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Voice-Grade Modems

Voice-grade modems are designed for the transmission of digital data over ordinary telephone lines. Thus, the modems make use of the same 4 kHz bandwidth available for voice signals. Because modems are used in pairs for communications, and because this use often occurs over the public telephone network, allowing many different modems to be paired, standards are essential. Table 1 lists the most popular voice-grade modem types, as designated by the ITU-T Recommendation that defines them. Perhaps the most significant of these modem standards is the V.32 specification for a 9600 BPS modem.

Table 1 Modem Specification

ITU-T Recommendation

Data Rate (bps)

Dial-up

Half-Duplex

Full-Duplex

V.29

9600

 

X

X

V.32

9600

X

 

X

V.32bis

14,400

X

 

X

V.33

14,400

 

 

X

V.34

33,600

X

X

X

V.90

33,600 (send), 56,000 (receive)

X

X

X


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