ARPANET was a packet-switched network developed by DARPA and MIT in the late 1960s. It allowed for reliable bi-directional communication and introduced protocols such as email and FTP. In 1983, it merged with other networks to form the Internet, using TCP/IP and application protocols from ARPANET. It was decommissioned in 1990.
The Advanced Research Projects Agency Network (ARPANET) was one of the major forerunners of the Internet. At the time it was conceived, most communications were thought of in terms of circuit switching, but the ARPANET implemented the kind of packet-switched network that would dominate communications worldwide. The network was based on the principle of creating small packets of data that could be sent across the network link whenever it was available, rather than protecting a circuit, as would be required in a circuit switched network.
ARPANET began as a project of the United States Department of Defense (DoD). It was initially developed by teams at the Defense Advanced Research Projects Agency (DARPA) and the Massachusetts Institute of Technology (MIT). The ideas behind a packet-switched network date back to the early 1960s, although the Defense Advanced Research Projects Agency (DARPA) network itself wasn’t designed and implemented until the latter part of that decade.
The first computers connected via ARPANET were located at Stanford University, the University of Utah and two campuses of the University of California. Each campus had a computer known as an interface message processor (IMP) that functioned similar to a modern router. They each then connected both a Scientific Data Systems (SDS) and International Business Machines (IBM) or Digital Equipment Corporation (DEC) computer to the IMP and through it to the ARPANET. These four nodes comprised the entire network at the end of 1969.
To reliably communicate data bi-directionally, the Network Control Program (NCP) was designed. This has effectively allowed various applications to communicate across the network. Various application protocols were created throughout the 1970s. E-mail was introduced to the network in 1971, and file transfer protocol (FTP) was implemented in 1973. A voice transfer protocol, known as network voice protocol (NVP), was also created, although bandwidth of the network has hindered its use.
In 1983, NCP was replaced by the modern Transmission Control Protocol/Internet Protocol (TCP/IP) when the ARPANET integrated with other networks to form the first Internet. Many of the existing application protocols, such as FTP, have been ported to the suite of protocols used by the Internet. Also in 1983, the US military portions of the network were split to create the Discreet Military Network (MILNET).
ARPANET operated continuously from 1969 until it was decommissioned in 1990. The last IMPs went offline in the late 1980s and ARPANET was merged with a number of other networks to form the backbone of what would become known as the Internet. These networks used the common TCP/IP protocol as well as a number of application protocols first introduced on the ARPANET.
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