Internet Connection Types - DSL Modem

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The DSL modem uses normal telephone lines to communicate to the ISP. However, instead of converting the digital signal to analog, the DSL modem sends a digital signal directly across the telephone line. The telephone line carries both the analog voice signal and the digital signal on the same wires to the telephone provider, which in turn must separate the two signals, connecting the digital signal to its servers and the analog signal to the appropriate telephone exchange equipment.

Your telephone provider must have the proper equipment installed to be able to provide DSL service to your location. Not all areas are converted to support DSL connectivity. Check with your telephone provider to determine whether they support DSL modems in your area.

Three basic types of digital modems can be used on a digital telephone line:

Integrated services digital network (ISDN): The ISDN modem is the oldest technology and is the most sensitive to distance. It offers up to 128 kbps of connectivity speed (more than double the speed of a dial-up modem), provided that the end connection is within 3.4 miles of the telephone exchange equipment. Performance degrades the farther away you are from the telephone exchange, which is one reason why ISDN didn’t catch on all that well.

Symmetric digital subscriber line (SDSL): SDSL provides a constant upload and download speed using the entire bandwidth provided on the telephone line, so it’s not able to share the same line with an analog signal. SDSL lines can provide up to 2,320 kbps of upload and download speeds.

Asymmetric digital subscriber line (ADSL): ADSL provides a constant upload and download speed but can share the same telephone line with an analog signal, allowing an ADSL modem and a telephone to operate at the same time on the single telephone line. ADSL splits the upload and download speeds, so they don’t have to be the same. This method allows much faster download speeds but at the expense of the upload speeds. ADSL lines can provide download speeds up to 24 megabits per second (Mbps) but usually limit upload speeds to no more than 3.5 Mbps. A typical home ADSL installation provides 8 Mbps of download speed and 1 Mbps of upload speed. For the average home user who downloads videos, music, and Linux distribution ISO files, ADSL is a perfect solution.

The second and third categories of digital modem Internet access is referred to as xDSL. Most xDSL providers distribute a simple DSL modem, which you install by simply plugging it into your normal telephone jack to connect to the telephone company. The DSL modem is usually set to communicate automatically with the telephone system’s ISP.

The DSL modem uses Ethernet to communicate with the workstation. The Ethernet protocol has been a communications standard for decades and is supported by various types of media. The two most popular methods for communicating via Ethernet today are
• Wired Ethernet network cards
• Wireless Ethernet cards

Source of Information : Wiley Ubuntu Linux Secrets

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