 ITU-T G.SHDSL regional variant for Europe. It is important to be aware that equip- ment referred to as supporting SDSL is generally proprietary equipment that talks only to SDSL equipment from the same vendor or another vendor that uses the same DSL chipset. However, most new installations use the standardized G.SHDSL equipment instead of the older SDSL. G.SHDSL Two main drivers influenced the introduction of G.SHDSL. First, the industry observed that there was a need for a higher-speed digital transport service for busi- ness applications. HDSL was available but had never been adopted as an interna- tional standard. Second, SDSL, which was introduced in the late 1990s as the business-class DSL service, never became a standard, and it also posed problems in that it interfered with the residential ADSL service, being very noisy and therefore spectrally incompatible with ADSL (i.e., creating difficulties when deployed in the same cable bundle as ADSL). A global standard was therefore needed. G.SHDSL was developed to incorporate the features of other DSL technologies, such as ADSL and SDSL, and it can transport T-1, E-1, ISDN, ATM, and IP signals. G.SHDSL, often referred to as simply SHDSL, was the first international stan- dard for DSL, originally ratified by the ITU-T in February 2001 in recommendation G.991.2. The standard was then updated in 2003, and that version is referred to as G.991.2bis. It is compatible with the ETSI SDSL and ANSI HDSL2 standards. This is more important than it may seem on the surface: A worldwide standard allows for global mass deployment, and higher volumes worldwide mean lower equip- ment prices. G.SHDSL is a symmetrical service with options to operate over one pair or two pairs of copper wires, and it also has rate-adaptive capability. Symmetric band- width, an increasingly desirable characteristic, supports advanced applications that require high performance in both directions. G.SHDSL supports data rates up 5.6Mbps in each direction. G.SHDSL eliminates the need for T-1/E-1 repeater