baud

baud (bôd, bōd), measure of the rate at which signals are transmitted over a telecommunications link. It is equivalent to the number of elements or pulses transmitted in one second, e.g., in computer input/output, 2400 baud equals 2400 bits per second (bps) if each pulse encodes one bit (either 0 or 1). Many modems permit the encoding of several bits per baud. A 9600-bps modem that operates at 2400 baud sends four bits per baud by using a range of 16 tones (representing the four-bit combinations 0000 to 1111) to transmit data, and data compression can boost the effective transmission rate even higher. Because of this, the data transfer rate of a modem is measured in bits per second.

---

The signaling rate of a line, which is the number of transitions (voltage or frequency changes) that are made per second. The term has often been erroneously used to specify bits per second. However, only at very low speeds is baud equal to bps; for example, 300 baud is the same as 300 bps. Beyond that, one baud can be made to represent more than one bit. For example, a V.22bis modem generates 1,200 bps at 600 baud.

---

(communications, unit)

baud - /bawd/ (plural "baud") The unit in which the information carrying capacity or "signalling rate" of a communication channel is measured. One baud is one symbol (state-transition or level-transition) per second. This coincides with bits per second only for two-level modulation with no framing or stop bits. A symbol is a unique state of the communication channel, distinguishable by the receiver from all other possible states. For example, it may be one of two voltage levels on a wire for a direct digital connection or it might be the phase or frequency of a carrier. The term "baud" was originally a unit of telegraph signalling speed, set at one Morse code dot per second. Or, more generally, the reciprocal of the duration of the shortest signalling element. It was proposed at the International Telegraph Conference of 1927, and named after J.M.E. Baudot (1845-1903), the French engineer who constructed the first successful teleprinter. The UK PSTN will support a maximum rate of 600 baud but each baud may carry between 1 and 16 bits depending on the coding (e.g. QAM). Where data is transmitted as packets, e.g. characters, the actual "data rate" of a channel is R D / P where R is the "raw" rate in bits per second, D is the number of data bits in a packet and P is the total number of bits in a packet (including packet overhead). The term "baud" causes much confusion and is usually best avoided. Use "bits per second" (bps), "bytes per second" or "characters per second" (cps) if that's what you mean.