Paul Baran, an engineer who helped create the technical underpinnings for the ARPAnet, the government-sponsored precursor to today's Internet, died Saturday night at his home in Palo Alto. He was 84.

The cause was complications from lung cancer, said his son, David.

In the early 1960s, while working at the Rand Corp. in Santa Monica, Baran outlined the fundamentals for packaging data into discrete bundles, which he called "message blocks." The bundles are then sent on various paths around a network and reassembled at their destination. Such a plan is known as "packet switching."

Baran's idea was to build a distributed communications network, less vulnerable to attack or disruption than conventional networks. In a series of technical papers published in the 1960s he suggested that networks be designed with redundant routes so that if a particular path failed or was destroyed, messages could still be delivered through another.

Baran's invention was so far ahead of its time that in the mid-1960s, when he approached AT&T with the idea to build his proposed network, the company insisted it would not work and refused.

"Paul wasn't afraid to go in directions counter to what everyone else thought was the right or only thing to do," said Vinton Cerf, a vice president at Google who was a colleague and longtime friend of Baran's. "AT&T repeatedly said his idea wouldn't work, and wouldn't participate in the ARPAnet project," he said.


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In 1969, the Department of Defense's Advanced Research Projects Agency built the ARPAnet, a network that used Baran's ideas and those of others. The ARPAnet was eventually replaced by the Internet, and packet switching still lies at the heart of the network's internal workings.

Paul Baran was born on April 29, 1926, in Grodno, Poland. His parents moved to the United States in 1928, and Baran grew up in Philadelphia. His father was a grocer, and as a boy, Paul delivered orders to customers in a small red wagon.

He attended the Drexel Institute of Technology, which later became Drexel University, where he earned a bachelor's degree in electrical engineering in 1949. He took his first job at the Eckert-Mauchly Computer in Philadelphia, testing parts of radio tubes for an early commercial computer, the UNIVAC. In 1955, he married Evelyn Murphy, and they moved to Los Angeles, where Baran took a job at Hughes Aircraft working on radar data processing systems. He enrolled in night classes at UCLA.

Baran received a master's degree in engineering from UCLA in 1959. Gerald Estrin, who was Baran's adviser, said Baran was the first student he ever had who actually went to the Patent Office in Washington to investigate whether his master's work, on character recognition, was patentable.

"From that day on, my expectations of him changed," Estrin said. "He wasn't just a serious student, but a young man who was looking to have an effect on the world."

In 1959, Baran left Hughes to join Rand's computer science department. He quickly developed an interest in the survivability of communications systems in the event of a nuclear attack, and spent the next several years at Rand working on a series of 13 papers -- two of them classified -- under contract to the Air Force, titled, "On Distributed Communications."

In recent years, the origins of the Internet have been subject to claims and counterclaims of precedence, and Baran was an outspoken proponent of distributing credit widely.

"The Internet is really the work of a thousand people," he said in an interview in 2001.