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This is a list of interface bit rates, is a measure of information transfer rates, or digital bandwidth capacity, ... Modem 300 (300 baud; Bell 103 or V.21)
From the mere four bits per symbol (9.6 kbit/s), the new standards used the functional equivalent of 6 to 10 bits per symbol, plus increasing baud rates from 2,400 to 3,429, to create 14.4, 28.8, and 33.6 kbit/s modems. This rate is near the theoretical Shannon limit of a phone line. [21]
In a modem, these may be time-limited sinewave tones with unique combinations of amplitude, phase and/or frequency. For example, in a 64QAM modem, M = 64, and so the bit rate is N = log 2 (64) = 6 times the baud rate. In a line code, these may be M different voltage levels.
Bit rates commonly supported include 75, 110, 300, 1200, 2400, 4800, 9600, 19200, 38400, 57600 and 115200 bit/s. [19] Many of these standard modem baud rates are multiples of either 1.2 kbps (e.g., 19200, 38400, 76800) or 0.9 kbps (e.g., 57600, 115200). [23] Crystal oscillators with a frequency of 1.843200 MHz are sold specifically for this ...
An example handshake of a dial-up modem. Modern dial-up modems typically have a maximum theoretical transfer speed of 56 kbit/s (using the V.90 or V.92 protocol), although in most cases, 40–50 kbit/s is the norm. Factors such as phone line noise as well as the quality of the modem itself play a large part in determining connection speeds.
A V.34 modem may transmit symbols at a baud rate of 3,420 Bd, and each symbol can carry up to ten bits, resulting in a gross bit rate of 3420 × 10 = 34,200 bit/s. However, the modem is said to operate at a net bit rate of 33,800 bit/s, excluding physical layer overhead.
V.32 (11/88) is an ITU-T recommendation for a modem operating as full-duplex on a 4-wire circuit, or half-duplex on a two-wire circuit, allowing bidirectional data transfer at either 9.6 kbit/s or 4.8 kbit/s at a symbol rate of 2,400 baud instead of the 600 baud of the V.22 standards.
The command set was copied largely verbatim, including the meaning of the registers, by almost all early 300 baud modem manufacturers, of which there were quite a few. The expansion to 1200 and 2400 baud required the addition of new commands, some of them prefixed with an ampersand ( & ) to denote those dedicated to new functionality.
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