Speed

We already mentioned that both ends of the link agree on the rate at which they will transmit data. This is measured by something known as the “baud rate,” which, although not strictly correct, is commonly classed as “bits per second” (bps).

Baud and BPS

The baud rate is a measure of how many times per second a signal changes; for example, the signal on a 300-baud modem would change 300 times per second.

The number of bits transmitted per second is dependent on both the baud rate of the modem and the number of bits that it can transmit per baud. For example, if a 300-baud modem is able to transmit 1 bit per baud, it can transmit 300 bps. However, if the same modem can transmit 4 bits per baud, then the same 300-baud modem can transmit four times as many bits, or 1,200 bps.

Characters per Second

The number of characters transmitted per second (cps) depends upon the number of bits per character (bpc). For example, if the link is configured for 1 start bit, 8 data bits, no parity, and 1 stop bit, a total of 10 bits will be sent for every character, which means we can transmit 960 cps (9,600 bps/10 bpc).