two-binary, one-quaternary

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

two-binary, one-quaternary
2B1Q

   <communications> (2B1Q) A {physical layer} encoding used for
   {Integrated Services Digital Network} {basic rate interface}.
   2B1Q represents two {bits} (2B - a "dibit") using one of four
   signal levels (1Q - a "quadratude").  The first bit of the
   dibit is indicated by polarity: positive indicates a binary 1
   and negative indicates a 0.  The second half of the dibit is
   indicated by voltage magnitude: 1 Volt indicates a binary 1
   and 3 Volts indicates binary 0.

   (2003-01-10)