While pursuing his doctorate in computer science, Metcalfe took a job with MIT's Project MAC after Harvard refused permission for him to connect the university to the then-new ARPAnet. At MAC, Metcalfe was responsible for building some of the hardware that would link MIT's minicomputers with ARPAnet. Metcalfe made ARPAnet the topic of his doctoral thesis, but Harvard initially rejected it. Metcalfe decided how to improve his thesis while working at Xerox PARC, where he read a paper about the ALOHA network at the University of Hawaii. He identified and fixed some of the bugs in the AlohaNet model, then added that work to his revised thesis. It was then accepted by Harvard, which granted his PhD.

Metcalfe was working at PARC in 1973 when he and David Boggs invented Ethernet, initially as a standard for connecting computers over short distances. He later recalled that Ethernet was born on May 22, 1973, the day he circulated a memo titled "Alto Ethernet" which contained a rough schematic of how it would work. "That is the first time Ethernet appears as a word, as does the idea of using coax as ether, where the participating stations, like in AlohaNet or ARPAnet, would inject their packets of data, they'd travel around at megabits per second, there would be collisions, and retransmissions, and back-off," Metcalfe explained. Boggs argued that another date was the birth of Ethernet: November 11, 1973, the first day the system actually functioned.

In 1979, Metcalfe departed PARC and co-founded 3Com, a manufacturer of computer networking equipment, in his Palo Alto apartment. 3Com became a leading provider of networking solutions, and Ethernet became the dominant networking standard for local area networks (LANs). In 1980 he received the ACM Grace Hopper Award for his contributions to the development of local networks, specifically Ethernet. In 1990, the 3Com board of directors appointed Éric Benhamou as CEO instead of Metcalfe, who then left the company. He spent 10 years as a publisher and pundit, writing an internet column for InfoWorld. In 1996, he co-founded Pop!Tech, an executive technology conference. He became a venture capitalist in 2001 and subsequently a general partner at Polaris Venture Partners.

From 2011 to 2021 he was a professor at The University of Texas at Austin's Cockrell School of Engineering, specializing in innovation initiatives. Metcalfe was a keynote speaker at the 2016 Congress of Future Science and Technology Leaders and in 2019 he presented the Bernard Price Memorial Lecture in South Africa. In June 2022, Metcalfe returned to MIT by joining the Computer Science and Artificial Intelligence Laboratory as a research affiliate and computational engineer, working with the MIT Julia Lab.
What was Robert Metcalfe's impact on society?
Robert Metcalfe was a successful entrepreneur, having started companies like 3Com and Pop!Tech. He was also a professor at the University of Texas and a researcher at the Massachusetts Institute of Technology. His biggest contribution, however, was the invention of Ethernet in 1973. This became the standard for wired internet connection, which is still used 50 years later.