Kleinrock made several important contributions to the field of computer science, in particular to the theoretical foundations of data communicationincomputer networking. He has received numerous prestigious awards.
In the early 1960s, Kleinrock pioneered the application of queueing theory to model delays in message switching networks in his Ph.D. thesis, published as a book in 1964. In the late 1960s and 1970s, he played an influential role in the development of the ARPANET. In the 1970s, he applied queueing theory to model and measure the performance of packet switching networks and published several of the standard works on the subject. He supervised graduate students who worked on the communication protocols for the ARPANET including students whose later work on internetworking and the Internet protocol suite led to the networking technology employed in the Internet. His theoretical work on hierarchical routing in the late 1970s with student Farouk Kamoun remains critical to the operation of the Internet today.
Kleinrock's best-known and most-significant work is on queueing theory, a major topic of applied mathematics that has applications in many fields. His thesis proposal in 1961, Information Flow in Large Communication Nets, led to a doctoral thesis at MIT in 1962, Message Delay in Communication Nets with Storage, later published as book in 1964, Communication Nets: Stochastic Message Flow and Design. In this work, he researched the configuration and operation of communication networks, considering design parameters such as "channel capacity, effect of priority discipline, choice of routing procedure, and design of topological structure". He analyzed delays in Plan 55-A, a message switching system operated by Western Union for processing telegrams. His thesis went on to apply probability theory to model queueing delays in a generalized communication network.[5][6]
Donald Davies, in his 1966 paper on packet switching, applied Kleinorck's techniques to show that "there is an ample margin between the estimated performance of the [packet-switched] system and [Davies'] stated requirement" in terms of a response time satisfactory to a human user.[7] This addressed a key question about the viability of computer networking.[8]
A contemporary from MIT, Larry Roberts, brought Leonard Kleinrock into the ARPANET project informally in early 1967.[9] Roberts learned about packet switching from a paper written by Davies, presented at the October 1967 Symposium on Operating Systems Principles, and incorporated the concept into the proposal for the ARPANET.[10][11][12][13] Kleinrock was awarded a contract in 1968 to establish a Network Measurement Center (NMC) to measure and model the performance of the network.[14] His mathematical work studied and influenced the development of the early ARPANET.[5][15][16][17] In addition, Kleinrock managed the software team at UCLA — including Steve Crocker, Jon Postel, and Vint Cerf — who developed the host-host protocol for the ARPANET, the Network Control Program (NCP).[18]
The first message on the ARPANET was sent by a UCLA undergraduate student, Charley Kline, who was supervised by Kleinrock.[19][20] At 10:30 p.m, on October 29, 1969, from Boelter Hall 3420, the school's main engineering building, Kline transmitted from the university's SDS Sigma 7 host computer to the Stanford Research Institute's SDS 940 host computer. The message text was the word "login"; the "l" and the "o" letters were transmitted, but the system then crashed. Hence, the literal first message over the ARPANET was "lo". About an hour later, having recovered from the crash, the SDS Sigma 7 computer effected a full "login".[21][22] The first permanent ARPANET link was established on November 21, 1969, between the Interface Message Processor (IMP) at UCLA and the IMP at the Stanford Research Institute. By December 5, 1969, the initial four-node network was established.[23][24]
Kleinrock used the ARPANET for instant messaging from the U.S. to Larry Roberts in England in 1973, employing the network for a modern every-day use.[25]
Kleinrock published hundreds of research papers,[26][27] which ultimately launched a new field of research on the theory and application of queueing theory to computer networks.[5][28][29][30] In this role, he supervised the research of scores of graduate students.[27][31] He disseminated his research and that of his students to wider audiences for academic and commercial use, and organized hundreds of commercial seminars presented by experts and pioneers in the U.S. and internationally.[31][27] Many graduate students that Kleinrock supported based their careers on expertise they acquired while working on the ARPANET with him, including several whose later work on internetworking and the Internet protocol suite led to the networking technology employed in the Internet.[8][28] Kleinrock's work published in the mid-1970s on the performance of the ARPANET, which was discussed at the International Network Working Group,[32] underpinned the development of the Transmission Control Protocol of the Internet protocol suite.[33][34] His analytic work in the 1970s addressed packet switching networks, packet radio networks, local area networks, broadband networks, nomadic computing, peer-to-peer networks, and intelligent software agents.[26] Kleinrock's theoretical work on hierarchical routing with student Farouk Kamoun remains critical to the operation of the Internet today.[35][36]
The thing that really drove my own research was the idea of a message switching network, which was a precursor to the packet switching networks. The mathematical tool that had been developed in queueing theory, namely queueing networks, matched perfectly the model of computer networks. Actually, it didn't match perfectly and I had to adjust that model to fit the realities of computer networks. Then I developed some design procedures as well for optimal capacity assignment, routing procedures and topology design.
Beginning in the mid-1990s, Kleinrock sought to be recognized "as the father of modern data networking".[42] By 1997, he claimed priority on the invention of packet switching and to have convinced Larry Roberts to adopt the technique.[43] In 2004, he described his work as:
Basically, what I did for my PhD research in 1961-1962 was to establish a mathematical theory of packet networks which uncovered the underlying principles that drives today's Internet.
However, Kleinrock's claims that his work in the early 1960s originated the concept of packet switching and that his work was a source of the packet switching concepts used in the ARPANET are disputed by other Internet pioneers,[42][44][45][46] including Robert Taylor,[47]Paul Baran,[48] and Donald Davies.[49] Historians and the U.S. National Inventors Hall of Fame recognize Baran and Davies for independently inventing the concept of digital packet switching used in modern computer networking including the Internet.[10][11][50][51][52]
Kleinrock made several important contributions to the field of computer science, in particular to the theoretical foundations of data communicationincomputer networking. He has received numerous professional awards. In 1980, he was elected a member of the National Academy of Engineering for pioneering contributions to the field and leadership as an educator in computer communications networks.[53] In 2001 he received the Draper Prize "for the development of the Internet".[54] Kleinrock was selected to receive the prestigious National Medal of Science, the nation's highest scientific honor, from President George W. Bush in the White House on September 29, 2008. "The 2007 National Medal of Science to Leonard Kleinrock for his fundamental contributions to the mathematical theory of modern data networks, and for the functional specification of packet switching, which is the foundation of Internet technology. His mentoring of generations of students has led to the commercialization of technologies that have transformed the world."[1]
In 2010 he shared the Dan David Prize.[55] UCLA Room 3420 at Boelter Hall was restored to its condition of 1969 and converted into the Kleinrock Internet Heritage Site and Archive. It opened to the public with a grand opening attended by Internet pioneers on October 29, 2011.[22][56]
He was elected as a member into the National Academy of Engineering. In 2012, Kleinrock was inducted into the Internet Hall of Fame by the Internet Society.[26] Leonard Kleinrock was inducted into IEEE-Eta Kappa Nu (IEEE-ΗΚΝ) in 2011 as an Eminent Member. The designation of Eminent Member is the organization's highest membership grade and is conferred upon those select few whose outstanding technical attainments and contributions through leadership in the fields of electrical and computer engineering have significantly benefited society. He was elected to the 2002 class of Fellows of the Institute for Operations Research and the Management Sciences.[57] In September 2014, Leonard Kleinrock was awarded the ACM SIGMOBILE Outstanding Contribution Award at MobiCom 2014.
Leonard Kleinrock was given the 2014 BBVA Foundation Frontiers of Knowledge Award "for his seminal contributions to the theory and practical development of the Internet," in the words of the jury's citation.[58]
In 2014, a special edition of Computer Networks was published in his honor. Articles were written in recognition of Kleinrock's contributions to queueing theory, packet switching, computer communication networks and the development of the Internet and related network technologies.[59]
^ abcClarke, Peter (1982). Packet and circuit-switched data networks(PDF) (PhD thesis). Department of Electrical Engineering, Imperial College of Science and Technology, University of London. "Many of the theoretical studies of the performance and design of the ARPA Network were developments of earlier work by Kleinrock ... Although these works concerned message switching networks, they were the basis for a lot of the ARPA network investigations ... The intention of the work of Kleinrock [in 1961] was to analyse the performance of store and forward networks, using as the primary performance measure the average message delay. ... Kleinrock [in 1970] extended the theoretical approaches of [his 1961 work] to the early ARPA network."
^ abHafner, Katie; Lyon, Matthew (1996). Where wizards stay up late : the origins of the Internet. Internet Archive. New York : Simon & Schuster. pp. 76–78. ISBN978-0-684-81201-4. Roger Scantlebury ... from Donald Davies' team ... presented a detailed design study for a packet switched network. It was the first Roberts had heard of it. ... Roberts also learned from Scantlebury, for the first time, of the work that had been done by Paul Baran at RAND a few years earlier.
^Abbate, Janet (1999). Inventing the Internet. Internet Archive. MIT Press. pp. See page refs highlighted at url. ISBN978-0-262-01172-3. On Kleinrock's influence, see Frank, Kahn, and Kleinrock 1972, p. 265; Tanenbaum 1989, p. 631.
^Roberts, Lawrence G.; Wessler, Barry D. (1970). "Computer network development to achieve resource sharing". Proceedings of the May 5-7, 1970, spring joint computer conference on - AFIPS '70 (Spring). New York, NY, USA: Association for Computing Machinery. pp. 543–549. doi:10.1145/1476936.1477020. ISBN978-1-4503-7903-8. S2CID9343511. The third paper by Kleinrock [5] derives procedures for optimizing the capacity of the transmission facility in order to minimize cost and average message delay. ... [5] L KLEINROCK. Analytic and simulation methods in Computer Network Design AFIPS Conference Proceedings, May 1970
^Still, tapping into the ARPANET to fetch a shaver across international lines was a bit like being a stowaway on an aircraft carrier. The ARPANET was an official federal research facility, after all, and not something to be toyed with. Kleinrock had the feeling that the stunt he'd pulled was slightly out of bounds. 'It was a thrill. I felt I was stretching the Net'. – "Where Wizards Stay Up Late: The Origins of the Internet", Chapter 7.
^Davies, Donald Watts (1979). Computer networks and their protocols. Internet Archive. Wiley. pp. See page refs highlighted at url. ISBN978-0-471-99750-4. In mathematical modelling use is made of the theories of queueing processes and of flows in networks, describing the performance of the network in a set of equations. ... The analytic method has been used with success by Kleinrock and others, but only if important simplifying assumptions are made. ... It is heartening in Kleinrock's work to see the good correspondence achieved between the results of analytic methods and those of simulation.
^Davies, Donald Watts (1979). Computer networks and their protocols. Internet Archive. Wiley. pp. 110–111. ISBN978-0-471-99750-4. Hierarchical addressing systems for network routing have been proposed by Fultz and, in greater detail, by McQuillan. A recent very full analysis may be found in Kleinrock and Kamoun.
^Feldmann, Anja; Cittadini, Luca; Mühlbauer, Wolfgang; Bush, Randy; Maennel, Olaf (2009). "HAIR: Hierarchical architecture for internet routing"(PDF). Proceedings of the 2009 workshop on Re-architecting the internet. ReArch '09. New York, NY, USA: Association for Computing Machinery. pp. 43–48. doi:10.1145/1658978.1658990. ISBN978-1-60558-749-3. S2CID2930578. The hierarchical approach is further motivated by theoretical results (e.g., [16]) which show that, by optimally placing separators, i.e., elements that connect levels in the hierarchy, tremendous gain can be achieved in terms of both routing table size and update message churn. ... [16] KLEINROCK, L., AND KAMOUN, F. Hierarchical routing for large networks: Performance evaluation and optimization. Computer Networks (1977).
^ abIsaacson, Walter (2014). The Innovators: How a Group of Hackers, Geniuses, and Geeks Created the Digital Revolution. Simon & Schuster. pp. 244–6. ISBN9781476708690. This led to an outcry among many of the other Internet pioneers, who publicly attacked Kleinrock and said that his brief mention of breaking messages into smaller pieces did not come close to being a proposal for packet switching ... until the mid-1990s, Kleinrock had credited [Baran and Davies] with coming up with the idea of packet switching
^Harris, Trevor, University of Wales (2009). Pasadeos, Yorgo (ed.). "Who is the Father of the Internet? The Case for Donald Davies". Variety in Mass Communication Research. ATINER: 123–134. ISBN978-960-6672-46-0. Archived from the original on May 2, 2022. Leonard Kleinrock and Lawrence (Larry) Roberts, neither of whom were directly involved in the invention of packet switching ... Dr Willis H. Ware, Senior Computer Scientist and Research at the RAND Corporation, notes that Davies (and others) were troubled by what they regarded as in appropriate claims on the invention of packet switching{{cite journal}}: CS1 maint: multiple names: authors list (link)
^Haughney Dare-Bryan, Christine (June 22, 2023). Computer Freaks (Podcast). Chapter Two: In the Air. Inc. Magazine.
^Katie Hefner (November 8, 2001), "A Paternity Dispute Divides Net Pioneers", New York Times, The Internet is really the work of a thousand people," Mr. Baran said. "And of all the stories about what different people have done, all the pieces fit together. It's just this one little case that seems to be an aberration.
^Abbate, Jane (2000). Inventing the Internet. MIT Press. pp. 37–8, 58–9. ISBN978-0262261333. The NPL group influenced a number of American computer scientists in favor of the new technique, and they adopted Davies's term "packet switching" to refer to this type of network. Roberts also adopted some specific aspects of the NPL design.
Kleinrock, Leonard (3 April 1990). "Oral history interview with Leonard Kleinrock". University of Minnesota, Minneapolis: Charles Babbage Institute. Retrieved 15 May 2008. Kleinrock discusses his work on the ARPANET; his dissertation work in queueing theory; and his move to the University of California at Los Angeles (UCLA). As one of the main contractors for the ARPANET, Kleinrock describes his involvement in discussions before the official DARPA request was issued, the people involved in the ARPANET work at UCLA, the installation of the first node of the network, the Network Measurement Center, and his relationships with Lawrence Roberts and the IPT Office, Bolt, Beranek and Newman, and the Network Analysis Corporation.