History of DSL
| Digital Subscriber Line |
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A method for moving data over regular phone lines. A DSL circuit is much faster than a regular phone connection, and the wires coming into the subscriber's premises are the same (copper) wires used for regular phone service. A DSL circuit must be configured to connect two specific locations, similar to a leased line (howeverr a DSL circuit is not a leased line. A common configuration of DSL allows downloads at speeds of up to 1.544 megabits (not megabytes) per second, and uploads at speeds of 128 kilobits per second. This arrangement is called ADSL: Asymmetric Digital Subscriber Line. Another common configuration is symmetrical: 384 Kilobits per second in both directions. In theory ADSL allows download speeds of up to 9 megabits per second and upload speeds of up to 640 kilobits per second. DSL is now a popular alternative to Leased Lines and ISDN, being faster than ISDN and less costly than traditional Leased Lines. See also: ADSL, Bandwidth, ISDN, Leased Line, SDSL While the theoretical capacity of copper to transmit data was long known, the practical use of telephone wires for high speed data was first demonstrated in the late 1980s. Joseph Lechleider, now retired from Bellcore, through mathematical analysis demonstrated the feasibility of sending broadband signals, and is considered by many the originator of all these technologies. He went on to suggest the power of asymmetry, (the A in ADSL), recognizing many users would benefit from the higher data rates possible in one direction. His colleagues speak of him with great fondness, and he inspired many of the other pioneers in the field.The editor of DSL Prime would appreciate photocopies of any of his seminal papers from the late '80s or early '90s. The first efforts created ISDN and then the two circuit replacement for T-1 lines that came to be called HDSL. ISDN never was effectively marketed in the US, but remains popular in Europe. HDSL, on the other hand, was very successful, and is used for most T-1 circuits installed today. In the early 1990s, many sought a way to deliver broadband to more users. John Cioffi, now a Stanford Professor, developed DMT, the standard for most DSL circuits. By separating the signal into 256 subchannels, many problems relating to line noise and disturbance can be minimized. He founded Amati, where they designed equipment that in 1993 had dramatically better results than all competitors in Bellcore testing and became the most common standard. Several of his competitors to this day think it was not the best technical solution at the time, but carried the day because of Cioffi's personal brilliance. They blame other companies for not putting appropriate resources into other technologies, and the success of Broadcom, whose founders were major participants, speaks to the alternatives. While these debates were raging at Bellcore, standards committees, and technical journals, others were impatient to bring product to the market. The dream was to deliver video on demand, a telco goal while the cable world was promising 500 channels. Kim Maxwell, also of Amati, was a key founder of the ADSL Forum, which brought the industry together and today is the key institution. But while the technologists believed deployment was practical, little happened in the field, so an alliance was formed between telcos and computer companies (Intel and Compaq, especially) which became the UAWG and developed the G.Lite standard. G.Lite is coming to market in late 1999, and aims to reduce the installation and other costs of DSL. When DSL was first developed in 1989, it was designed primarily for video. ADSL was the flavor of choice because it provides the high downstream rates needed for streaming video. Video on Demand (VOD) was viewed as the next generation service supporting the next generation network from telephone companies around the world. Video on Demand was expected to be the telephone company's way of competing with cable television providers, and ADSL was the technology to make it possible. However, with few exceptions, VOD has not proven to be as popular as was once predicted. Instead, the market for DSL has emerged much differently than was once expected. As it turns out, personal computer users need high-speed access to the Internet and corporate networks from residences and remote offices. Now, this PC user market has captured the attention of both cable TV providers and telephone companies, as both are furiously working to meet their needs |
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