Symmetric digital subscriber line (
SDSL) refers to
digital subscriber line (DSL) technologies, that is, technologies for transmission of digital data over the copper wires of the telephone network where the
bandwidth in the
downstream direction, from the network to the subscriber, is identical to the bandwidth in the
upstream direction, from the subscriber to the network. This
symmetric bandwidth can be considered to be the opposite of the asymmetric bandwidth offered by
asymmetric digital subscriber line (ADSL) technologies, where the upstream bandwidth is lower than the downstream bandwidth. SDSL is generally marketed at business customers, while ADSL is marketed at private as well as business customers.