Research into packet switching started in the early 1960s,[15] and packet switched networks such as the ARPANET, CYCLADES,[16][17] the Merit Network,[18] NPL network,[19] Tymnet, and Telenet, were developed in the late 1960s and 1970s using a variety of protocols.[20] The ARPANET project led to the development of protocols for internetworking, by which multiple separate networks could be joined into a single network of networks.[21]