(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.