DSL is the acronym for Digital Subscriber Line. DSL is also known as xDSL which is group of technologies that supplies digital data transmission over the wires of local telephone network. Initial DSL stood for digital subscriber loop but the term Digital Subscriber Line fast became accepted since the year 2009 for Asymmetric Digital Subscriber Line (ADSL) which is the most accepted version of consumer – ready DSL. DSL can be used with the telephone line and with regular telephone since it utilizes high frequency bands whereas regular telephone uses low frequency.
Customer DSL speed ranges from 384 kilobits per second to 20 megabit per second when downloading. This is however dependent on the conditions of the line, the service – level implementation as well as the DSL technology. Usually the speed to upload is lower that the speed when downloading for ADSL and equal to the download speed for the atypical Symmetric Digital Subscriber Line (SDSL).
Getting DSL to work requires the act of separating the frequencies utilized in a single phone line into two primary bands, the ISP and voice. The voice operates on the lower frequency band while the ISP data uses the high frequency band. Users would generally install a DSL filter on each phone outlet. A DSL filter is an analog low pass filter that is placed between analog devices -such as analog modems or telephones –and a POTS telephone line. This is done to prevent intrusion between such devices and a DSL service that is working on the same line. The DSL filter will sort the high frequencies from the phone line so that the phone transmits or receives only the lower frequencies. The user of the device would then hear the human voice. The normal telephone equipment and the DSL modem may be used concurrently on the line without any intrusion from each other that is if the filters are utilized for all devices only.
Like many other forms of communication DSL comes from a scientific paper entitled A Mathematical Theory of Communication by Claude Shannon in 1948. ADSL was created in 1988 by Telcordia Technologies’ employees who placed wideband digital signals over existing baseband analog voice signal transmitted between central offices, customers on conventional twisted pair cabling and the telephone company.
The United States telephone companies use DSL to compete with cable internet. The initial DSL service ran over a dedicated “dry loop” however when the FCC commissioned the current local exchange carriers to rent their lines to competing providers such as Earthlink, shared line DSL became widespread.
DSL tends to circumvent the voice–frequency band yet the non –linear parts in the phone would oftentimes produce perceptible intermodulation products and spoil the operation of the data modem.