What is difference between DSL and ADSL?

Question Asked : What is difference between DSL and ADSL? What type of connection is commonly used in India? (Question asked on my Youtube Page) 

Asymmetric digital subscriber line (ADSL) is a type of digital subscriber line (DSL) technology, a data communications technology that enables faster data transmission over copper telephone lines than a conventional voiceband modem can provide. ADSL differs from symmetric digital subscriber line (SDSL).

ADSL works by utilizing frequencies that are not used by a voice telephone call. A splitter or DSL filter allows a single telephone connection to be used for both ADSL service and voice calls at the same time. ADSL can generally only be distributed over short distances from the telephone exchange typically less than 4 kilometres, but has been known to exceed 8 kilometres if the originally laid wire gauge allows for further distribution.

At the telephone exchange the line generally terminates at a digital subscriber line access multiplexer (DSLAM) where another frequency splitter separates the voice band signal for conventional phone network. Data carried by the ADSL are typically routed over telephone company's data network and eventually reach a conventional Internet Protocol network.

Thus the upload signal is weakest at the noisiest part of the local loop, while the download signal is strongest at the noisiest part of the local loop.

ADSL is a type of DSL where the upstream and downstream speeds differ (hence the "asymmetric" part). There are many variations of DSL technology for different types of application (HDSL, SDSL, etc). 

ADSL

ADSL is a broadband connection technology which utilizes existing copper wired telephone networks. ADSL uses a wide range of frequencies over an existing telephone line to deliver much higher speeds than standard 56k modem (between 10 and 140 times faster). It is also possible to use your phone while online. 

DSL

DSL stands for Digital Subscriber Line. Generally if you have a DSL connection, you are getting it right from the phone company. DSL is more like the older 'modems' in that they do use the standard copper phone lines that are in your house. DSL requires that there be a special switch installed at your local phone company's main routing station. DSL also has a limitation of a 4 mile radius. One of the cool features of DSL is that you do not need to have a 'special' line installed - you can be surfing the internet and talking to someone on the phone all on the same line. This is because DSL uses a high frequency that does not affect the normal use of your phone. 

There are two commonly type of DSL, DSL (also known as SDSL) and ADSL. DSL or SDSL is the more expensive, but offers the most bandwidth. The S in SDSL stands for Symmetric or synchronous, which means that the bandwidth of both upstream (sending data) and downstream (receiving data) are the same speed. The actual speed you get depending upon the package you sign up for, and how far away from the switch you are. The most common speeds are 256k (256kilobits)/second and 1Mb (1megabit)/second. ADSL (Asynchronous Digital Subscriber Line) is the same as SDSL, but the upstream bandwidth is smaller than the downstream. This version of DSL is generally more affordable than SDSL. Common ADSL speeds are 256kb downstream - 96kb upstream, 1mb downstream - 256kb upstream.

DSL was developed and patented in 1988 by Bell Communications Research, Inc. The main advantages of DSL at the time were the speed it offered and the fact that, for the first time, it allowed people to use Internet and phone service at the same time. The main disadvantage was that the digital signal's strength decreased as distance from the provider's central office increased.

Although it uses the same wiring as previous technologies, DSL sends information digitally. This greatly increases the amount of information that can be sent at once. ADSL is the most common type of DSL connection. 

Note :

• The opposite of ADSL is SDSL, which stands for symmetrical digital subscriber line. 
• SDSL provides a high-speed data connection that gives equal priority to upload and download speed. 
• Other types of DSL include Internet protocol subscriber line, rate-adaptive digital subscriber line, Uni-DSL and Etherloop.

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