The first ADSL standard was ratified in by ANSI in 1996 followed by an internationally recognized ITU G.992.1 and G.992.2 standards in 1999.  By 2000 there were 5 million ADSL subscribers.  Shortly after launching ADSL, the ITU-T committee realized that, while the standard was a great starting point, it still needed improvements in several areas, and they set to work on ADSL2.  By 2002, the ADSL2 standard was approved and the industry hailed the extended rate and reach as the defining technologies needed to effectively compete with the cable modem market.

The ITU standard, G.bond, also known as “Bonded ADSL2+,” was introduced in early 2005 as a way to double the downstream data rate of copper pairs.  VDSL was ratified in 2003, but service providers interested in expanding their offerings concluded that more work was needed on the new standard in order to support advanced services. VDSL2 showed the potential of much higher data rates for enhanced service features, so the ITU-T continued to refine the details for the next-generation of the standard. Shortly after the world celebrated the milestone of 100 million DSL subscribers globally, VDSL2 (G.993.2) was consented in May 2005, and officially approved in May 2006.

G.shdsl, also known as G.991.2, was developed in 2001 for symmetric business class voice and data services and delivering greater symmetric bandwidth over longer distances than T1 systems, As an international standard, G.shdsl has the benefits of multi-vendor interoperability and spectral compatibility with other DSL technologies.  G.shdsl supports symmetric data rates up to 2.3 Mbps over a single copper pair. The payload can be comprised of traditional T1 Time Domain Multiplexing (TDM) 64-kbps time slots or ATM cells. The G.shdsl standard also defines provisions for combining TDM and ATM traffic.

History of DSL Standards and Their Impact on the DSL Market

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