An ITU-T standard protocol for modems transmitting at 9600 bits per second with fall back to 4800 bps. V.32bis extended this to 14400 bps.V32 and V.32bis acheive bidirectional data transmission not by having different sets of tones at each end but by subtracting what is sent from what is received.
Last updated: 2004-07-30
V.25 bis ♦ V.27 ter ♦ V.28 ♦ V.29 ♦ V.32 ♦ V.32bis ♦ V.32ter ♦ V.34 ♦ V.35 ♦ V.42
Try this search on Wikipedia, Wiktionary, Google, OneLook.