DSL stands for digital subscriber line. It allows higher bandwidths over the same conventional telephone lines that are used today. DSL is provided one of two ways--from your local phone company and from an ISP. Phone companies can provide the service, whereby they route DSL traffic to an ISP. This represents a broadband network, where the bandwidth of one individual DSL connection is shared among several customers (usually there is one repeater per household area that can serve 50-100 customers). The advantage is that the distance is not limited, but the bandwidth is (this is dependant upon how many customers are online at one time). If a dedicated DSL circuit is provided by an ISP, the distance to the cannot be more than 18,000 - 20,000 feet.  
  There are several variations in DSL technology, each with different bandwidth rates. SDSL stands for high-bitrate symmetric DSL. It's the oldest and most mature form of DSL, providing 128 KBps - 2.3 MBps rates. It's limited to a 20,000 feet distance.  
  ADSL (asymmetric DSL) provides a higher download bandwidth than the upload. With many companies, it is the only DSL service available. Download rates run anywhere from 256 KBps to 8 MBps, and upload rates run up to 1 MBps. However, to get 6 MBps or higher, the distance from the provider cannot be more than 9,000 feet. One variation sometimes mentioned is RADSL. It is the same as ADSL, except the provider will retest the lines every day and establish the highest possible bandwidth.  
  IDSL is simply a modified version of ISDN. Here, the connection is dedicated so that the price of the connection is not dependant upon how long the customer is connected to the internet. Existing ISDN equipment can be utilized if the customer switches to IDSL. IDSL runs at a maximum of 128 Kbps.

  VDSL is an emerging version of DSL, providing up to 52 MBps rates. The price paid for the increase in bandwidth is a greater limit in the distance from the provider. VDSL comes in both synchronous and asynchronous flavors. Asynchronously, the highest rates are 52 MBps downstream and 6.4 MBps upstream. Synchronously, the maximum rate is 34 MBps. With either connection type, the maximum distance alotted to get the maximum rate is 1,000 feet. The link must be fiber optic that terminates in an optical network termination unit (ONU). From there, the signal is delivered to the user over copper.  

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