June 13, 1934 — Leonard Kleinrock Is Born

The vast majority of modern networks — mobile, local, and otherwise — rely on packet switching. The idea of transmitting data between computers without dedicating an entire communication channel to a single connection, instead breaking information into smaller units called packets, was developed independently in the mid-20th century by three researchers: Paul Baran, Donald Davies, and Leonard Kleinrock.

Paul Baran worked on methods of maintaining communications during a nuclear war. Donald Davies coined the term “packet” to describe the structure used for transmitting information. Leonard Kleinrock developed the mathematical model that demonstrated packet switching could work efficiently in practice.

Kleinrock was born on June 13, 1934, in New York City. In the early 1960s, he began studying the problem of data transmission between computers. At the time, computers were expensive machines that operated largely in isolation. The idea of connecting them into networks was only beginning to take shape.

In 1961, he published the paper Information Flow in Large Communication Nets, applying queueing theory to computer networks.

These studies later formed the basis of his book Communication Nets (1964). Kleinrock showed that data could be transmitted efficiently in small pieces across a shared network, rather than allocating a dedicated communication channel for every connection as telephone systems did. His work provided the mathematical foundation for the development of packet-switched networks.

Kleinrock was also one of the most active participants in the development of ARPANET. The first ARPANET node was installed in his laboratory at UCLA. Between the 1960s and the 1990s, he conducted research on network protocols, routing, network performance, and mobile communications. He also trained several generations of engineers and computer scientists at UCLA.