What Is a DSL Modem?

A digital subscriber, or DSL line, is a type of high-speed Internet technology that transmits digital data via a regular local telephone network. A DSL modem is a hardware component that is designed to connect a computer or a router to a DSL Internet connection. The acronym DSL originally stood for "digital subscriber loop," but was later replaced with a more user-friendly term: digital subscriber line.

Function

DSL technology is made possible by the fact that a normal telephone line (or the plain old telephone service -- POTS -- as it is called) is made up of two copper wires to carry voice calls, in the form of analog data. However, the two lines have the capacity to transmit even more than just phone conversations. DSL modem technology is designed to take advantage of this extra capacity to transmit digital data.

A DSL modem works by dividing the frequencies in a single phone line into two sections that are called "bands," one with a high frequency that is at or above 25 kilohertz, and the other with a low-frequency at only 4 kilohertz or below. Digital data will be transmitted over the high-frequency band, while voice transmissions are carried over the low-frequency band.

Benefits

A key difference between a DSL modem and dial-up ISP modem is that a digital subscriber line can share the same phone line as a standard telephone. It allows for the telephone line to be used for calls, even as the user is connected to the Internet. DSL also offers far faster speeds than dial-up with a regular modem. Another key benefit offered by DSL technology is the fact that it requires little more than a DSL modem and an existing phone line. Often, the Internet service provider even includes the modem as part of its service.

Types

DSL modem speed may vary according to the DSL technology, line conditions and service level. There are two types of DSL technology: asymmetric digital subscriber line (ASDSL) and symmetric digital subscriber line (SDSL). ADSL is used most often by homes and small businesses. The typical download speed of a consumer DSL service ranges from 256 kilobits per second to 24,000 kilobits per second. On an ASDSL line, the upload speed will be lower than the download speed. On an SDSL, the upload speed will equal the download speed.

Features

When a DSL modem is installed in your home, a DSL filter will also be installed on each of your phone lines. The DSL filter will filter out the high frequencies from the phone line for transmitting for digital data, while reserving the lower frequencies for your phone to transmit the human voice. It is this feature that makes it possible to for the plain old telephone service to be used for Internet access and telephone service at the same time.

Significance

A DSL modem is one of two essential components of DSL equipment; the other is, a DSL access multiplexer, also referred to as a DSLAM. Like other modems, a DSL modem is basically a transceiver that is connected to your computer via an ethernet or USB cable and which transmits data from your PC to the DSL line. The DSLAM, located at the ISP's facilities, provides a connection between the customers' individual modems and the Internet.