abstraction is speci ...

application or protocol. The standardization of TCP and UDP reduced the need for the use of two simplex ports for each application down to one duplex port. There is some confusion over the name, even among the engineers who worked with the ARPANET. Originally, there was no need for a name for the protocol stack as a whole, so none existed. When the development of TCP started, a name was required for its predecessor, and the pre-existing acronym 'NCP' (which originally referred to Network Control Program, the software which implemented this stack) was organically adopted for that use. Eventually, it was realized that the original expansion of that acronym was inappropriate for its new meaning, so a new quasi-

backronym A backronym is an acronym formed from an already existing word by expanding its letters into the words of a phrase. Backronyms may be invented with either serious or humorous intent, or they may be a type of false etymology or folk etymology. The ...

was created, 'Network Control Protocol' - again, organically, not via a formal decision.

History

NCP was first specified and described in the ARPANETs earliest

RFC RFC may refer to: Computing * Request for Comments, a memorandum on Internet standards * Request for change, change management * Remote Function Call, in SAP computer systems * Rhye's and Fall of Civilization, a modification for Sid Meier's Civ ...

documents in 1969 after a series of meetings on the topic with engineers from

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, and

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. It was finalized in in early 1970, and deployed to all nodes on the ARPANET in December 1970. It remained in use until the end of 1982; see Flag Day below. NCP provided connections and flow control between processes running on different ARPANET host computers. Application services, such as remote login and the

file transfer File transfer is the transmission of a computer file through a communication channel from one computer system to another. Typically, file transfer is mediated by a communications protocol. In the history of computing, numerous file transfer protocol ...

, would be built on top of NCP, using it to handle connections to other host computers. On the ARPANET, the protocols in the

physical layer In the seven-layer OSI model of computer networking, the physical layer or layer 1 is the first and lowest layer; The layer most closely associated with the physical connection between devices. This layer may be implemented by a PHY chip. The ...

, the

data link layer The data link layer, or layer 2, is the second layer of the seven-layer OSI model of computer networking. This layer is the protocol layer that transfers data between nodes on a network segment across the physical layer. The data link layer p ...

, and the

network layer In the seven-layer OSI model of computer networking, the network layer is layer 3. The network layer is responsible for packet forwarding including routing through intermediate routers. Functions The network layer provides the means of transfe ...

used within the network were implemented on separate

Interface Message Processor The Interface Message Processor (IMP) was the packet switching node used to interconnect participant networks to the ARPANET from the late 1960s to 1989. It was the first generation of gateways, which are known today as routers. An IMP was a r ...

s (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 The Interface Message Processor (IMP) was the packet switching node used to interconnect participant networks to the ARPANET from the late 1960s to 1989. It was the first generation of gateways, which are known today as routers. An IMP was a r ...

. Since lower protocol layers were provided by the IMP-host interface, NCP essentially provided a

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 The File Transfer Protocol (FTP) is a standard communication protocol used for the transfer of computer files from a server to a client on a computer network. FTP is built on a client–server model architecture using separate control and data ...

) accessed network services through an interface to the top layer of the NCP, a forerunner to the

Berkeley sockets Berkeley sockets is an application programming interface (API) for Internet sockets and Unix domain sockets, used for inter-process communication (IPC). It is commonly implemented as a library of linkable modules. It originated with the 4.2BSD ...

interface. Stephen D. Crocker, then a graduate student at UCLA, formed and led the Network Working Group (NWG) and specifically led the development of NCP. Other participants in the NWG developed application level protocols such as

TELNET Telnet is an application protocol used on the Internet or local area network to provide a bidirectional interactive text-oriented communication facility using a virtual terminal connection. User data is interspersed in-band with Telnet control i ...

, and, in the 1980s,

SMTP The Simple Mail Transfer Protocol (SMTP) is an Internet standard communication protocol for electronic mail transmission. Mail servers and other message transfer agents use SMTP to send and receive mail messages. User-level email clients typical ...

, among others.

Transition to TCP/IP

On January 1, 1983, in what is known as a '' 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 The Internet protocol suite, commonly known as TCP/IP, is a framework for organizing the set of communication protocols used in the Internet and similar computer networks according to functional criteria. The foundational protocols in the suit ...

protocol suite, marking the start of the modern

History

Transition to TCP/IP

See also

References

Further reading