- Modem standards
The CCITT, an international committee that specifies the way
modem s andfax machines transmit information to ensure compatibility among modems, has classified dial-up modems according to the followingmodulation standards:* Bell 103M & 212A: Older standards, Bell 103 transmits at 300 bit/s at 300 baud and 212A transmits at 1200 bit/s at 600
baud .
*V.21 : Capable of only 300 bit/s, it is an international standard used mainly outside of the U.S.
*V.22 : Capable of 1200 bit/s at 600 baud. Used mainly outside the U.S.
*V.22bis : Used in the U.S. and out, it is capable of 2400 bit/s at 600 baud.
*V.23 : Used mainly in Europe, it allows the modem to send and receive data at the same time at 75 bit/s.
*V.29 : A one-way (half-duplex ) standard that is used mostly for fax machines. Capable of 9600 bit/s.
*V.32 : Afull-duplex standard capable of 9600 bit/s 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 bit/s. 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 bit/s.
*V.34 : Capable of 28,000 bit/s or fallback to 24,000 and 19,200 bit/s. This standard is backwards compatible with V.32 and V.32bis.
*V.34bis : Capable of 33,600 bit/s or fallback to 31,200 bit/s.
*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 bit/s.
*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 bit/s.
*V.92 : Transmits at the same speed as V.90 but offers a reduced handshake time and an on-hold feature.
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