Modem Standards

Many different types of modems exist in market today. There are several standards for modems, and modems that conform to a standard can communicate with other modems having the same standard. Many new modems currently developed support several standards.

V.22/V.22bis Modems

V.22 is the Consultative Committee on International Telegraph and Telephone (CCITT) standard for 600 bps or 1,200 bps full-duplex modems for many years, but this standard is becoming obsolete. The modem uses frequency modulation (FSK). V.22bis is the CCITT standard for 2400 bps full-duplex modems. It uses QAM modulation.

V.32/V.32bis Modems (High Speed)

V.32 is the CCITT standard for 4,800 bps and 9,600 bps full-duplex modems over dial-up telephone circuits. It uses QAM modulation. V32bis is the CCITT standard that extends V.32 to data rate of 14,400 bits per second.

V.34/V.34bis Modems (Error Checking)

V.34 is the CCITT standard for the digital (not analog) transmission telephone network beyond a local loop. It supports the data rates up to 28,800 bps. V.34bis is an extension of the V.34 standard. This modem provides a better error checking and voice transmissions. It supports the higher data transmission rates of 33,600 bps.

V.42/V.42bis Modems (Data Compression)

V.42 is the CCITT standard for error correction that uses two protocols. The main protocol is LAPM and secondary protocol is MNP Classes 2 through 4. V.42bis is the CCITT standard for error correction and data compression. It provides a compression technique to increase transmission speed around 4 times the bps rating by using a dictionary of 4- byte character combinations.

Frequency Modulation

A communications transmission technique that modulates a data signal into a fixed carrier frequency by modifying the carrier frequency.

FSK (Frequency Shift Keying)

A simple communications modulation technique that merges binary data into a carrier frequency. It usually creates only two changes in the frequency, one for the 0 bit and another for the 1 bit.

QAM

?Refers to Quadrature Amplitude Modulation. A modulation technique that generates 4 bits per baud.

LAPM

Refers Link Access Procedure Modem. The protocol defined in CCITT V.42. It uses LAPD methods (LAP-D channel) used for the data channel of an ISDN transmission.

MNP

Refers to Microcom Networking Protocol. This is a data compression protocol that has been a standard in the United States. It was developed from microcom, Inc.