ISI became one of the earliest nodes on ARPANET, the predecessor to the Internet, and in 1977 figured prominently in a demonstration of its international viability. ISI also helped refine the TCP/IP communications protocols fundamental to Net operations, and researcher Paul Mockapetris developed the now-familiar Domain Name System characterized by .com, .org, .net, .gov, and .edu on which the Net still operates. (The names .com, .org et al. were invented at SRI International, an ongoing collaborator.) Steve Crocker originated the Request for Comments (RFC) series, the written record of the network's technical structure and operation that both documented and shaped the emerging Internet. Another ISI researcher, Danny Cohen, became first to implement packet voice and packet video over ARPANET, demonstrating the viability of packet switching for real-time applications.