ADSL vs ADSL2
ADSL stands for Asymmetric Digital Subscriber Line; it is broadband technology that allows the simultaneous usage of the standard telephone handset as well as staying connected to the Internet. This is achieved by smartly managing the bandwidth available from the 2-wire pair used in telephone systems. As you would probably have already guessed from their names alone, ADSL2 is an improved version of ADSL. The biggest difference between them is the improved maximum speed that you can get with ADSL2, which can reach up to 12Mbps while ADSL can only reach 8Mbps.
Another key advantage that ADSL2 has over ADSL is the improved distance that ADSL2 can cover using the same copper wires. Improved range means greater area covered with the same number of junction boxes. The greater distance covered with ADSL2 would also translate to better transmission rates, at a given distance, as the rates vary with distance with maximum speeds only obtainable within close proximity to the exchange. Resistance to noise has also been improved in ADSL2. It may not have any effect under ideal circumstances but it allows for better and more reliable connections even when the conditions outside are less than ideal. This does not really
Just like most other upgraded technologies, ADSL2 is backwards compatible with ADSL. This means that all ADSL2 equipment is able to work at ADSL specs. This is good since it makes for an easier upgrade from ADSL to ADSL2. But not all routers and modems support ADSL2, so you need to make sure that yours does if your service provider decides to upgrade to ADSL2. But even if you have an ADSL2 capable modem, you would still be limited to what your service provider decides to utilize.
Aside from ADSL and ADSL2, there is also ADSL+. This second upgrade to ADSL provides much faster speeds compared to both ADSL and ADSL2. But just the same, the choice of which standard to use is still pretty much dependent on your ISP and the only thing that you can do on your side is to make sure that your hardware is able to handle any of the three standards mentioned above.
Summary:
1. ADSL2 is an improved version of ADSL
2. ADSL2 provides higher data rates compared to ADSL
3. ADSL2 has a longer reach compared to ADSL
4. ADSL2 is better at resisting noise compared to ADSL
5. ADSL2 equipment is backwards compatible with ADSL