DSL

DSL (Digital Subscriber Line) technology uses normal telephone lines to provide broadband services. This is possible because DSL internet handles digital signals which are not susceptible to noise and interference as analog systems.

The essence of the DSL system lies in end-to-end conversion of the existing system of carrying signals from the central office of the telephone company to the consumer. The telephone company installs a DSLAM to connect their lines to the ISP (Internet Service Provider), and a DSL Modem or DSL Router at the consumer end of their line. The system is now equipped to handle the digital signals up to the consumer end. The consumer equipment is connected through the DSL Modem to the internet.

Typically DSL speeds range from 256 kbps (256,000 bits per second) to 24Mbps (24,000,000 bits per second) depending on the type of technology used. Two commonly used versions of this service are the SDSL and the ADSL. SDSL (Symmetric DSL) provides internet service capable of download or upload speeds of up to 1.4 Mbps. ADSL (Asymmetric DSL) can provide download speeds of up to 1.4Mpbs but upload speeds of only up to 640 kbps and also facilitate simultaneous voice communication which is not provided by SDSL system.

SDSL system is intended for small businesses that have a large amount of data that needs to be uploaded while additional voice communication facility is not a necessity. ADSL on the other hand is intended more for home users who have greater need of downloads such as of music, videos and much lesser requirement of uploads excepting e-mails.

Apart from the DSL & ADSL, there are other types of DSL services such as VDSL &RADSL, etc. VDSL (Very high bit rate DSL) provides a fast connection but over a very short distance from the central office of the telephone company. RADSL (Rate-adaptive DSL) is a system which the modem can adjust the speed of communication depending on the length and quality of the line. These systems, however, are not very common.

One important point to note is that the system of DSL connections is limited to locations which are within a radius of about 18,000 feet (5,460 meters) from the service provider.
It is obvious that DSL internet service can be provided only where telephone lines exist. There are many DSL providers such as Verizon DSL, AT&T DSL, Yahoo DSL, Bellsouth DSL, SBC Yahoo DSL, SBC DSL Free DSL and others. Their systems basically are similar but territories served, tariff structures may be different. Since so much depends upon the internet speed, one can always carry out a DSL speed test. Generally the service providers do have a provision for it; if not these facilities are available from organizations such as C/Net.