V.22
V.22 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 that are transmitted with phase modulation: "00" is 0 degrees, "01" is 90 degrees, "11" is 180 degrees and "10" is 270 degrees. This technique increases the transmission speed to 1,200 bit/s. Transmission is in duplex over the frequencies 1,200 Hz for the calling modem and 2,400 Hz for the answering modem.