3am Systems - Wireline Modem V.xx Modulations

V.21 - Adopted in 1964, V.21 is a duplex split-band modem using frequency shift keying (FSK), supporting a maximum speed of 300 bps. It is designed to be simple enough to permit an implementation using passive (LC) filters.

V.22 - Adopted in 1980, V.22 is a duplex split-band modem using phase shift keying (PSK), supporting a maximum speed of 1200 bps. The transition from FSK to PSK makes better use of the available channel capacity, however, it also necessitates the use of a scrambler and more complex modulation/demodulation circuitry. Each channel uses a symbol rate of 600 baud, with each symbol having 4 states (0/90/180/270°). More...

V.22 bis - Adopted in 1984, V.22 bis improves upon V.22 by using quadrature amplitude modulation (QAM), supporting a maximum speed of 2400 bps. The transition from PSK to QAM necessitates the use of adaptive equalization and more complex signal processing. Each channel uses a symbol rate of 600 baud, with each symbol having 16 states (of combinations of phase and amplitude). More...

V.32 - Adopted in 1984, V.32 improves upon split-band modems, with the key innovation being echo cancellation. Echo cancellation provides channel separation without splitting the available bandwidth. While still using QAM, V.32 supports a maximum speed of 9600 bps. Each channel uses a carrier of 1800 Hz, and a symbol rate of 2400 baud, with each symbol having 16 states, or optionally, 32 states with Trellis coding. QAM with Trellis coding, also known as Trellis-coded modulation (TCM), is another key innovation that provides forward error correction (FEC) with coding gain, enabling a more effective use of the channel's capacity. More...

V.32 bis - Adopted in 1991, V.32 bis improves upon V.32 following further developments in signal processing electronics that make it possible to implement 'madly complex' modulation schemes. Using TCM, V.32bis supports a maximum speed of 14,400 bps. Each channel uses a carrier of 1800 Hz, and a symbol rate of 2400 baud, with each symbol having 128 states.

V.34 - Adopted in 1994, V.34 improves upon V.32 bis by using a range of carrier frequencies and symbol rates beyond 2400 baud, and a 1664-point super-constellation, with all symbols being a subset of this super-constellation. For example, at 28,800 bps, Fc=1800 Hz, Rs=3000 baud, Symbols=1408; at 33,600 bps, Fc=1959 Hz, Rs=3429 baud, Symbols=1664.

V.90 - Adopted in 1998, V.90 improves upon V.34 by using pulse-code modulation (PCM) for the downstream link, achieving speeds of up to 56,000 bps when connected to a digital modem, sending G.711 signals with a symbol rate of 8000 baud.

V.92 - Adopted in 1999, V.92 improves upon V.90 by adding 'Quick Connect', 'Modem on Hold', 'V.PCM upstream' and 'V.44 compression' features. More...