Kleinrock, Leonard

Kleinrock, Leonard

(1934–  ) American

Engineer, Computer Scientist

Every day billions of e-mails, text messages, and media files are sent over the worldwide Internet. The infrastructure that allows the efficient transmission of this vast data traffic is largely based on the system of packet-switching and rout-ing invented by Leonard Kleinrock.

Kleinrock was born in 1934 and grew up in New York City. When he was only six years old Kleinrock built a crys-tal radio, the first of many electronics projects, built from cannibalized old radios and other equipment. Kleinrock attended the Bronx High School of Science, home of many of the nation’s top future engineers. However, when it came time for college, the family had no money to pay for his higher education, so he attended night courses at the City College of New York while working as an electronics techni-cian and later as an engineer. Kleinrock graduated first in his class in 1957 and earned a fully paid fellowship to the Massachusetts Institute of Technology.

At MIT Kleinrock became interested in finding ways for computers and their users to communicate with each other. The idea of computer networking was in its infancy, but he submitted a proposal in 1959 for Ph.D. research in network design.

In 1961 Kleinrock published his first paper, “Informa-tion Flow in Large Communication Nets.” Existing tele-phone systems did what was called “circuit switching”: To establish a conversation, the caller’s line is connected to the receiver’s, forming a circuit that existed for the duration of the call. This also meant that the circuit would not be available to anyone else, and that if something was wrong with the connection there was no way to route around the problem.

Kleinrock’s basic idea was to set up data connections that would be shared among many users as needed. Instead of the whole call (or data transmission) being assigned to a particular circuit, it would be broken up into packets that could be sent along whatever circuit was the most direct. If there was a problem, the packet could be resent on an alternative route. This form of “packet switching” provided great flexibility as well as more efficient use of the avail-able circuits. Kleinrock further elaborated his ideas in his dissertation, for which he was awarded his Ph.D. in 1963. The following year MIT published his book Communications Nets, the first full treatment of the subject.

Kleinrock joined the faculty at the University of Cali-fornia, Los Angeles. In 1968 the Defense Department’s Advanced Research Projects Agency (ARPA) asked him to design a packet-switched network that would be known as ARPANET. The computers on the network would be con-nected using special devices called Interface Message Pro-cessors (IMPs). The overall project was under the guidance and supervision of one of Kleinrock’s MIT office mates, Lawrence Roberts.

On October 29, 1969, Kleinrock and his assistants sent the first data packets between UCLA and Stanford over phone lines. Their message, the word “login,” was hardly as dramatic as Alexander Graham Bell’s “Watson, come here, I need you!” Nevertheless, a form of communication had been created that in a few decades would change the world as much as the telephone had done a century earlier.

The idea of computer networking did not catch on imme-diately, however. Besides requiring a new way of thinking about the use of computers, many computer administrators were concerned that their computers might be swamped with users from other institutions, or that they might ulti-mately lose control over the use of their machines. Klein-rock worked tirelessly to convince institutions to join the nascent network. By the end of 1969 there were just four ARPANET “nodes”: UCLA, the Stanford Research Institute,

UC Santa Barbara, and the University of Utah. By the fol-lowing summer, there were ten. During the 1970s Kleinrock trained many of the researchers who would advance the technology of network-ing. While Kleinrock’s first network was not the Internet we know today, it was an essential step in its development. In successfully establishing communication using the packet-switched ARPANET, Kleinrock showed that such a network was practicable.

By the early 1990s Kleinrock was looking toward a future where most network connections were wireless and accessi-ble through a variety of computerlike devices such as hand-held “palmtop” computers, cell phones, and others not yet imagined. In such a network the intelligence or capability is distributed throughout, with devices communicating seam-lessly so the user no longer need be concerned about what particular gadget he or she is using. By the middle of the fol-lowing decade, much of this vision had become reality.

Although his name is not well known to the general public, Kleinrock has won considerable recognition within the technical community. This includes Sweden’s L. M. Ericsson Prize (1982), the Marconi Award (1986), and the National Academy of Engineering Charles Stark Draper Prize (2001).