Monday, August 24, 2009

DSL (Digital Subscriber Line)

What is DSL?

DSL, or Digital Subscriber Line, is a type of high speed Internet access. When deciding on which type of Internet access to get, you may have several options: dial up, DSL, cable, fiber optic, satellite, mesh wireless or point distribution wireless. However, in many geographic locations you may be limited in the types of Internet access that are available to you.

DSL Internet access is delivered across the telephone network backbone, an ordinary telephone connection jack can be used to plug in to DSL Internet access. Not all phone companies offer DSL service in every residential area, so even if phone service is available, it does not necessarily mean that DSL will also be available.

You can get DSL service from companies other than your local phone company, however, so even if the phone company doesn't provide DSL service, there may be other local companies who do.
As compared to a dialup connection, where a modem is used to connect to the Internet over the phone lines, DSL is always on. There is no need to dial in or disconnect. And DSL is generally much faster than a dialup connection which is limited to 56k.

DSL speed and bandwidth are usually somewhat lower than cable, which is available wherever cable TV service is available; however cable Internet access is a shared media. What this means is that if cable is available in your area, all users who are connected to the cable hub share a fixed amount of bandwidth. The more devices that are connected, the less bandwidth each user gets. With DSL, each user has a dedicated circuit and doesn't share bandwidth on that circuit with any other users.

Even though with DSL you don't have to share access with other users, the closer your home is located to a telephone company's central office switch, the better. This is a physical building where the local switching equipment is located. Distance to the switch is a determining factor for whether or not DSL service is available, and what speed will be available.

DSL service introduces interference on your phone line. It is necessary to eliminate this "noise" by using a filter supplied by your DSL provider.

The most common types of DSL for home connections are ADSL, SDSL, IDSL and RADSL.
ADSL is Asymmetric DSL

Download speeds are much faster than upload speeds. This is the most common type of DSL access for home connections.

SDSL is Symmetric DSL
Upload and download speeds are
virtually the same, or symmetric. This is a good connection for gaming or hosting a server and typically costs more than ADSL.

IDSL provides a maximum 144kb per second connection (which is slow) and it is based on ISDN technology which makes it available at farther distances from the central office switch. It also costs more than SDSL access.

RADSL is Rate Adaptive DSL
Speed on RADSL connections varies based on line conditions. In some situations this is the only DSL service available, but ADSL or SDSL would be preferable.

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