Leonard Kleinrock
Headshot of Leonard Kleinrock
Born (1934-06-13) June 13, 1934 (age 90)
Alma materCity College of New York, MIT
Known forQueueing theory, ARPANET, Internet development
Scientific career
Doctoral advisorEdward Arthurs[2]
Claude Shannon
Doctoral studentsChris Ferguson

Leonard Kleinrock (born June 13, 1934) is an American computer scientist and Internet pioneer. He is Distinguished Professor Emeritus of Computer Science at UCLA's Henry Samueli School of Engineering and Applied Science. Kleinrock made several important contributions to the field of computer science, in particular to the mathematical foundations of data communication in computer 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.

Education and career

Leonard Kleinrock was born in New York City on June 13, 1934, to a Jewish family,[3] and graduated from the noted Bronx High School of Science in 1951. He received a Bachelor of Electrical Engineering degree in 1957 from the City College of New York, and a master's degree and a doctorate (Ph.D.) in electrical engineering and computer science from the Massachusetts Institute of Technology (MIT) in 1959 and 1963 respectively. He then joined the faculty at the University of California at Los Angeles (UCLA), where he remains to the present day; during 1991–1995 he served as the chairman of the Computer Science Department there.[4]


Queueing theory

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 the stated requirement" in terms of a satisfactory response time for 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 asked Frank Westervelt to explore the questions of message size and contents for the network, and to write a position paper on the intercomputer communication protocol including “conventions for character and block transmission, error checking and retransmission, and computer and user identification."[10] Later that year, 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.[11][12][13][14]

Kleinrock was awarded a contract in 1968 to establish a Network Measurement Center (NMC) to measure and model the performance of the network.[15] His mathematical work studied and influenced the development of the early ARPANET.[5][16][17][18] 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).[19]

The first message on the ARPANET was sent by a UCLA undergraduate student,[20] Charley Kline, who was supervised by Kleinrock.[21][22] 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".[20][23] 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.[24][25]

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.[26][27]


Kleinrock published hundreds of research papers,[28][29] which ultimately launched a new field of research on the theory and application of queueing theory to computer networks.[5][30][31][32] In this role, he supervised the research of scores of graduate students.[29][33] 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.[33][29] 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][30] Kleinrock's work published in the mid-1970s on the performance of the ARPANET, which was discussed at the International Network Working Group,[34] underpinned the development of the Transmission Control Protocol of the Internet protocol suite.[35][36][37] 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.[28] Kleinrock's theoretical work on hierarchical routing with student Farouk Kamoun remains critical to the operation of the Internet today.[38][39]

In 1988, Kleinrock was the chairman of a group that presented the report Toward a National Research Network to the U.S. Congress, concluding that "There is a clear and urgent need for a national research network".[40] Although the U.S. did not build a nationwide national research and education network, this report influenced Al Gore to pursue the development of the High Performance Computing Act of 1991,[41] which helped facilitate development of the Internet as it is known today.[42] Funding from the bill was used in the development of the 1993 web browser Mosaic at the National Center for Supercomputing Applications (NCSA), which accelerated the adoption of the World Wide Web.[43][44]

Packet switching 'paternity dispute'

Further information: Packet switching § The "paternity dispute"

In 1990, Kleinrock said:[33]

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".[45] By 1997, he claimed priority on the invention of packet switching and to have convinced Larry Roberts to adopt the technique.[46] 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,[45][47][48][49] including Robert Taylor,[50] Paul Baran,[51] and Donald Davies.[52] 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.[11][12][53][54][55]

Awards and recognition

2012 Internet Hall of Fame inductees, including Leonard Kleinrock (seated, fifth from the left)

Kleinrock made several important contributions to the field of computer science, in particular to the mathematical foundations of data communication in computer 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.[56] In 2001 he received the Draper Prize "for the development of the Internet".[57] 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.[58] 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.[23][59]

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.[28] 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.[60] 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.[61]

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.[62]

See also



  1. ^ a b "Eight National Medals of Science Awardees Honored at Gala". NSF. 26 September 2008. Retrieved 19 May 2012.
  2. ^ Leonard Kleinrock at the Mathematics Genealogy Project
  3. ^ "Jews in Computer & Information Science". The Jewish Contribution to World Civilization web site. Retrieved 5 July 2011.
  4. ^ "Leonard Kleinrock's Profile". UCLA. 12 April 2011. Retrieved 24 May 2012.
  5. ^ a b c Clarke, 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."
  6. ^ Kleinrock, Leonard (December 1962). Message Delay in Communication Nets with Storage (PDF) (Thesis). Cambridge: Massachusetts Institute of Technology.
  7. ^ Davies, D. W. (1966). "Proposal for a Digital Communication Network" (PDF). p. 10, 16.
  8. ^ a b Heart, F.; McKenzie, A.; McQuillian, J.; Walden, D. (January 4, 1978). Arpanet Completion Report (PDF) (Technical report). Burlington, MA: Bolt, Beranek and Newman. pp. III-40-1
  9. ^ "SRI Project 5890-1; Networking (Reports on Meetings). [1967]". web.stanford.edu. Archived from the original on 2011-08-10. Retrieved 2020-02-15. W. Clark's message switching proposal (appended to Taylor's letter of April 24, 1967, to Engelbart )were reviewed.
  10. ^ Pelkey, James. "4.7 Planning the ARPANET: 1967-1968 in Chapter 4 - Networking: Vision and Packet Switching 1959 - 1968". The History of Computer Communications. Archived from the original on December 23, 2022. Retrieved May 9, 2023.
  11. ^ a b "The real story of how the Internet became so vulnerable". Washington Post. Archived from the original on 2015-05-30. Retrieved 2020-02-18. Historians credit seminal insights to Welsh scientist Donald W. Davies and American engineer Paul Baran
  12. ^ a b Hafner, Katie; Lyon, Matthew (1996). Where wizards stay up late : the origins of the Internet. Internet Archive. New York : Simon & Schuster. pp. 76–78. ISBN 978-0-684-81201-4. 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.
  13. ^ Moschovitis, Christos J. P (1999). History of the Internet: a chronology, 1843 to the present. Internet Archive. ABC-CLIO. ISBN 978-1-57607-118-2.
  14. ^ Roberts, L.G. (1978). "The evolution of packet switching". Proceedings of the IEEE. 66 (11): 1307–1313. doi:10.1109/PROC.1978.11141. ISSN 1558-2256. S2CID 26876676.
  15. ^ "Leonard Kleinrock Helps Build The ARPANET". Living Internet. Retrieved 2021-03-19.
  16. ^ Abbate, Janet (1999). Inventing the Internet. Internet Archive. MIT Press. pp. See page refs highlighted at url. ISBN 978-0-262-01172-3. On Kleinrock's influence, see Frank, Kahn, and Kleinrock 1972, p. 265; Tanenbaum 1989, p. 631.
  17. ^ 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. ISBN 978-1-4503-7903-8. S2CID 9343511. 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
  18. ^ Kahn, R.E. (1972). "Resource-sharing computer communications networks". Proceedings of the IEEE. 60 (11): 1397–1407. doi:10.1109/PROC.1972.8911. ISSN 0018-9219. 7. H. Frank, R. E. Kahn and L. Kleinrock, "Computer communication network design—experience with theory and practice", AFIPS Spring Joint Comput. Conf., pp. 255-270, 1972.
  19. ^ Meeting of the ARPA Computer Network Working Group at UCLA, November 16, 1967
  20. ^ a b Beranek, Leo (2000). "Roots of the Internet: A Personal History". Massachusetts Historical Review. 2: 55–75. ISSN 1526-3894. JSTOR 25081152.
  21. ^ Orr, Tamra B. (2019-07-15). The Information Revolution: Transforming the World Through Technology. Greenhaven Publishing LLC. ISBN 978-1-5345-6786-3.
  22. ^ Rosenbaum, Philip (29 October 2009). "Web pioneer recalls 'birth of the Internet'". CNN. Retrieved October 30, 2009.
  23. ^ a b Savio, Jessica (1 April 2011). "Browsing history: A heritage site is being set up in Boelter Hall 3420, the room the first Internet message originated in". UCLA Daily Bruin. UCLA. Archived from the original on 5 January 2012. Retrieved 1 April 2011.
  24. ^ Sutton, Chris. "Internet Began 35 Years Ago at UCLA with First Message Ever Sent Between Two Computers". UCLA. Archived from the original on 8 March 2008. Retrieved 1 April 2011.
  25. ^ Kleinrock tells the story of the first Internet connection (UCLA video)
  26. ^ "TALKING HEADERS". Washington Post. 2024-01-07. ISSN 0190-8286. Retrieved 2024-06-19.
  27. ^ 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.
  28. ^ a b c "Leonard Kleinrock". Internet Hall of Fame. Retrieved 2023-03-13.
  29. ^ a b c "Kleinrock (Leonard) papers". oac.cdlib.org. Retrieved 2023-04-04.
  30. ^ a b Abbate, Janet (1999). Inventing the Internet. Internet Archive. MIT Press. p. 81. ISBN 978-0-262-01172-3.
  31. ^ Davies, Donald Watts (1979). Computer networks and their protocols. Internet Archive. Wiley. pp. See page refs highlighted at url. ISBN 978-0-471-99750-4. 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.
  32. ^ Kleinrock, L. (1978). "Principles and lessons in packet communications". Proceedings of the IEEE. 66 (11): 1320–1329. doi:10.1109/PROC.1978.11143. ISSN 0018-9219.
  33. ^ a b c O'Neill, Judy (3 April 1990). "An Interview with Leonard Kleinrock" (PDF). pp. 7, 13–15.
  34. ^ "General Notes index: 1-77, 98-111, 116-125 citing note number, author, and title; INWG Protocol Notes index: 1-10, 28-38 citing note number, author, title and date". umedia.lib.umn.edu. Retrieved 2024-05-29.
  35. ^ Cerf, Vinton (March 1977). "Specification of Internet Transmission Control Program: TCP (Version 2)" (PDF). p. 96.
  36. ^ Cerf, Vinton G.; Postel, Jon (January 1978). "Specification of Internetwork Transmission Program: TCP Verison 3" (PDF). p. 81.
  37. ^ Postel, Jon (September 1978). "Specification of Internetwork Transmission Control Protocol: TCP Version 4" (PDF). pp. 91–2.
  38. ^ Davies, Donald Watts (1979). Computer networks and their protocols. Internet Archive. Wiley. pp. 110–111. ISBN 978-0-471-99750-4. 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.
  39. ^ 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. ISBN 978-1-60558-749-3. S2CID 2930578. 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).
  40. ^ Toward a National Research Network. National Academies Press. 1988. p. 39. doi:10.17226/10334. ISBN 978-0-309-58125-7.
  41. ^ "High-Performance Computing Act of 1991". Archived from the original on 19 October 2015. Retrieved 21 March 2011.
  42. ^ "A Bill of Rights for the Internet: What Should it Have Been at the Outset" (PDF). Retrieved 21 March 2011.
  43. ^ Tuutti, Camille (23 September 2011). "R&D in IT essential to help US stay competitive". Federal Computer Week. Retrieved 25 May 2012.
  44. ^ Vetter, Ronald J. (October 1994). "Mosaic and the World-Wide Web" (PDF). North Dakota State University. Archived from the original (PDF) on August 24, 2014. Retrieved November 20, 2010.
  45. ^ a b Isaacson, Walter (2014). The Innovators: How a Group of Hackers, Geniuses, and Geeks Created the Digital Revolution. Simon & Schuster. pp. 244–6. ISBN 9781476708690. 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
  46. ^ "Brief History of the Internet" (PDF). Internet Society. 1997. p. 3.
  47. ^ Alex McKenzie (2009), Comments on Dr. Leonard Kleinrock's claim to be "the Father of Modern Data Networking", retrieved April 23, 2015 "... there is nothing in the entire 1964 book that suggests, analyzes, or alludes to the idea of packetization."
  48. ^ 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. ISBN 978-960-6672-46-0. 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)
  49. ^ Haughney Dare-Bryan, Christine (June 22, 2023). Computer Freaks (Podcast). Chapter Two: In the Air. Inc. Magazine.
  50. ^ Robert Taylor (November 22, 2001), "Birthing the Internet: Letters From the Delivery Room; Disputing a Claim", New York Times, Authors who have interviewed dozens of Arpanet pioneers know very well that the Kleinrock-Roberts claims are not believed.
  51. ^ 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.
  52. ^ Donald Davies (2001), "A Historical Study of the Beginnings of Packet Switching", Computer Journal, British Computer Society, 44 (3): 152–162, doi:10.1093/comjnl/44.3.152, I can find no evidence that he understood the principles of packet switching.[dead link]
  53. ^ Abbate, Jane (2000). Inventing the Internet. MIT Press. pp. 37–8, 58–9. ISBN 978-0262261333. 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.
  54. ^ Pelkey, James L.; Russell, Andrew L.; Robbins, Loring G. (2022). Circuits, Packets, and Protocols: Entrepreneurs and Computer Communications, 1968-1988 (PDF). Morgan & Claypool. p. 4. ISBN 978-1-4503-9729-2. Paul Baran, an engineer celebrated as the co-inventor (along with Donald Davies) of the packet switching technology that is the foundation of digital networks
  55. ^ "Inductee Details - Paul Baran". National Inventors Hall of Fame. Archived from the original on 6 September 2017. Retrieved 6 September 2017; "Inductee Details - Donald Watts Davies". National Inventors Hall of Fame. Archived from the original on 6 September 2017. Retrieved 6 September 2017.
  56. ^ "Dr. Leonard Kleinrock". NAE Website. Retrieved 2021-07-01.
  57. ^ "Draper Prize Honors Four 'Fathers of the Internet'". Wall Street Journal. February 12, 2001. Retrieved 5 September 2017.
  58. ^ Wileen Wong Kromhout (March 15, 2010). "UCLA Internet pioneer Leonard Kleinrock looks toward future, helps students do the same". UCLA Engineering. Archived from the original on April 21, 2010. Retrieved March 30, 2011.
  59. ^ McCarty, Meghan (19 July 2011). "Beginning of the Internet commemorated in new UCLA museum". Southern California Public Radio. Retrieved 21 July 2011.
  60. ^ Fellows: Alphabetical List, Institute for Operations Research and the Management Sciences, archived from the original on 2019-05-10, retrieved 2019-10-09
  61. ^ "Leonard Kleinrock". Premios Fronteras. Retrieved 2022-06-28.
  62. ^ Silvester, John, and Parviz Kermani. “Professor Leonard Kleinrock – Tribute Volume.” Computer networks (Amsterdam, Netherlands : 1999) 66 (2014): 1–3.