text: What is V.22? - Definition from Techopedia
  What Does V.22 Mean?
  Techopedia Explains V.22
  V.22 is an ITU Telecommunications Standardization Sector recommendation used for full duplex communication between two analog dial-up modems using phrase-shift keying modulation at 600 baud to carry data at around 1,200 or 600 bits per second. V.22 is a variation of the Bell 212 A modulation format.
  V.22 is the first true world standard developed for half duplex communication at 1,200 bps and is used mainly in Europe and Japan. In the United States, the protocol is defined by the Bell 212 A. Modems that adhere to this standard and are used on generalized switched telephone networks (GSTN) and point-to-point circuits.
  V.22 is pronounced as v-dot-twenty-two.
  The main characteristic features of modems using the V.22 standard are:
  They enable duplex operation on two-wire GSTN and point-to-point leased circuits.
  They include test facilities and scramblers.
  They use frequency division for channel separation.
  The modems use differential phase shift modulation for every channel with synchronous line transmissions at 600 bauds.
  The V.22 recommendations provide three alternative configurations.
  A configuration that supports 1,200 bps synchronous and 600 bps synchronous transmission
  A configuration that supports 1,200 bps start-stop and 600 bps start-stop transmission
  A configuration that supports all of the above configurations
  Asynchronous mode selections are made during the handshake sequence and provide compatibility between the second and third configuration alternatives.
  Data streams to be transmitted are divided into groups of two consecutive bits. Every bit is encoded as a phase change relative to the phase of the preceding signal elements. The bits at the receiver side are encoded and then reassembled in the correct order. The left-hand digit of the bit stream is the one that occurs first in the data stream as it enters the modulator portion of the modem after it has left the scrambler.