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DSL (Digital Subscriber Line), also referred as xDSL (x stands for different DSL techniques), is a group of technologies that provide high-speed Internet access, by using the ordinary telephone lines. It converts the ordinary telephone line into a high-speed passage for digital audio, video and data. DSL technology is widely used for business and personal purpose. The technology is simple as the setup required for network already exists. It does not keep the telephone line busy as is the case in the Internet access used in the Dial-up connection. However, the speed depends on the distance between the Internet service provider and the user. More the distance, less will be the speed of the Internet access.

How does DSL work?

POTS (Plain Old Telephone Service) uses copper wired (twisted cable) network, for the exchange of voice information. It uses analog signal transmission and requires a very low bandwidth (0-3400Hz), thus a wide bandwidth remains unused. DSL uses this unused bandwidth to provide Internet service. In DSL technique, the unused high range of frequency is used for broadband Internet access and the low range is used for voice transmission. In this technique, there is no analog to digital and digital to analog conversion. Digital data is directly fed into the computer using the DSL modem, thus allowing a wider range of bandwidth to be used. Splitters are used to split the low and high frequency signals into two bands. Filters are installed in phones to avoid interference between the range of frequencies used for DSL and telephonic conversion.

Difference between DSL and other Internet Services

Types of DSL Techniques

There are basically two types of DSL techniques -
Asymmetric DSL: ADSL, RADSL, VDSL are types of Asymmetric DSL
Symmetric DSL: SDSL, HDSL, SHDSL are types of Symmetric DSL

In Asymmetric DSL the bandwidth allotted for upstream and downstream is unequal, whereas in Symmetric DSL, it's equal. Let us look into the concept of upstream and downstream to understand the broad uses of the technologies.
Downstream: Data transfer from the server to the user is called as downstream. For e.g. downloading a song from any website.
Upstream: Data transfer from the user to the server is called as upstream. For e.g. uploading an image to a website.

Difference between DSL Techniques

As we already know, ADSL is one type of DSL technique. To get a brief overview of the various DSL techniques, refer to the box given below.