ADSL2 is a standard for delivering internet connectivity through telephone connections. It is designed to work approximately twice as quickly as ADSL. This means speed of up to 24Mb/s for downloads and 3.5Mb/s for uploads are theoretically possible.
To break down some of the jargon, DSL stands for Digital Subscriber Line and refers to technology allowing a normal telephone line to carry internet data at the same time as voice calls. ADSL is the most common version of this technology. The A stands for "Asymmetrical" and refers to a set-up which allows a faster speed for downloading data than uploading it. Because most home users download much more data than they upload, ADSL is more efficient and thus more economically viable.
ADSL2 works on the same principles, but uses an advanced form of the technology to cope with faster speeds. It requires new equipment at both ends of the connection. This means that ADSL2 will only be available in an area once the local telephone exchange has been upgraded. Customers who want to use ADSL2 services will then need a new modem router. There is no need to make any changes to the phone line itself. Whether companies charge more for an ADSL2 service is up to them, though some analysts believe competition between providers will mean there is little room for price rises.
As well as offering faster speeds on a line, ADSL2 also makes it possible to use two phone lines for a single connection. This is known as using "bonded lines." Doing this will increase the speed available, though it won't necessarily double the speed.
As with standard ADSL, ADSL 2 is still affected by the distance between the customer and the local telephone exchange. This is because the signal degrades more the further it has to travel over copper lines. Customers who live further away from the exchange will usually get slower speeds. This is unlike fiber-optic connections such as that offered by some cable providers, where speed is not affected by the distance.
What speeds providers offer with ADSL2 will vary. In most cases, using it will double the capacity for downloading data, meaning providers will offer up to double the speeds of their ADSL service in the same area. Providers may also offer an increased upload speed, though some may not consider it worthwhile to do this. Because ADSL2 is an agreed standard, providers should not use the term for any service which has download speeds below 8Mb/s or upload speeds below 800Kb/s.