In 1984, Cioffi left Bell Labs to work at
IBM as a
hard disk drive read channel researcher. In 1986, Cioffi began his teaching career as an assistant professor of electrical engineering at Stanford University. Cioffi supervised the Ph.D. programs of more than 70 students over the course of more than two decades. His and his students' research into
discrete multitone modulation (DMT) became widely adopted in
digital subscriber line (DSL) technology, used commonly for
Internet access. In 1991, at the age of 35, Cioffi took a leave of absence from Stanford to found Amati Communications Corporation. His vision was to build DSL modems based on his and his students' research. Many of Cioffi's then-current and former students followed him to Amati, where they built the Prelude modem, a DSL modem that could transmit 6+ megabits per second over of
telephone line. The Prelude modem would go on to win what has become known as the "Bellcore ADSL Olympics" in 1993 by performing significantly better than modems using single-carrier modulation techniques, such as
quadrature amplitude modulation (QAM) and
carrierless amplitude phase modulation (CAP), including modems from
AT&T and
Bellcore. Hundreds of millions of people now use DSL based on Amati's innovations. In 1993, Cioffi returned to Stanford, although he remained involved with Amati as an officer and director until its 1998 acquisition by
Texas Instruments. Cioffi's research interests then turned to
dynamic spectrum management (DSM), an improvement on DSL that mitigates service interruptions and allows DSL lines to run with higher and more reliable data rates. In 2001, Cioffi was elected as a member into the
National Academy of Engineering for contributions to the theory and practice of high-speed digital communications. In 2003, Cioffi founded Adaptive Spectrum and Signal Alignment, Inc. (ASSIA) to help service providers realize improvements in the performance and profitability of their DSL networks. Today ASSIA's customers collectively provide DSL service to more than 70 million subscribers worldwide. In 2009, Cioffi assumed
emeritus status at Stanford, as the Hitachi Professor Emeritus of Engineering. He is now CEO and Chairman of ASSIA. ==Honors and awards==