Networking Basics - What is DSL and How Can it Benefit My Home or Small Business?
DSL or xDSL is a group of technologies that provide digital data transfer over
the telephone network. DSL originally stood for digital subscriber loop, but is
now commonly referred to as digital subscriber line. The typical transfer speeds
of DSL services range from 128 kilobits per second to 24,000 kbit/s.
DSL technology was originally begun as a part of the Integrated Services Digital
Network (ISDN). ISDN is a series of protocals designed implemented to allow for
digital transmission of voice and data over the telephone networks standard copper
wires. This resulted in better speeds and quality than the old analog system.
Most Common Forms of DSL
Asymmetric Digital Subscriber Line (ADSL) is a form of DSL that enables faster
transmission of data over these same copper wires than a standard dial up modem
can. It accomplishes this by using the frequencies that are normally not used by
a voice telephone call, in particular, frequencies higher than normal human hearing.
The drawback to ADSL is that it is ony effective over relatively short
distances. The user must be within 5 km of the telephone companies Central
Office. Once there, the ADSL signal is stripped off and immediately routed onto
a conventional internet network, while any voice-frequency signal is switched
into the conventional phone network. This is allows a single phone line to be
used for both voice and data transfer.
The most distinguishing characteristic of ADSL is that data transmission speeds
are greater in one direction than the other. This is often marketed to small
businesses or residential users who are most interested in accessing the
internet at an affordable price. It allows for higher download speeds, thus
decreasing the users time to view websites and download files. This is not
recommended if one has a need to upload large quantities of information or run
servers that would require large amounts of bandwidth in the other direction.
Symmetric Digital Subscriber Line (SDSL) is a DSL variant that enables the user
to have the same data transfer rate in both directions. This technology has a
transfer speed range of 72 to 2320 kbit/s. The primary drawback is that you must
be even closer to the telephone companies central office. A maximum distance of
3 km is all that is supported. It is also much more expensive.
Typical DSL technologies include:
High Data Rate Digital Subscriber Line (HDSL), the first DSL technology that
uses the higher frequency spectrum to transmit data.
Symmetric Digital Subscriber Line (SDSL), a standardized version of HDSL.
Asymmetric Digital Subscriber Line (ADSL), a version of DSL with a slower upload speed.