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Dictionary of Electrical Engineering

Commonly used terms in the Electrical industry.

the signaling rate, or rate of state transitions, on a communications medium. One baud corresponds to one transition per second. It is often confused with the data transmission rate, measured in bits per second.
Numerically, it is the reciprocal of the length (in seconds) of the shortest element in a signaling code. For very low-speed modems (up to 1200 bit/s) the baud rate and bit rate are usually identical. For example, at 9600 baud, each bit has a duration of 1/9600 seconds, or about 0.104 milliseconds.
Modems operating over analog telephone circuits are bandwidth limited to about 2500 baud; for higher user data speeds each transition must establish one or more decodable states according to amplitude or phase changes. Thus, if there are 16 possible states, each can encode 4 bits of user data and the bit rate is 4 times the baud rate.
At high speeds, the reverse is true, with run-length controlled codes needed to ensure reliable reception and clock recovery. For example FDDI uses a 4B/5B coding in which a "nibble" of 4 data bits is encoded into 5 bits for transmission. A user data rate of 100 Mbit/s corresponds to transmission at 125 Mbaud.

baud rate

See baud