DSL (Digital Subscriber Line), also referred as xDSL (x stands for different DSL technologies), 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 link for digital audio, video and data. DSL technology is widely used for business and personal purpose. The technology is simple to install as the required wiring 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), much less than the physiacl bandwidth of the wire. 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, as there would be in a dial-up modem. Instead, digital data is directly fed into the computer by the DSL modem.
DSL Filters, also called Splitters, are used at the users end of the phone line to split the phone line's bandwidth into a low and high frequency band, one for voice, one for data. A filter must be used for each device (or group of devices) that connects to the phone line - nothing must be connected directly to the line.
At the other end of the phone line, in the phone companies exchange, the line is connected to a Digital Subscriber Line Access Multiplexer (DSLAM), which acts as a DSL filter and modem to a large number of phone lines.
Types of DSL technologies:
There are two groups of DSL technologies:
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.
(Downstream: Data transfer from the server to the user is called downstream. For e.g. viewing a website.)
(Upstream: Data transfer from the user to the server is called upstream. For e.g. uploading an image to a website.)