Internet: Hardware Student Papers: Lundrem - California Western
Internet: Hardware Student Papers: Lundrem

Asymmetric Digital Subscriber Line (ADSL)

by Natasha Lundrem

       ADSL stands for Asymmetric Digital Subscriber Line (ADSL) and is a faster alternative for accessing the Internet. The term refers to a set of two modems. One modem is located in the user's home or office and the other modem is located at the telephone company. The modems convert a standard, twisted-pair copper telephone line into a high-speed digital pipe. ADSL is faster than a 56 Kbps modem, faster than ISDN, and can be faster than a cable connection.

       ADSL employs the unused bandwidth in a telephone customer's existing copper telephone line. The larger bandwidth allows faster transport of data. The modems separate the copper telephone line into three channels. One channel is for a regular telephone line, for phone calls and faxes. The other two channels transport data upstream and downstream. The line is asymmetrical, meaning the information delivered downstream (to a home computer) travels faster than the information traveling upstream (away from the computer). The reason the streams travel at different rates is because typically more information is transmitted from the Internet (e.g. an entire web page) than is transmitted away (e.g. a click on an icon). Downstream transfer rates can vary from 640Kbps to 2MB. These transfer rates can also change with distance.

       Normal telephone usage only takes up about 1% of the phone line. The remaining 99% of the phone line can transmit information at a rate of 50 to 150 times faster than a 28.8 Kpbs modem using ADSL. ADSL technology takes advantage of unused capacity by dividing a copper telephone line into hundreds of segments, each of which is large enough to carry one telephone call.

       ADSL is perfect for receiving multimedia, audio, video, and animation files in real time. ADSL technology provides an Internet connection, which is both faster than conventional modems and permanent, because it does not interrupt the regular telephone service that phone consumers currently use.

       Now local telephone companies wanting to take advantage of the "information superhighway" have a cost-effective solution without investing in fiber-optic cable or other expensive infrastructure changes and without disturbing plain old telephone service (POTS).

       There are numerous advantages to having Internet access via the telephone company versus cable providers. ADSL is a dedicated connection between the user's home and the network whereas all cable subscribers share a cable modem service. This results in two major differences. First, ADSL does not get slower at busier times when the network experiences heavier use. Second, the network is more secure. In fact, if you were to transmit upstream on most TV cable presently installed, you would likely be broadcasting to your neighbors. Additionally, a user need not subscribe to cable either.

       ADSL is still a young technology but appears to be a viable solution. ADSL does not require new infrastructure and it has the convenience of speed and security while allowing the use of the telephone or fax while accessing the Internet.