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Stands for "Digital Subscriber Line." DSL is a communications medium used to transfer digital signals over standard telephone lines. Along with cable Internet, DSL is one of the most popular ways ISPs provide broadband Internet access.

When you make a telephone call using a landline, the voice signal is transmitted using low frequencies from 0 Hz to 4 kHz. This range, called the "voiceband," only uses a small part of the frequency range supported by copper phone lines. Therefore, DSL makes use of the higher frequencies to transmit digital signals, in the range of 25 kHz to 1.5 MHz. While these frequencies are higher than the highest audible frequency (20 kHz), then can still cause interference during phone conversations. Therefore, DSL filters or splitters are used to make sure the high frequencies do not interfere with phone calls.

Symmetric DSL (SDSL) splits the upstream and downstream frequencies evenly, providing equal speeds for both sending and receiving data. However, since most users download more data than they upload, ISPs typically offer asymmetric DSL (ADSL) service. ADSL provides a wider frequency range for downstream transfers, which offers several times faster downstream speeds. For example, an SDSL connection may provide 2 Mbps upstream and downstream, while an ASDL connection may offer 20 Mbps downstream and 1.5 Mbps upstream.

In order to access the Internet using DSL, you must connect to a DSL Internet service provider (ISP). The ISP will provide you with a DSL modem, which you can connect to either a router or a computer. Some DSL modems now have built-in wireless routers, which allows you to connect to your DSL modem via Wi-Fi. A DSL kit may also include a splitter and filters that you can connect to landline phones.

NOTE: Since DSL signals have a limited range, you must live within a specific distance of an ISP in order to be eligible for DSL Internet service. While most urban locations now have access to DSL, it is not available in many rural areas.

Updated: September 25, 2014

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