V.22bis is a transmission standard for modems. The V.22 standard transmits the bits in combination of two as dibits with 600 bit/s. Each character represents two bits, which are transmitted with quadrature phase modulation, but rotated by 45°: Dibit "00" has a phase of 45°, "01" of 135°, "11" of 225°, and "10" of 315°.
In the V.22bis method, the transmission speed is 2,400 bit/s. The V.22bis duplex modem operates in the public telephone network and on two- wire telephone leased lines using the frequency separation method.