[net.general] Baud Rates Explained

plw (02/26/83)

	'Tis time to tilt at windmills. A recent article in net.followup
concerning modems mentioned the term 'baud rate' when talking about modem
speed.
	The baud rate of a modem is not necessarily synonomous with the bit
rate. Most modems give the bit speed as an indicator of how fast they transmit
data. That is, the Bell 212A is a 1200 bit per second modem in the high speed
mode and a 300 bit per second modem in the low speed mode. I have noticed
an abundance of people saying that it is a 1200 BAUD modem, which it isn't.
Just for the record, the 212A is a 600 baud modem.
	Baud rate is more accurately stated as symbol rate with the speed
given as symbols per second. In the case of the 212A, a symbol is 2 bits. The
212A transmits these symbols as a shift in the phase of the data signal with
respect to the carrier signal; each phase shift representing 2 bits of data.
	In the low speed mode, a symbol is 1 bit of data with a symbol being
transmitted by a shift in the frequency of the carrier. This means that in
this case the baud rate and bit rate are the same - 300.
	As users and purchasers of modems, we are really concerned with the
bit rate rather than the baud rate. The bit rate gives a better indication
of characters/second, but not necessarily an accurate one. Characters per
second is the bottom line in data transmission because that is the 'useful'
information we're interested in.
	Since most of us understand what it meant when someone says their
modem is 1200 baud, the accuracy of the statement is really a technicality.
This article is intended to clarify that technicality.

				From the 'baudy house' capitol,
				Pete Wilson
				Western Electric
				Montgomery, IL
				lime!we13!plw