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offers high-speed Net access over existing copper wire. Here’s
a peak into DSL and its varients. by Mahesh Rathod
Subscriber Line is a technology that works on the presumption
that digital data does not require change into the analog
form and back
phone services (also called as POTS or Plain Old Telephone
Lines) are meant to carry analog voice signals over copper
wires. To transmit anything other than voice, for instance
data, and receive the same on your computer, this analog signal
has to be converted into digital information. This task is
done by the modem, which demodulates the analog signal into
digital data. This conversion from analog to digital and back
to analog limits the amount of data that can actually be sent
or received to 56 Kbps.
DSL (Digital Subscriber Line) is a technology that over comes
this bandwidth bottleneck. Additionally, it also provides
an always on, fast Internet access.
Fast Net access
DSL works on the presumption that digital data does not
require change into analog form and back. Digital data is
transmitted to your computer directly in its original form.
This allows the phone company to use a much wider bandwidth
for transmitting it to you. Also, if you choose, the signal
can be separated so that some of the bandwidth is used to
transmit an analog signal while the remaining can be used
to transmit a digital signal. This enables you to chat over
the telephone or access the Internet at the same time.
DSL provides secure, reliable high-speed Internet access to
homes and offices using high-bandwidth over ordinary copper
telephone lines. It is commonly referred to as xDSL due to
the different variations such as ADSL, HDSL, RADSL, etc, based
on upload/download speeds offered. Assuming your home or small
business is close enough to a telephone company central office
that offers DSL service, you may soon be able to receive data
at rates up to 6.1 Mbps (of a theoretical 8.448 megabits per
second), enabling continuous transmission of motion video,
audio, and even 3-D effects. More typically,
individual connections will provide from 1.544 Mbps to 512
Kbps downstream and about 128 Kbps upstream. A DSL line can
carry both data and voice signals and the data part of the
line always stays connected to the Internet.
With DSL technology, digital data does not require change
into analog form and back. It can be transmitted to your computer
directly as digital data and this allows for the use of a
much wider bandwidth. This means you can blaze down the information
highway with virtually no roadblocks.
How it works?
The several variants of DSL technology use the ordinary,
pre-existing copper telephone lines to
deliver high-speed data service to users. DSL services can
operate over the same pair of wires as an existing POTS phone
connection. At the customer's end, a splitter box separates
the DSL and POTS phone signals. Telephones, fax machines,
and other devices attach to the POTS phone line as usual.
The DSL splitter connects to a DSL modem, which in turn connects
to the user's PC via an Ethernet connection.
At the phone company's central office, a device called a DSL
Access Module (DSLAM) separates the phone signal and connects
it to the normal switched telephone network. The DSLAM also
acts as a router. Typically, the router connects to an Internet
backbone connection to provide Internet access for DSL users.
In some areas, the phone company can route one DSL user directly
to another. This allows the DSL connection to be used for
remote LAN access.
Despite its many positive
attributes, DSL is not entirely flawless. For instance,
in order to be eligible for DSL, the end user must be geographically
within a certain distance from the central telephone office,
otherwise the signal degradation is too great and DSL is unfeasible
(for ADSL that distance is two miles). In addition, numerous
standards still exist for DSL, hardware is still comparatively
pricey, and service is available only in limited areas.
Regardless of these drawbacks, DSL is still a quicker alternative
to analog modems and ISDN.
The introduction of DSL has fostered a fast growing and meaningful
competition in data services, most notably for Internet access.
In most major markets today, residences and small to medium-sized
businesses (SMBs) have the ability to order DSL service that
turns an ordinary copper local loop into a high-speed data
pipe for personal or shared use, at a fraction of the cost
of a traditional leased line.
In its multiple form DSL offer users a choice of speeds
ranging from 32 Kbps to more than 50 Mbps. These digital services
can be used to deliver bandwidth-intensive applications like
video-on-demand and distant learning. Today DSL is putting
high-speed Internet access within the reach of homes, small
and medium-size businesses. DSL takes existing voice cables
and turns them into a high-speed digital link. Over any given
link, the maximum DSL speed is determined by the distance
between the customer site and the telephone exchange.
There are several forms of xDSL, each designed around specific
goals and needs of the marketplace. Some forms of xDSL are
proprietary, some are simply theoretical models and some are
widely used standards. They may best be categorized within
the modulation methods used to encode data. See table for
a brief summary of some of the popular xDSL technologies.
Rathod can be reached at firstname.lastname@example.org