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