From 1966-1969 he was Assistant Director of Research at Cambridge, where in 1967 he designed and implemented the Titan computer's file system, and worked on file archival, privacy, and persistent names. He moved to AT&T Bell Laboratories in 1969 where he invented cell-based networks that anticipated Asynchronous Transfer Mode (ATM) and co-developed a reduced instruction set computer prototype with techniques for instruction set optimization. He subsequently became director of its Computing Science Research Center (1982), Executive Director (1987), and Associate Vice President for Information Science Research (1994). As Vice President for Research, he founded AT&T Laboratories in 1996, and in 1998 was named AT&T Chief Scientist. After his retirement in 2002 he established Fraser Research.