When two V.32 bis modems talk to each other at 14,400BPS (Bits Per Second)
they make 128 different possible sounds to each other. The sounds are various
combinations of phase shifts, and amplitude (loudness) levels of the basic carrier
tone. The modem changes the sound 2400 times a second
(hence 2400 baud). You could imagine a diagram of the possible sounds arrayed like a
lattice or trellis of intersections of phase and amplitude.