In 1973, Vint Cerf and Bob Kahn sketched out the Transmission Control Protocol in a hotel lobby, attempting to solve the problem of connecting incompatible networks without requiring any of them to change. The insight was to make the endpoints — not the network — responsible for reliability: the network would do its best to deliver packets, and if it failed, the endpoints would notice and retry. This end-to-end principle, seemingly modest, turned out to be the design decision that made the internet extensible, resilient, and extraordinarily difficult to centrally control — a property that has been simultaneously its greatest strength and a persistent frustration for governments ever since. The original TCP specification was 84 pages. The network it described now carries several exabytes of data per day.
