The TCP/IP model (Transmission Control Protocol/Internet Protocol) is a model with four layers which is for both modelling current Internet architecture, as well as providing a set a rules that govern all forms of transmission over a network. DARPA, an agency of the United States Department of Defense,created it in the 1970s. It evolved from ARPANET, which was an early wide area network and a predecessor of the Internet. The TCP/IP Model is sometimes called the "Internet Model" or less often the "DoD Model."