The DSL technology was meant to deliver video to its users and was the dream of Telecommunication Services Providers since more than a decade. The technology was realized when there was a demand from consumers for high speed internet access.

DSL is a broadband communication technology that provides for high speed access to the Internet and remote networks using phone lines that are already present. It utilizes frequencies that are out of the frequency band dedicated to the plain old telephone service (POTS) ? PSTN, ISDN, as normal voice and fax services are called.

There are country variations in the exact frequency ranges used, e.g. in Europe:
• PSTN 0-4 kHz
• ISDN 0-80 kHz (Germany ? 120 kHz)
• ADSL 138-1100 kHz

b) xDSL OPERATIONS

xDSL utilizes more of the bandwidth on the copper phone line than what is currently used for POTS; therefore it has the capacity to encode more data to achieve higher data rates than is otherwise possible in the restricted frequency range of a POTS network. In order to utilize the frequencies above the voice audio spectrum, and provide both POTS and DSL services on the same phone lines, special equipment must be installed at both ends (i.e. at residence and in the Telecom operator Central Office (CO)). The device usually installed in the home is called a router. It is used to separate the frequencies of the telephone audio spectrum from the frequencies of the xDSL signals, to allow the simultaneous usage of the line for the telephone as well as to access the Internet.

Several forms of xDSL have emerged designed around specific needs and objectives.

Some of the standards are:
• ADSL Asymmetric Digital Subscriber Line (Full rate)
• Asymmetric Digital Subscriber Line (G.Lite)
• RADSL Rate-Adaptive Asymmetric Digital Subscriber Line
• HDSL High Data Rate Digital Subscriber Line
• SHDSL Single Pair High Data Rate Digital Subscriber Line
• IDSL ISDN Digital Subscriber Line
• VDSL Very High Data Rate Digital Subscriber Line

Currently the most popular DSL form in use is the Asymmetric Digital Subscriber Line (ADSL). The basic characteristic of ADSL is the difference between the upstream and downstream bandwidth, hence asymmetric or uneven. In practice the bandwidth from the provider to the user (downstream) will be the higher speed path.

c) USES OF DSL

Firstly the existing telephone can be used. The telephone and the Internet are connected at the same time on a single phone line. Secondly connection to the Internet is much faster.

It enables:
• Faster downloads of digital information
• CD-quality audio
• Graphics-rich web sites
• Faster and better multimedia
• High-speed multi-player games
• View movies online

Thirdly ensures continuous connection to the Internet without the need to dial up the Internet provider and log on and off. The user has the option to install a web server and host a web site.

d) FUTURE OF DSL

Initially DSL was developed as an alternative to cable TV and video transmission to the home. This technology is not yet available to users but is a strong future possibility.

DSL also has the potential to evolve to Voice over DSL (VoDSL) which in addition to data service will have the ability to provide multiple normal telephone connections utilizing VoIP technology. This normal telephone connection will utilize part of the DSL bandwidth and will have the scope to conduct multiple telephone calls at the same time.