SDSL

from The Free On-line Dictionary of Computing (8 July 2008)

Single-line Digital Subscriber Line
SDSL
S-HDSL
Single-pair High Speed Digital Subscriber Line

   <communications, protocol> (SDSL, or Single-pair High Speed
   Digital Subscriber Line, S-HDSL) A form of {Digital Subscriber
   Line} similar to {HDSL} but providing {T1} or {E1} connections
   over a single {twisted-pair} copper line.

   (1998-05-18)