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Frequently Asked Questions about DSL
DSL is a very new technology to many people, and therefore there is quite a bit of confusion and misinformation concerning this exciting new carrier method. This FAQ document is devoted to answering some of the more common questions and concerns about DSL.
What is DSL?
DSL is an abbreviation for Digital Subscriber Line technology. DSL refers to the technology used between a customer's premises and the telephone company that enables more bandwidth over the already installed copper cabling than users have traditionally had. It is a distance-sensitive technology and available speeds depend on your location.
Why use DSL?
DSL is perfect for personal users and businesses looking for affordable, high-speed Internet access. It provides a connection 3 to 30 times faster than a 56k dial-up connection, allowing you to download files in a fraction of the time. DSL gives you instant Internet access 24-hours a day, 7-days a week. DSL is a dedicated connection and allows one computer, or many computers joined by a network to access the Internet simultaneously.
How does DSL work?
DSL utilizes more of the bandwidth on copper phone lines than what is currently used for plain old telephone service (POTS). By utilizing frequencies between 26kHz and 1MHz, DSL can encode more data to achieve higher data rates than would otherwise be possible in the restricted frequency range of a POTS network (only up to 4 kHz). In order to utilize the frequencies above the voice audio spectrum, special DSL equipment must be installed on both ends and the copper wire in between must be clean enough to sustain the higher frequencies for the entire route. This means that bandwidth limiting devices such as loading coils can prevent DSL from being used.
Why is DSL better than other broadband delivery methods?
DSL's main advantage lies in its means of deployment. DSL is deployed over standard twisted copper phone lines. This means that setup is very inexpensive compared to fiber optic cables and co-axial cable, which require physically digging up the ground to lay the cable. With DSL the infrastructure is already in place and ready to use.
What are the various types of DSL?
There are several competing forms of DSL, each adapted to specific needs in the marketplace. Some forms of DSL are proprietary, some are simply theoretical models and some are widely used standards. They may best be categorized within the modulation methods used to encode data. Below is a brief summary of known types of DSL technologies. These technologies are sometimes collectively referred to as xDSL.
Asymmetric Digital Subscriber Line or ADSL is the most popular form of DSL technology. The key to ADSL is that the upstream and downstream bandwidth is asymmetric, or uneven. In practice, the bandwidth from ISOMEDIA to the user (downstream) will be the higher speed path. This mainly due to the desire to accommodate the typical Internet usage pattern where the majority of data is being sent to the user (webpages, graphics, programs and video) with minimal upload capacity required (keystrokes and mouse clicks). Downstream speeds typically range from 256kbps to 8mbps. Upstream speeds typically range from 64kbps to 640kbps, and have a distance of approx. 18,000 circuit feet.
Symmetric Digital Subscriber Line or SDSL is a connection where data transfers at the same rate in both directions, or equal. Speeds typically range from 144kbps to 1.54mbps. The distances range from 1.54mbps at 6,000 circuit feet to 384kbps at 15,000 circuit feet.
The third and final competing form of DSL is IDSL, which is a DSL technology that uses ISDN technology. Speeds are limited to 144kbps bi-directionally and the circuit can be as long as 8 miles.
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