What is DSL and ADSL?

What is DSL

DSL (Digital Subscriber Line) is a technology for bringing high-bandwidth, high-speed Internet access to homes and businesses over ordinary copper telephone lines. A DSL line can simultaneously transmit data and voice signals, and provides an ‘always on’ connection to the Internet.

DSL achieves higher data transfer rates by using more of the available bandwidth spectrum, enabling continuous transmission of streaming video, audio and graphic-rich information.

xDSL refers to different variations of DSL, such as ADSL, HDSL, and RADSL.

What is ADSL?

ADSL (Asymmetric Digital Subscriber Line) is the most popular form of DSL for home users and Small to Medium Enterprises (SMEs).

ADSL is called "asymmetric" because most of its bandwidth is devoted to the downstream direction, i.e. sending data to the user. As most Internet use requires greater downstream bandwidth, only a small portion of bandwidth is available for upstream or user-interaction messages.

How fast is ADSL?

ADSL speed is up to 20 – 50 times faster than a conventional 56Kbps modem.

Downstream speeds typically range from 1.5Mbps to 9Mbps, and upstream speeds between 64Kbps to 1.5Mbps.

What quality can I expect from ADSL?

Like cable and satellite, ADSL will enable users to watch videos, listen to CD-quality music, conduct online video conferences in real time without experiencing delay and view graphic-rich images.

The quality of ADSL is affected the further away a user is from the closest telephone exchange, therefore it is not considered a practical solution for rural or remote areas.

However, as most Australian Internet users are within an optimal distance from an exchange (i.e. within 3 kms), ADSL is an effective, highly available and convenient option for high-speed Internet access.

How does ADSL work?

Traditional phone service (sometimes called "Plain Old Telephone Service" or POTS) connects users to a telephone exchange over copper wires that are wound around each other and called twisted pair. Telephone exchanges were created to transmit voice information with other phone users via an analogue signal. As analogue transmission only uses a small portion of the available amount of information that can be transmitted over copper wires, the maximum amount of data that can be received using an ordinary modem is about 56 Kbps. With DSL, the DSLAM (Digital Subscriber Line Access Multiplexer) at the exchange assumes digital data does not require change into analogue form and back, which results in a much wider bandwidth.

The line distance also determines the rate of data transmission, with speeds ranging from 1.5Mbits/second to 6.0Mbits/second downstream and from 16 Kbits/second to 800 Kbits/second upstream.

What are the benefits of ADSL?

ADSL offers users several benefits over other existing Internet access technologies, including:

- High-speed Internet access up to 20 – 50 times faster than conventional 56Kbps modems
- An ‘always on’ connection
- The ability to make and receive telephone calls while online
- Access to high-bandwidth data such as video, CD-quality audio, and graphic-rich web pages

Does ADSL require special hardware?

ADSL needs a few important hardware items for it to correctly work. In order to separate voice transmissions from data over the copper line, a splitter would be installed outside the user’s home or office. The user will also be provided with a special ADSL modem.