The wide spread use of Internet and specially the
World Wide Web (WWW) have opened a need for greater bandwidth network
services that can be brought directly to subscriber's homes. These
services will provide the required bandwidth to surf the Web at fast
speed and the use of new technologies become simpler such as video
conferencing and video on demand (VoD). The DSL (Digital Subscriber
Line) service is now coming to Pakistan and is be available at Karachi
and would be available in near future in the bigger cities of country.
One of this technology is ADSL (Asymmetric Digital Subscriber Line)
which is working on existing telephone lines and promises download speed
around 8Mbps and upload speed of 640Kbps.
Unlike its acronym it doesn't really refer to a line,
but the modem that convert a line into a high-speed digital pipe. The
modem technology converts the copper twisted-pair telephone lines in the
existing telephony system just before it enters your home, into access
paths for multimedia and high-speed communication. It works over regular
phone lines that are already present and provide a high-speed access to
the Internet and remote networks. ADSL transmits more than 6Mbps
downstream (to the customer) and up to 640 Kbps upstream, depending upon
line length and the modem capabilities.
It is called asymmetric which means that it is faster
in one way than the other, there are two speeds to consider: down stream
(from the backbone to your computer) and upstream (from your computer to
ADSL can transmit more than 6Mbps to subscriber —
enough to provide Internet access, Video on demand, and LAN access. The
maximum upload speed could top out at 640Kbps, significantly slower than
down load speed.
This translate the download speed that are 140 times
higher than then the fastest analog modems plus the same line is also
available for making and receiving the phone calls at the same time.
Other members of xDSL family are HDSL( High date rate
DSL), SDSL (Symmetric DSL), and VDSL (Very high data rate DSL). All work
on the same principle but provide different speeds and used for
HOW ADSL WORKS
The twisted pair copper wire actually supports over
1MHZ of frequency Bandwidth. From these PSTNs (Public Switched Telephone
Networks) only utilizes 0 to 4 kHz of frequency Bandwidth because the
human hearing is limited to small range of sound frequencies
ADSL works by splitting the phone line into two
frequency ranges. The frequency below 4KHZ is reversed for voice and
range above is used for data. The figure 1 shows the frequency
distribution of ADSL. ADSL modem Squeeze up to 99% more capacity out of
phone line without interfering with regular phone services. This means
user could simultaneously talking on the phone or sending a Fax while
surfing the Internet.
For getting the ADSL connection, the customer is
provided with ADSL modem, a Splitter and a network card for their
Personal Computer. The Splitter is a low pass filter splitting the phone
line into two frequency ranges. Low frequencies are reserved for regular
telephone calls (voice), while higher frequencies are used for Internet
(data), making it possible to use the phone line for both telephone
calls and for Internet access.
Key Features of ADSL
Speeds ranging from 64 Kbps to 8 Mbps on your existing phone line.
connection to the Internet is always on
Connection is highly reliability
Unlimited downloads on a flat, monthly rate.
APPLICATIONS ON ADSL
Many target applications for ADSL are asymmetric
demanding high data rate downstream, to the subscriber, but relatively
low data rates demands upstream
Videos on Demand.
Movies on Demand.
Here at Pakistan Mutinet (www.multi.net.pk) has
started DSL service in the some parts of Karachi. Its DSL Broadband
shared service from Rs. 7,500/ month for 128Kbps (ADSL/SDSL), 256Kbps (ADSL/SDSL)
Rs.14,000/month and Rs. 26,000/month for 512 Kbps (ADSL/SDSL).
time installation cost RS 5,000/-
Customer is required to purchase a DSL Modem
Estimated cost for the DSL Modem is RS 9,000/-
The author is Assistant
Professor, Faculty of Information Technology IBA-Sukkur