An example of a DSL internet link is SDSL. It uses copper telephone connections to transmit digital data, similar to ADSL. The definition of "symmetric" states that the capacity used for transfer and download is the same.

SDSL is better adapted to consumers who require a dependable data link to transmit and receive identical quantities of data because data moves at the same pace in both ways. For instance, a company that requires an Internet link for Telephony service will evenly use send and receive capacity.

The other DSL link type, called ADSL, is asymmetrical; users can send much more slowly than they can receive. Most Providers provided ADSL to their residential clients rather than SDSL because the majority of household Internet users receive more data than they send.