 Leonard Kleinrock worked on the application of queueing theory to message switching (in the early 1960s) and packet switching (in the early 1970s).His initial contribution to this field was his doctoral thesis at the Massachusetts Institute of Technology in 1962, published in book form in 1964 in the field of message switching.His theoretical work published in the early 1970s underpinned the use of packet switching in the ARPANET, a forerunner to the Internet.