DSL and Networks Information

Digital subscriber line technology was originally implemented as part of the ISDN specification, which is later reused as IDSL. Higher speed DSL connections like HDSL and SDSL have been developed to extend the range of DS1 services on copper lines. Consumer oriented ADSL is designed to operate also on a BRI ISDN line, which itself is a form of DSL, as well as on an analog phone line.DSL, like many other forms of communication, stems directly from Claude Shannon’s seminal 1948 scientific paper: A Mathematical Theory of Communication. Employees at Bellcore (now Telcordia Technologies) developed ADSL in 1988 by placing wideband digital signals above the existing baseband analog voice signal carried between telephone company central offices and customers on conventional twisted pair cabling.U.S. telephone companies promote DSL to compete with cable modems. DSL service was first provided over a dedicated “dry loop”, but when the FCC required the incumbent local exchange carriers ILECs to lease their lines to competing providers such as Earthlink, shared-line DSL became common. Also known as DSL over Unbundled Network Element , this allows a single pair to carry data (via a digital subscriber line access multiplexer [DSLAM]) and analog voice (via a circuit switched telephone switch) at the same time. Inline low-pass filter/splitters keep the high frequency DSL signals out of the user’s telephones. Although DSL avoids the voice frequency band, the nonlinear elements in the phone would otherwise generate audible intermodulation products and impair the operation of the data modem.Older ADSL standards can deliver 8 Mbit/s to the customer over about 2 km (1.25 miles) of unshielded twisted pair copper wire. The latest standard, ADSL2+, can deliver up to 24 Mbit/s, depending on the distance from the DSLAM. Distances greater than 2 km (1.25 miles) significantly reduce the bandwidth usable on the wires, thus reducing the data rate. By using an ADSL loop extender, these distances can be increased substantially.In 2007, Dr. John Papandriopoulos, a University of Melbourne engineering researcher, patented algorithms that can potentially boost DSL line speeds to a maximum of 250 Mbit/s.