Internet Precursor Created
In 1973, American engineers Vint Cerf and Bob Kahn began designing a new way for different computer networks to talk to one another. Their work led to TCP/IP, the set of rules that still underpins the internet. The date is often given as the moment ARPANET adopted TCP/IP, but that is a simplification. The design began in 1973, and ARPANET did not switch over until early 1983. The earlier year marks the conceptual birth of the "internet" rather than its launch.
The background lies in ARPANET, a research network funded by the U.S. Defense Department's Advanced Research Projects Agency. It carried its first messages in 1969, linking a handful of university and research computers. It relied on packet switching, in which data is split into small chunks that travel independently and are reassembled at their destination. The idea drew on work by Paul Baran, Donald Davies, and others. ARPANET grew quickly, and by the early 1970s other networks were appearing, including radio-based and satellite-based packet networks, each with its own technical conventions.
The problem was that these networks could not easily interconnect. Kahn, working at ARPA, wanted a way to link them without forcing any to change its internal workings. He teamed with Cerf, then at Stanford, and in 1973 they developed the concept of a common protocol that would run on top of the different networks. They presented their ideas that year, and a landmark paper describing the design appeared in 1974. The original single protocol was later split into two layers: IP, which handles addressing and routing of packets, and TCP, which ensures data arrives complete and in order. Meanwhile, ARPANET also made its first international links around 1973, connecting to sites in Norway and the United Kingdom. Separately, Robert Metcalfe and colleagues at Xerox PARC were developing Ethernet for local networks.
Several years of testing and refinement followed. Multiple versions of the protocols were tried, and in 1983 ARPANET formally switched to TCP/IP. That change is widely treated as the start of the operational internet. Through the 1980s, networks such as the National Science Foundation's NSFNET connected universities, and the system spread beyond the military and research communities.
The legacy of the 1973 design is its openness and flexibility. Because TCP/IP does not depend on any particular hardware or network type, it could absorb new technologies, from fiber optics to Wi-Fi to mobile phones. The World Wide Web, invented by Tim Berners-Lee around 1989, is an application built on top of it, not the internet itself. Cerf and Kahn received the Turing Award in 2004 for their work, a recognition of how a design sketched in the early 1970s grew into global infrastructure.