Ruben Brito Maxim Liberman Drew Merrill

[attachment=18133]

Introduction
Asymmetric Digital Subscriber Line (ADSL) is a relatively new technology
promising to provide Internet access with data rates faster than a conventional 56K
modem. In addition to high data rates, it also provides the ability for a customer to both
have Internet access and talk on the phone at the same time. This technology has
tremendous potential; however, currently there is a major drawback. Based upon several
factors, the current range for ADSL service is a two to three mile radius from the
telephone company’s central office, which severely limits the number of customers. If
the range of service for this technology were to be increased, then there would be an
increase in the number of customers.



Background
Asymmetric digital subscriber line or ADSL is a technology that lets Internet
users take advantage of the Internet over current telephone lines. The current telephone
network provides each household with copper twisted cable that usually measures 24 or

26 AWG. Currently these cables are used primarily for voice communication. The
purpose of using ADSL technology is to utilize the higher frequency over these current
lines to transmit data.



The ADSL Frequency
Voice communication that is offered by the plain old telephone service (POTS)
operates below 4KHz. Since POTS does not utilize frequencies higher than 4KHz it
makes it ideal to use higher frequencies to transmit Internet data. One of the most
important concerns is to maintain voice communication aspect that the lines were original
intended for. Figure 1 (below) shows the frequency spectrum that ADSL utilizes. ADSL
starts at 30 KHz, which provides 26Khz between the start of ADSL and end of voice
communications. Having a band with such a leeway will assure that there will not be
interference to the current voice communication technology.


Workings of ADSL
The principle of ADSL is very simple; send coded data at a certain frequency.
There are, however, many problems that arise in trying to send so much information at
fast speeds. The process that used to send this data is called Discrete Multi-Tone or
DMT. DMT are transmitted over phone lines in frequency bands known as bins