High speed Internet over existing telephone lines


By Zahid.H.Khand
Sep 30 - Oct 06, 2002



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 the backbone).

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 different applications.


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.


Many target applications for ADSL are asymmetric demanding high data rate downstream, to the subscriber, but relatively low data rates demands upstream

* Video conferencing.
* Videos on Demand.
* Movies on Demand.
* Distance Learning.
* Internet Games


Here at Pakistan Mutinet ( 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).


* One 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