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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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