What is the difference between ADSL and SDSL?

ADSL is known to be a type of DSL line. The main difference of this with the DSL is that the download speeds are going to be much higher as compared to the DSL. If you would look at the type of line that is being used in a lot of residential areas, this is the one that you can expect.
If you would look at the type of DSL line that is used in some commercial establishments, then you can expect that this may be the type of line that you will see. SDSL is also more expensive as compared to ADSL, probably because its download speed is also going to be even faster.