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Advance in the DSL technology
The DSL technology is classified as below according to the advance in the technology

ISDN(Integrated Services Digital Network)
One of the technology developed in 1980's. This technology is developed in order to send voice and data through one telephone line. Using an electrical transmission form called 2B1Q, ISDN transmitted 160kbps of data in 80kHz of bandwidth and the transmission range was about 5~6Km. Used mostly in European nation such as Germany and Japan, but not as much in USA. The reason is relatively complicated terminal configuration and expensive service fee; however, if used as a part of the system IDSL in the future, ISDN can create a huge market demand.

HDSL(High bit rate DSL)
One of the technology developed in 1980's. This technology is developed in order to send voice and data through one telephone line. Using an electrical transmission form called 2B1Q, ISDN transmitted 160kbps of data in 80kHz of bandwidth and the transmission range was about 5~6Km. Used mostly in European nation such as Germany and Japan, but not as much in USA. The reason is relatively complicated terminal configuration and expensive service fee; however, if used as a part of the system IDSL in the future, ISDN can create a huge market demand.

SDSL(Single Line DSL or Symmetric DSL)
An abbreviation used for two methods. One uses HDSLtechnology but uses one pair of telephone lines. This technology is called HDSL. The other uses ADSL technology but synchronizes the downstream and upstream speed. However, this technology can assure limited transmission speed (around 1Mbps) and transmission range because of the cross talk which can affect the system.

SHDSL(Single Line High bit rate DSL)
G.shdsl stands for Symmetric High Bit Rate Digital Subscriber Loop and is defined by the new ITU Global Standard as defined in ITU G991.2 from February 2001. G.shdsl provides high symmetric data rates with guaranteed bandwidth and low interference with other services. By supporting equal upstream and downstream data rates, it has the ability to combine multiple voice and data channels within the G.shdsl payload.

ADSL(Asymmetrical DSL)
Set as a Standard by ANSI(USA) and ETSI(Europe), this method is known as a revolutionary technology that can provide more than one service with just one pair of telephone lines. This provides the maximum of more than 6Mbps transmission speed. From now on, ASSL is thought to be vital part for the multimedia service for future users. However, that kind of wide-area service is not developed yet, and it will be very expensive for the subscribers. Recently, many communication companies such as Compaq, Intel and MicroSoft are working together to set the UADSL(Universal ADSL) technology standard, and say that the result will come in this year.

VDSL(Very High Bit Rate DSL)
Advanced form of ADSL technology that can support a transmission speed of about 25Mbps ~ 50Mbps. In the future, VDSL will be connected to networks such as FTTC(Fiber To The Curb) and FTTB(Fiber To The Building) and used for services that requires a high bandwidth; however, VDSL is still in the area of future technology today.