<P> For a long time, it was thought that it was not possible to operate a conventional phone - line beyond low - speed limits (typically under 9600 bit / s). In the 1950s, ordinary twisted - pair telephone - cable often carried four megahertz (MHz) television signals between studios, suggesting that such lines would allow transmitting many megabits per second . One such circuit in the United Kingdom ran some ten miles (16 km) between the BBC studios in Newcastle - upon - Tyne and the Pontop Pike transmitting station . It was able to give the studios a low quality cue feed but not one suitable for transmission . However, these cables had other impairments besides Gaussian noise, preventing such rates from becoming practical in the field . </P> <P> The 1980s saw the development of techniques for broadband communications that allowed the limit to be greatly extended . A patent was filed in 1979 for the use of existing telephone wires for both telephones and data terminals that were connected to a remote computer via a digital data carrier system . The motivation for digital subscriber line technology was the Integrated Services Digital Network (ISDN) specification proposed in 1984 by the CCITT (now ITU - T) as part of Recommendation I. 120, later reused as ISDN digital subscriber line (IDSL). Employees at Bellcore (now Telcordia Technologies) developed asymmetric digital subscriber line (ADSL) by placing wide - band digital signals above the existing baseband analog voice signal carried between telephone company telephone exchanges and customers on conventional twisted pair cabling facilities, and filed a patent in 1988 . </P> <P> Joseph W. Lechleider's contribution to DSL was his insight that an asymmetric arrangement offered more than double the bandwidth capacity of symmetric DSL . This allowed Internet service providers to offer efficient service to consumers, who benefited greatly from the ability to download large amounts of data but rarely needed to upload comparable amounts . ADSL supports two modes of transport--fast channel and interleaved channel . Fast channel is preferred for streaming multimedia, where an occasional dropped bit is acceptable, but lags are less so . Interleaved channel works better for file transfers, where the delivered data must be error - free but latency (time delay) incurred by the retransmission of error - containing packets is acceptable . </P> <P> Consumer - oriented ADSL was designed to operate on existing lines already conditioned for Basic Rate Interface ISDN services, which itself is a digital circuit switching service (non-IP), though most incumbent local exchange carriers (ILECs) provision rate - adaptive digital subscriber line (RADSL) to work on virtually any available copper pair facility, whether conditioned for BRI or not . Engineers developed high speed DSL facilities such as high bit rate digital subscriber line (HDSL) and symmetric digital subscriber line (SDSL) to provision traditional Digital Signal 1 (DS1) services over standard copper pair facilities . </P>

Dsl data transmission is faster than a t1 line