Modem Standards

The CCITT is the Comité Consultatif International Téléphonique et Télégraphique, a United Nations advisory committee for international communications systems.

V.17 CCITT standard for 14400 bps faxes

V.21 CCITT 300 bps (not same as Bell 103)

V.22 CCITT 1200 bps (not same as Bell 212A)

V.22bis CCITT standard modulation for 2400 bps

V.25 CCITT standard, automatic calling and answering equipment

V.27ter CCITT standard, 2400/4800 bps modems

V.29 CCITT standard half duplex 9600 bps for faxing

V.32 CCITT standard modulation for 9600 bps

V.32bis CCITT standard modulation for 14400 bps

V.34 CCITT standard modulation for 28800 bps with automatic fallback to 26400, 24000, 21600 etc under poor line conditions

V.42 CCITT error control, incorporates LAP-M (Link Access Procedure - Modem with automatic fallback to MNP2,3,4

V.42bis CCITT compression also known as BTLZ (requires V.42 to be active)

V.FC A proprietary 28800 bps protocol superseded by V.34

MNP2-4 Older, but widely used error control method. MNP4 sends blocks of data synchronously between modems with the start and stop bits left out, resulting in a 10-20% gain in throughput.

MNP5 Data compression used only with MNP4. Less efficient than v.42bis.

MNP10 A data compression protocol optimized for cellular telephony.

Do not confuse the modem carrier speeds above ( in bps, Bits Per Second) with the speed of your computer's COM port. The modem speed is also known as the DCE (Data Communications Equipment) rate, and the COM port speed is also known as the DTE (Data Terminal Equipment) rate. The DTE rate should always be at least as high as the DCE rate, and can be several times higher if data compression is expected to be encountered. Common DTE rates are 9600, 19200, 38400 and 57600 bps.

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V.17	CCITT standard for 14400 bps faxes
V.21	CCITT 300 bps (not same as Bell 103)
V.22	CCITT 1200 bps (not same as Bell 212A)
V.22bis	CCITT standard modulation for 2400 bps
V.25	CCITT standard, automatic calling and answering equipment
V.27ter	CCITT standard, 2400/4800 bps modems
V.29	CCITT standard half duplex 9600 bps for faxing
V.32	CCITT standard modulation for 9600 bps
V.32bis	CCITT standard modulation for 14400 bps
V.34	CCITT standard modulation for 28800 bps with automatic fallback to 26400, 24000, 21600 etc under poor line conditions
V.42	CCITT error control, incorporates LAP-M (Link Access Procedure - Modem with automatic fallback to MNP2,3,4
V.42bis	CCITT compression also known as BTLZ (requires V.42 to be active)
V.FC	A proprietary 28800 bps protocol superseded by V.34
MNP2-4	Older, but widely used error control method. MNP4 sends blocks of data synchronously between modems with the start and stop bits left out, resulting in a 10-20% gain in throughput.
MNP5	Data compression used only with MNP4. Less efficient than v.42bis.
MNP10	A data compression protocol optimized for cellular telephony.