Digital Subscriber Line (DSL)
What IS DSL and how it Works

DSL (Digital Subscriber Line) is a technology for bringing high-bandwidth information to homes and small businesses over ordinary copper telephone lines. xDSL refers to different variations of DSL, such as ADSL, HDSL, and RADSL. If your home or small business is close enough to a telephone company office that offers DSL service, you may be able to receive data at rates up to 6.1 megabits per second. With it you can have continuous transmission of motion video, audio, and even 3-D effects. A DSL line can carry both data and voice signals and the data part of the line is continuously connected. DSL installations began in 1998 and will continue at a greatly increased pace through the next decade in a number of communities worldwide. DSL is expected to replace ISDN in many areas and to compete with the cable modem in bringing multimedia and 3-D to homes and small businesses.

How It Works
Traditional phone service connects your home or business to a telephone company office (like DoT or MTNL). The connection is over copper wires that are wound around each other and called twisted pair. The type of signal used for this kind of transmission is called an analog signal. An input device such as a phone takes an acoustic signal and converts it into an electrical equivalent in terms of volume and pitch. The telephone company's signaling is already present for this analog transmission. Hence it's easier to use that to get information to and fro between your telephone and the telephone company.

Your computer has to have a modem to modulate/demodulate the analog signal. It then converts to a string of 0 and 1 values called digital information. Analog transmission only uses a small portion of the available amount of information that could be transmitted over copper wires. Thus, the maximum amount of data that you can receive using ordinary modems is about 56 Kbps. With ISDN, you can receive up to 128 Kbps. The ability of your computer to receive information is constrained. This is because the telephone company filters the digital data, puts it into analog form and your modem has to change it back into digital.

In other words, the analog transmission between your home or business and the phone company is a bandwidth bottleneck. Digital Subscriber Line is a technology with which digital data does not require to be changed into analog form and back. Digital data is transmitted to your computer directly as digital data and this allows the phone company to use a much wider bandwidth for transmitting it to you. Also, if you choose to do so, the signal can be separated so that some of the bandwidth is used to transmit an analog signal. This would allow you to use your telephone and computer on the same line and at the same time.