Dial-Up Modem Standards
The CCITT has classified dial-up modems according to modulation standards. Listed here are the standards and their different transmission speeds.
The CCITT, an international committee that specifies the way modems and fax machines transmit information to ensure compatibility among modems, has classified dial-up modems according to the following modulation standards:
- Bell 103M & 212A: Older standards, Bell 103 transmits at 300 bps at 300 baud and 212A transmits at 1200 bps at 600 baud.
V.21: Capable of only 300 bps, it is an international standard used mainly outside of the U.S.
- V.22: Capable of 1200 bps at 600 baud. Used mainly outside the U.S.
- V.22bis: Used in the U.S. and out, it is capable of 2400 bps at 600 baud.
- V.23: Used mainly in Europe, it allows the modem to send and receive data at the same time at 75 bps.
- V.29: A one-way (half-duplex) standard that is used mostly for fax machines. Capable of 9600 bps.
- V.32: A full-duplex standard capable of 9600 bps at 2400 baud. V.32 modems automatically adjust their transmission speeds based on the quality of the lines.
- V.32bis: A second version of V.32, it is capable of 14,400 bps. It will also fallback onto V.32 if the phone line is impaired.
- V.32ter: The third version of V.32, capable of 19,200 bps.
- V.34: Capable of 28,000 bps or fallback to 24,000 and 19,200. This standard is backwards compatible with V.32 and V.32bis.
- V.34bis: Capable of 33,600 bps or fallback to 31,200.
- V.42: Same transfer rate as V.34 but is more reliable because of error correction.
- V.42bis: A data compression protocol that can enable modems to achieve a data transfer rate of 34,000 bps.
- V.44: Allows for compression of Web pages at the ISP end and decompression by the V.44-compliant modem, so transmitting the same information requires fewer data packets.
- V.90: The fastest transmissions standard available for analog transmission, it is capable of 56,000 bps.
- V.92: Transmits at the same speed as V.90 but offers a reduced handshake time and an on-hold feature.
Note: CCITT was renamed to ITU-T in 1993, however modem standards are still called CCITT standards. The full list of ITU-T (V Series Standards) can be found here.
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