Leonard Kleinrock

Leonard Kleinrock is an American computer scientist whose research in queueing theory and packet switching helped establish the Internet’s technical foundations.

J. C. R. Licklider: J. C. R. Licklider was an American psychologist and computer scientist who promoted interactive computing and networked computers. As an early ARPA leader, he shaped the research environment in which Kleinrock’s networking ideas developed.
ARPANET: ARPANET was an early packet-switched computer network funded by the United States Department of Defense. Kleinrock’s UCLA computer became ARPANET’s first node, and his group operated its Network Measurement Center.
Queueing theory: Queueing theory is the mathematical study of waiting lines, service processes, and congestion. Kleinrock used it to analyze communication networks, including delays and capacity under competing traffic.
Information Flow in Large Communication Nets: “Information Flow in Large Communication Nets” is Kleinrock’s 1961 doctoral dissertation on message flow in communication networks. The dissertation developed mathematical foundations for analyzing communication networks and their performance.
Circuit switching: Circuit switching reserves a dedicated communication path between endpoints for the duration of a connection. It contrasts with the shared links and independently routed packets Kleinrock’s networking research examined.
Larry Roberts: Larry Roberts was an American computer scientist who led the design and deployment of ARPANET. Roberts drew on Kleinrock’s work when planning ARPANET’s packet-switched network.
Interface Message Processor: The Interface Message Processor was a packet-switching computer that connected host computers to ARPANET. The first IMP was installed at Kleinrock’s UCLA laboratory, making his site ARPANET’s first connection.
Packet switching: Packet switching sends data as separately addressed units that share network links and are reassembled at their destination. It is the networking approach Kleinrock analyzed and helped establish as a practical alternative to dedicated circuits.
Communication Nets: Stochastic Message Flow and Delay: “Communication Nets: Stochastic Message Flow and Delay” is Kleinrock’s 1964 book on queueing models for communication networks. This book made his analysis of message flow and network delay a systematic foundation for later work.
End-to-end principle: The end-to-end principle places many communication functions at network endpoints rather than inside the network core. Packet networks influenced by Kleinrock’s work made a relatively simple core and capable endpoints practical.

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Ray TomlinsonRelated: Packet switching made the network environment possible for Tomlinson's intercomputer messaging.