Optimizing Bandwidth through Asymmetry Most Internet applications require uneven amounts of upstream and downstream bandwidth. In other words, users tend to move greater amounts of data in one direction than they do in the other direction. Generally speaking, Internet users access more information and receive more data than they transmit. That's the nature of the Internet. A user's upstream capacity is typically limited to sending commands or transmitting small data files to a server.
Much more information travels downstream.
ADSL was designed to take advantage of this trend in uneven bandwidth. For telephone companies, ADSL may be the key to overcoming the congestion created by explosive Internet growth. If telephone companies hope to capture the Internet data carrier market, they can't use equipment designed for short voice traffic. The average voice call lasts about three minutes. Telephony magazine reported as early as 1994 that nearly 20 percent of all on-line data service connections lasted more than an hour.