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Digital Subscriber Line, DSL

Image Caption: Schematic showing how DSL works. Credit: Jhbdel/Wikipedia (CC BY-SA 3.0)

The term DSL or ADSL (a higher speed connection) is the technology of delivering an Internet connection over wires using a local telephone network. A filter is used to block high frequency interference, enabling the user to have access to the Internet as well as use of the phone simultaneously. The rate of data transfer usually ranges from 256 kbps to 40 Mbps downstream (to the customer) and the data transfer is usually lower upstream (from the customer). To get equal transfer rates, a symmetric digital subscriber line (SDSL) is to be used.

In 1979 an early patent was filed for use of existing telephone wires to connect to data terminals of a remote computer. Bellcore developed the ADSL technology and filed for a patent in 1988 for placing wide-band digital signals along telephone company lines. Early DSL service required a dry loop connection, but later, the FCC required the lease of the lines to competing DSL carriers. This allowed the user to subscribe to two different services from two different providers on one line. For example: a telephone service and a DSL service from two different companies.

Early DSL data transfer was 8 Mbps over a 1.2 mile range, but a distance that was over 1.2 miles, the bandwidth was significantly reduced. So to increase the data transfer rate, ADSL loop extenders were added allowing higher DSL speeds at any distance. By 2012 there was a steady decline of DSL subscribers.

Telephones use a local loop (a pair of wires) for a connection with a frequency range of 300 – 400 Hertz. However, the wires themselves are capable of carrying a much higher range. The DSL takes advantage of the unused frequencies to transfer the data. To gain faster, the data is split into two different frequencies, one for upstream, and one for downstream traffic.

The two main pieces of equipment are a DSL modem on the users end, and a Digital Subscriber Line Access Multiplexer (DSLAM). The DSL connection is transmitted over existing cables reducing the cost of installing new lines. The DSL connection can only use one modem, to connect multiple users to the same DSL connection, a router is used with an Ethernet, powerline, or wireless network at the customer’s locality.

A naked DSL connection is one where the customer has DSL service without telephone service.

The demand for naked DSL service has expanded and the availability of the service has also grown.

The typical set up for a DSL connection starts with a DSLAM located at the telephone company’s central office which is connected to the phone lines. The phone line is then connected to the users DSL modem through a filter, then connected to a router (if applicable). Then from the router, the computer(s) and or laptop is connected by Ethernet or wireless.

Digital Subscriber Line DSL


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