DSL (Digital Subscriber Lines) Connection

DSL is the acronym for Digital Subscriber Lines. DSL technologies use sophisticated modulation schemes to pack data onto copper wires. They are sometimes referred to as last-mile technologies because they are used only for connections from a telephone switching station to a home or office, not between switching stations. DSL is similar to ISDN in as much as both operate over existing copper telephone lines and both require the short runs to a central telephone office (usually less than 20,000 feet). However, DSL offers much higher speeds—up to 32 Mbps for upstream traffic (client to server) , and from 32 Kbps to over I Mbps for downstream traffic (server to client).

There two main categories being

■ Asymmetric digital subscriber line (ADSL)
■ Symmetric digital subscriber line (SDSL)

Depending upon the speed some also classify as follows:

■ High-data-rate DSL (HDSL)
■ Very high DSL (VDSL).

Asymmetric Digital Subscriber Line (ADSL)

Asymmetric digital subscriber line is a new technology that allows more data to be sent over existing copper telephone lines. ADSL supports data transfer downstream rate from 1.5 to 9 Mbps and upstream rate from 16 to 640 Kbps. ADSL requires a special ADSL modem. ADSL. growing in popularity as more areas around the world gain access to Internet.

Symmetric Digital Subscriber Line (SDSL)

Symmetric digital subscriber line is a technology that allows more data to be sent over existing copper telephone lines. SDSL supports data rates up to 3 Mbps. SDSL works by sending digital pulses in the high-frequency area of telephone wires. Since these high frequencies are not used by normal voice communications, SDSL can operate simultaneously with voice connections ove: the same wires. SDSL requires a special SDSL modem. SDSL is called symmetric because supports the same data rates for upstream and downstream traffic. ADSL is more popular in North America , whereas SDSL is being developed primarily in Europe. A comparison of ADSI and SDSL is shown in Table 1.1.2.