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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. |
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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. |
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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. |
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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.
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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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