Network Control Program
Encyclopedia
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.
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.
, 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.
Protocol stack
The protocol stack is an implementation of a computer networking protocol suite. The terms are often used interchangeably. Strictly speaking, the suite is the definition of the protocols, and the stack is the software implementation of them....
running on host computers of the ARPANET
ARPANET
The Advanced Research Projects Agency Network , was the world's first operational packet switching network and the core network of a set that came to compose the global Internet...
, the predecessor to the modern Internet
Internet
The Internet is a global system of interconnected computer networks that use the standard Internet protocol suite to serve billions of users worldwide...
. Although sometimes the abbreviation NCP is mistakenly expanded to Network Control Protocol, this term is not found in the contemporaneous documentation.
History
NCP provided connections and flow control between processes running on different ARPANET host computers. Application services, such as emailEmail
Electronic mail, commonly known as email or e-mail, is a method of exchanging digital messages from an author to one or more recipients. Modern email operates across the Internet or other computer networks. Some early email systems required that the author and the recipient both be online at the...
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
Physical layer
The physical layer or layer 1 is the first and lowest layer in the seven-layer OSI model of computer networking. The implementation of this layer is often termed PHY....
, the Data Link Layer
Data link layer
The data link layer is layer 2 of the seven-layer OSI model of computer networking. It corresponds to, or is part of the link layer of the TCP/IP reference model....
, and the Network Layer
Network Layer
The network layer is layer 3 of the seven-layer OSI model of computer networking.The network layer is responsible for packet forwarding including routing through intermediate routers, whereas the data link layer is responsible for media access control, flow control and error checking.The network...
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
BBN Report 1822
BBN Report 1822 specifies the method for connecting a host computer to an ARPANET router, called an Interface Message Processor . This connection and protocol is generally referred to as 1822, the report number....
.
Since lower protocol layers were provided by the IMP-host interface, NCP essentially provided a Transport Layer
Transport layer
In computer networking, the transport layer or layer 4 provides end-to-end communication services for applications within a layered architecture of network components and protocols...
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
File Transfer Protocol
File Transfer Protocol is a standard network protocol used to transfer files from one host to another host over a TCP-based network, such as the Internet. FTP is built on a client-server architecture and utilizes separate control and data connections between the client and server...
) accessed network services through an interface to the top layer of the NCP, a forerunner to the Berkeley sockets
Berkeley sockets
The Berkeley sockets application programming interface comprises a library for developing applications in the C programming language that perform inter-process communication, most commonly for communications across a computer network....
interface.
Transition to TCP/IP
On January 1, 1983, known as flag dayFlag day (software)
Flag day, as used in system administration, is a change which requires a complete restart or conversion of a sizable body of software or data. The change is large and expensive, and—in the event it doesn't work—reversing the change is similarly difficult and expensive.This usage originates from a...
, 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.