SDSL in IT Glossary

Short for symmetric digital subscriber line, a technology that allows
more data to be sent over existing copper telephone lines (POTS).
SDSL supports data rates up to 3 Mbps.
SDSL works by sending digital pulses in the high-frequency area of
telephone wires and can not operate simultaneously with voice
connections over the same wires.

SDSL requires a special SDSL modem. SDSL is called symmetric
because it supports the same data rates for upstream and
downstream traffic. A similar technology that supports
different data rates for upstream and downstream data
is called asymmetric digital subscriber line (ADSL).
ADSL is more popular in North America, whereas SDSL is
being developed primarily in Europe.

symmetric
having similarity in size, shape,
and relative position of corresponding parts.