Asymmetric Digital Subscriber Line (ADSL) is a new technology that is largely replacing ISDN where it is available

Comparison

ADSL is a broadband technology providing fast Internet access (amongst other applications) over existing telephone lines. It is far quicker than ISDN and is 'always on' (as long you are connected to the internet service provider).

You can use your existing telephones by fitting an ADSL filter to each one.

ADSL has a higher download speed than upload speed, hence the word 'Asymmetric'.   Another term for this is 'asynchronous'.

The most popular speed of service in the UK is 512Kbps, however if the line quality is good enough, there are now service providers offering up to 2Mbps

The main problem with ADSL is that you must be fairly close to an ADSL enabled exchange to use the service - 3.3Km to 5.5Km away depending on the quality of the line.

In October 2003 only about 81% of the population could access the service.

BT are now developing lower speed ADSL that can work a bit further away from the exchange. This means by 2005 they estimate 95% of the population will be able to access the service.