DSL internet access

DSL, or Digital Subscriber Line, is a set of technologies that allow computers to transfer data digitally across the wires in a phone network.

Originally developed in 1988, DSL could use standard phone lines to transfer data very quickly without interfering with voice communications.

DSL services started becoming widely available around the world in the late 1990s. In Australia they became popular in 2002 and have grown rapidly ever since.

The speed of DSL varies from 128kbps, about double the speed of modern dial-up modems, up to more than 50,000kbps (50Mbps) depending on the DSL technology and distance from a telephone exchange.

In Australia today, ADSL is widely used to deliver speeds between 256kbps and 1.5Mbps. Newer services using ADSL2+ now offer more than ten times this speed in certain areas.

To use a DSL service, households require an appropriate DSL modem and their phone line has to be configured to use the DSL service. The local telephone exchange has to be enabled for DSL. It is still an issue in some areas of Australia that certain exchanges are set up in ways that do not allow DSL to be rapidly introduced.

Because of the way DSL works, the shorter the wire from someone's home to a DSL-enabled telephone exchange, the better the performance. Homes further than a few kilometres from an exchange tend to receive slower DSL internet access speeds.

Types of DSL

ADSL

ADSL or Asynchronous Digital Subscriber Line is the most common form of DSL used in Australia and is available to many people across most cities and towns. It is described as asynchronous because the speed at which messages are received by ADSL modems are faster than the speed of those sent. For example a standard ADSL connection may be 256kbps into the home, but only 64kbps out of the home, or 256/64Kbps. Other common speeds include 512/128Kbps and 1Mb/256Kbps.

ADSL has a theoretical maximum speed of 8/1Mbps. However, in Australia Telstra limits the speed on its national phone network to 1.5Mbps to manage network performance and ensure a consistent speed for people further away from exchanges.

One of the fastest ADSL service offered in Australia is a 2Mbps/512Kbps from TransACT in the ACT. TransACT uses its own fibre-optic network to allow the faster speed.

ADSL 2

ADSL2 increased the maximum speed of ADSL to 12/3.5Mbps. However, it had a very short lifespan and has already been replaced by the much faster ADSL2+ standard.

ADSL 2+

ADSL 2+ provides internet connections up to 24/1Mbps. However, the maximum speed drops rapidly at greater distances from a local phone exchange. The technology is now being rolled out in Australia by a number of companies.

ADSL 2+ speeds allow the next level of broadband internet access, providing for the live viewing of full-screen video on PCs and similar high bandwidth services. It is already proving popular with one internet service provider, iinet , reporting in June 2006 that after two years of operation, the company had reached 100,000 ADSL2+ subscribers .

VDSL

Also known as Very-high-bit-rate DSL, VDSL is an extremely high speed DSL solution, but only operates at high speeds for very short distances.

Capable of up to around 52/3Mbps or 13/13Mbps speeds over a standard phone line, VDSL is used in TransACT's fibre-optic network to connect individual homes to the fibre-optic cables. These wires tend to be no longer than a few hundred metres long. VDSL is not in regular use elsewhere in Australia.