baud

communications, unit /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.

(1998-02-14)