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DSL
Digital Subscriber Line (DSL)
provides high-speed digital modem
technology over a conventional telephone
line.
DSL uses signal frequencies above
those used by voice or fax, so the DSL
signal does not interfere with telephone
conversations or faxes. When a DSL
filter is connected to your phone jack,
its function is to split the data
(Internet) traffic from voice (phone)
traffic, and route them separately.
Voice traffic (talking on the phone
and fax signals) goes to the phone or
the fax machine, while your data traffic
(surfing the Web, downloading large
files or photos) goes through the DSL
modem and then to your computer, thus
allowing you to use both at the same
time.
Digital Subscriber Line (DSL) gives
you broadband access over your existing
copper telephone wires. A DSL connection
to the Internet is a high-speed, ‘always
on’ (you don’t need to dial up your ISP
each time you want to connect)
connection that lets you use your
telephone lines for making and receiving
calls and for Internet access
simultaneously.
DSL is also known as xDSL, with the
‘x’ standing for various kinds of DSL
technologies. These technologies differ
in the connect speed and connection
DSL FLAVORS
ADSL Lite (or G.lite) This is a lower
speed version of ADSL and provides
downstream speeds of up to 1Mbps and
upstream speeds of 512 kbps, at a
distance of 18,000 feet from the service
provider’s premises. It is intended to
simplify DSL installation at the user’s
end.
R-ADSL The
Rate-Adaptive Digital Subscriber Line
provides the same transmission rates as
ADSL, but an R-ADSL modem can
dynamically adjust the speed of the
connection depending on the length and
quality of the line.
HDSL The High
Bit-Rate Digital Subscriber Line
provides a symmetric connection, that
is, upstream speeds and downstream
speeds are the same, and range from
1.544 Mbps to 2.048 Mbps at a distance
of 12,000–15,000 feet. Symmetric
connections are more useful in
applications like videoconferencing,
where data sent upstream is as heavy as
data sent downstream. HDSL-II, which
will provide the same transmission rates
but over a single copper-pair wire, is
also round the block.
IDSL The ISDN Digital Subscriber Line
provides up to 144 kbps transmission
speeds at a distance of 18,000 feet (can
be extended), and uses the same
techniques to transfer data as ISDN
lines. The advantage is that, unlike
ISDN, this is an ‘always on’ connection.
SDSL The Single-line
Digital Subscriber Line provides
symmetric transmissions at rates similar
to HDSL. The difference is that it uses
a single copper-pair wire to do so
(while HDSL uses two or three), and
operates at a maximum distance of 10,000
feet from the service provider’s
premises.
VDSL The Very High
Bit-rate Digital Subscriber Line is the
fastest of all xDSL flavors and provides
transmission rates of 13–52 Mbps
downstream and 1.5–2.3 Mbps upstream
over a single copper-pair wire, at a
distance of 1,000–4,500 feet from the
service provider’s premises.
The ADSL and HDSL are very common in
use, the former being more popular for
home usage.
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