baud
baud rate
/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)
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