n worst competitor. But even without TELPAK, resale of leased lines was a vital tool for smaller switched long distance competitors. While MCI had built much of its own net- work and initially could not sell Execunet calls to areas where it did not have facilities, resale meant that AT&T's own leased lines could be used by switched long distance competitor. In 1981, the FCC finalized sharing of WATS-type services too, which by that point were all measured-use anyway, albeit at a discount from retail tolls. Resale was important for the long distance telephone industry, but it was even more important for the development of the Internet. In the 1970s, the Department of Defense's (DoD) Advanced Research Projects Agency had financed the development of the ARPAnet, a worldwide packet-switched data network that later became the core of the Internet. The ARPAnet was techni- cally not resale; it was the DoD's and was only used for government-related pur- poses. (This was construed rather loosely, but data network research was considered a valid government-related activity, as were many other private and university-related activities.) Other corporations built private data networks too, but the first public data network providers, such as Telenet and Tymnet, were technically common carriers until Computer II deregulated them. Unlimited sharing and resale later allowed the development of multiple ARPAnet-like data networks, under different ownership, as well as the provisioning of lines between The Great Telecom Meltdown corporations. This was a prerequisite for the eventual development of the Inter- net itself. The ENFIA Agreement Made Subsidies Explicit Once switched competition was held permissible by the judiciary, the FCC had to figure out how to regulate it. AT&T and the independent local telephone companies were both threatened; the old system of separations and settlements that dated back to the Smith decision depended on keeping toll rates higher than cost in order to hold down local service rates. Execunet had bee