The ARPANET was initiated as a four-node network in Dec. 1969, and has evolved via DARPANET into the present Internet.

The impetus for the ARPANET came from a small group of workers in universities and private research laboratories in the USA, who were funded by the US Department of Defense Advanced Research Project Agency to create a data network that was capable of continuing to function even when parts of the network were destroyed. The solution proposed relied on the use of packet switching, which was implemented by small dedicated computers called interface message processors (IMPs), and used a distributed routing algorithm to manage the movement of self-contained packets of data between their source and destination.

ARPANET pioneered many of the network concepts now in current use, including the use of layered protocols. Each protocol governs the transfer of information for a range of associated applications, and delegates the control of the traffic flow to cooperating processes located either at the end-user applications, or, for the lower layers of the protocol, to processes located in the switching nodes.