NetHandbooks Glossary
Definitions for teachers by teachers


ASDL - The variation called ADSL (Asymmetric Digital Subscriber Line) is the form of DSL that will become most familiar to home and small business users. ADSL is called "asymmetric" because most of its two-way or duplex bandwidth is devoted to the downstream direction, sending data to the user. Only a small portion of bandwidth is available for upstream or user-interaction messages. However, most Internet and especially graphics- or multi-media intensive Web data need lots of downstream bandwidth, but user requests and responses are small and require little upstream bandwidth. Using ADSL, up to 6.1 megabits per second of data can be sent downstream and up to 640 Kbps upstream. The high downstream bandwidth means that your telephone line will be able to bring motion video, audio, and 3-D images to your computer or hooked-in TV set. In addition, a small portion of the downstream bandwidth can be devoted to voice rather data, and you can hold phone conversations without requiring a separate line.
Unlike a similar service over your cable TV line, using ADSL, you won't be competing for bandwidth with neighbors in your area. In many cases, your existing telephone lines will work with ADSL. In some areas, they may need upgrading.
How it affects me: (see DSL)
Selected Link: The ADSL Forum, the illustrated ADSL Tutorial

by Sue Cooper

Asymmetric Digital Subscriber Line

Asymmetric Digital Subscriber Line, or Asymmetric Digital Subscriber Loop.A digital subscriber line (DSL) technology in which the transmission of data from server to client is much faster than the transmission from client  to server.Whereas with HDSL (High-Speed Digital Subscriber Line), transmission is 784 kilobytes per second in both directions, with ADSL, the rate from client  to server is 640 kilobytes per second and from server to client can be up to 6 megabits per second.

Like ISDN, ADSL uses standard phone lines to deliver high-speed data communications. But while ISDN's transmission speed is limited to 64 kbps, ADSL technology can deliver upstream (from the user) speeds of 640 kbps and downstream (to the user) speeds of more than 6 mbps. Even better, ADSL uses the portion of a phone line's bandwidth not utilized by voice, allowing for simultaneous voice and data transmission.

This kind of connection is useful with applications such as interactive TV and Video on Demand, because the data  the server sends is much more than the data sent by the  client.


by Constanza Bacca & Pedro Willging

DSL, ADSL- The Digital Subscriber Line uses ordinary copper phone lines to carry both voice and data to your home.  This service is provided by phone companies.  The data part of the line provides a dedicated or continuous connection to the Internet, providing up to 3 Mbps.  One draw back to this is that you have to be within a certain distance to a telephone switching station to take advantage of this service.  Asymmetric Digital Subscriber Line is another way to receive continuous internet access but at a faster speed (1.5 to 9 Mbps, comparable to most school networks).  "Asymmetric" means that the phone company can send lots of data to you, but you can't send much to them which makes video and data transfers faster.

DSL diagram

Webopedia "SDSL"
Webopedia "ADSL"

by Mike Sennert

DSL, ADSL (Digital Subscriber Line, Asymmetric Digital Subscriber Line)- DSL allows data to move over regular copper twisted phone lines. This type of circuit tends to be faster than the regular phone lines used with a modem. This results because DSL offers more bandwidth over the traditional copper wiring. It also allows a user to have a 24/7 connection to the Internet, while still being able to send and receive phone calls. The DSL technologies do not use the entire bandwidth of the twisted pair so there is still room for the voice channel. DSL is very similar to the Leased Lines and ISDN, but is now becoming a more popular choice. The DSL lines are faster than ISDN and cost less than the leased lines. DSL should be able to handle speeds up to 6.1 Mbps. More commonly though, individual connections provide from 1.544 Mbps to 512 Kbps downstream and about 128 Kbps upstream. The drawback to a DSL is you must be within close proximity to a telephone company's central office that offers this service. DSL has four types. One type is the ADSL. The ADSL gives more bandwidth "downstream" from the central office to the customer site than the reverse. In theory, ADSL allows download speeds up to 9 Mbps and upload speeds of up to 640 Kbps. ADSL was designed to take advantage of the one way media of most multimedia communications where more bandwidth is needed to get information to the user and not the reverse. Overall, DSL and its various types will be competing with Cable Modems in offering customers the fastest travel of information. It argues that Cable Modems will begin to create bottlenecks as more and more neighbors join. On the contrary, DSL and ADSL will use your own copper telephone wires, and therefore, hope to eliminate the bottlenecks.

Related links to DSL and ADSL
What is DSL?
Everything DSL
What is ADSL?
Westell-A leading provider of ADSL communications

by Kristin Zage

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Last updated: 31 July 2000