V.27ter is an ITU-T recommendation for a half-duplexmodem, allowing 2400 and 4800 bit/s (PSK modulation).
V.28 is an ITU-T recommendation defining the electrical characteristics for unbalanced double-current interchange circuits.
V.29 is an ITU-T recommendation for a modem, allowing 4.8kbit/s, 7.2kbit/s and 9.6kbit/s transfer modes (PSK and QAM modulations).
V.32 (11/88) is an ITU-T recommendation for a modem operating as full-duplex on a four-wire circuit, or half-duplex on a two-wire circuit, allowing bidirectional data transfer at either 9.6kbit/s or 4.8kbit/s at a symbol rate of 2,400 baud instead of the 600 baud of the V.22 standards.[2]
V.32bis (02/91) is an ITU-T recommendation for a modem, allowing up to 14.4kbit/s bidirectional data transfer. Other additional defined data transfer rates are 12.0kbit/s, 9.6kbit/s, 7.2kbit/s, and 4.8kbit/s.[3] The standard was extended by several modem manufacturers to allow bidirectional data transfer rates of 19.2kbit/s, but never ratified as a V.32ter standard. These non-ITU-T standard modems were often referred to as "V.32terbo" modems.[4]
V.33 is an ITU-T recommendation for a modem operating as full-duplex on a four-wire point-to-point leased line allowing bidirectional data transfer at either 14.4kbit/s.
V.34 (09/94) is an ITU-T recommendation (superseded) for a modem, allowing up to 28.8kbit/s bidirectional data transfer using TCMmodulation. Other additional defined data transfer rates are 24.0kbit/s and 19.2kbit/s as well as all the permitted V.32 and V.32bis rates. Additionally, V.34 modems employ shell mapping as shaping code to reduce the transmit power.[5]
V.34 (10/96) is an updated ITU-T recommendation for a modem, building on the V.34 standard but allowing up to 33.6kbit/s bidirectional data transfer. Other additional defined data transfer rates are 31.2kbit/s, as well as all the permitted V.34 rates. Modems implementing this standard were often marketed under the moniker V.34+.[6]
