After all, DSL data speeds are often a fraction of those offered by cable broadband suppliers. Plus, DSL (Digital Subscriber Line) is delivered not over coax, but over old-fashioned copper phone lines. How quaint!
But a seemingly low-bandwidth DSL connection could actually deliver data faster than a higher-rated broadband cable connection, according to the father of DSL, Dr. John Cioffi.
“DSL brings its entire data load to a SINGLE home,” Dr. Cioffi explains. “Cable systems share their Internet bandwidth – typically 50 Mbps to 300 Mbps – across 500 to 2000 homes. Thus, 50 Mbps divided by 2000 homes simultaneously is indeed a very low speed kbps. Each DSL user has a much higher dedicated bandwidth.”
Advancing and proselytizing DSL has been a passion and a mission for Dr. Cioffi, but there was no early inkling of what would become his life’s work.
The young Cioffi, a math whiz, got a taste of his future on a family trip to the New York World’s Fair in 1964 when he watched a demonstration of AT&T’s videophone. “They thought it was impossible to send video over phone lines,” Dr. Cioffi recalls. “It planted a seed.”
What turned Dr. Cioffi’s career toward DSL was a physics course he took as a freshman at the University of Illinois Urbana–Champaign. Originally a mechanical engineering major, Dr. Cioffi switched to electrical engineering when he discovered his math skills made a more practical impact. And those skills were evident: Dr. Cioffi aced the highest-level graduate classes as a sophomore and graduated in 1978 as the engineering school valedictorian. Bell Labs quickly hired him and paid for his graduate work at Stanford University.
Dr. Cioffi spent six years shuttling cross country between Bell Labs’ Holmdel, New Jersey, facilities and Palo Alto, California, to Stanford, where he earned both his master’s and PhD in electrical engineering. At both Bell and Stanford, Dr. Cioffi worked to quadruple the speed of 2400 bps early half-duplex voiceband modems, and soon earned a reputation for getting things to work. Bell Labs soon called him to help solve echo cancellation problems in the new public switched digital network, the beginnings of DSL.
But the real goal in Dr. Cioffi’s mind was not pushing low bandwidth digital voice data through copper lines, but high data rate digital video.
Unfortunately, the divestiture of the Bell System in 1984 divested Dr. Cioffi of his nascent DSL thoughts. So Dr. Cioffi joined IBM’s San Jose lab to work on increasing the bit rate capacity of the computer company’s disk drives.
But in early 1986, Stanford made Dr. Cioffi an offer he couldn’t refuse: to continue his work as an assistant professor of electrical engineering, researching and teaching the science of increasing speeds on wired and wireless media through the use of digital signal processing.
The seven Baby Bells also continued to work on DSL, but none seemed to move forward. Dr. Cioffi realized why: the Baby Bells had been following a so-called single-carrier method, a technical dead-end.
Instead, Dr. Cioffi, with PhD candidates including Tony Ruiz, Sanjay Kasturia, Jim Aslanis, Peter Chow, Jacky Chow, Minnie Ho, Huiling Lou, and Jerry Tu, developed an alternative, more adaptive single-carrier modulation technique called Discrete Multi-Tone (DMT) modulation, also known as bit-swapping, which divides frequencies into separate “carriers” and “subcarriers” to transmit discrete data channels.
Using DMT, Dr. Cioffi and his students managed to push DSL data speeds first to 1.5 Mbps, then to 6 Mbps, “good enough” for video.
In 1991, Dr. Cioffi took a leave of absence from Stanford and, along with Peter Chow and Jacky Chow and other friends from the industry including John Bingham, Mark Flowers, and Mark Mallory, founded Amati Communications to build DSL modems. In Spring 1992, Dr. Cioffi and Amati faced a deadline: in January 1993, there would be a DSL “Olympics” in Miami, Florida, to determine an industry DSL standard. Dr. Cioffi’s competition, which included AT&T/Lucent, Bellcore and Broadcom, did not believe he and his team would be ready.
They were wrong.
Amati’s Prelude ADSL modem could now transmit 6 Mbps-plus, four times the speeds of other proposed designs. Under the watchful eye of ANSI chair Thomas Starr, the decision by the 200-plus voters was unanimous.
“As I walked out of the door to the large conference hall, there was a line as far as I could see all the way into the lobby far away,” Cioffi remembers. “It took me a few minutes to understand: they were all there to shake the hand of the little guy/start-up who had just taken it to the largest telecommunication powers in the world and won. It was kind of unprecedented, and that line made me realize what had really just happened. I came into work [the next day] and there were yellow ribbons all around my office upon my return to California. We all knew what it meant.”
On 10 March 1993, 117 years to the day after Alexander Graham Bell yelled “Watson come here I need you,” Dr. Cioffi’s DMT-based DSL technology was declared the U.S. standard, followed by the European Union standards group a few months later and the ITU a year later.
In 1995, Amati went public, then was bought by Texas Instruments in 1997. While continuing to work at Amati and TI, Dr. Cioffi returned to Stanford to work on numerous outstanding DSL issues. To counter nagging crosstalk noise problems, for instance, Dr. Cioffi and his new group of PhD students developed Dynamic Spectrum Management (DSM) and, in 2000, “vectoring,” which combined to more efficiently delineate signal from noise generated by household appliances to better eliminate the latter and help squeeze more bits through the copper lines.
In 2003, Dr. Cioffi founded ASSIA (Adaptive Spectrum and Signal Alignment), an acronym that is also his wife’s name, which develops and licenses DSM solutions for 31 telcos around the world, servicing nearly 100 million DSL subscribers.
Thanks to Cioffi, now professor emeritus at Stanford and fulltime CEO of ASSIA, DSL can now deliver hundreds of megabits per second and even gigabits over copper wire. Nearly 75 percent of broadband-connected homes around the world now connect to the Internet via DSL – most of them getting data far faster than seemingly faster cable broadband connections.