23.2 Real examples
The above example is overly simple. Real examples are more complicated but based on the same idea. This explains how a modem running at 2400 baud, can send 14400 bps (or higher). The modem achieves a bps rate greater than baud rate by encoding many bits in each signal change (or transition). Thus, when 2 or more bits are encoded per baud, the bps rate exceeds the baud rate. If your modem-to-modem connection is at 14400 bps, it's going to be sending 6 bits per signal transition (or symbol) at 2400 baud. A speed of 28800 bps is obtained by 3200 baud at 9 bits/baud. When people misuse the word baud, they may mean the modem speed (such as 33.6k).
Common modem bps rates were formerly 50, 75, 110, 300, 1200, 2400, 9600. These were also the bps rates over the serial_port-to-modem cables. Today the bps modem-to-modem (maximum) rates are 14.4k, 28.8k, 33.6k, and 56k, but the common rates over the serialPort-to-modem cables are not the same but are: 19.2k, 38.4k, 57.6k, 115.2k, 230.4k. The high speed of 230.4k is (as of late 2000) unfortunately not provided by most new (and old) hardware. Using modems with V.42bis compression (max 4:1 compression), rates up to 115.2k bps are possible for 33.6k modems. 203.2k (4 x 53.3k) is possible for 56k modems.
Except for 56k modems, most modems run at 2400, 3000, or 3200 baud. Even the 56k modems use these bauds for transmission and sometimes fall back to them for reception. Because of the bandwidth limitations on voice-grade phone lines, baud rates greater than 2400 are harder to achieve, and only work under conditions of good phone line quality.
How did this confusion between bps and baud start? Well, back when antique low speed modems were high speed modems, the bps rate actually did equal the baud rate. One bit would be encoded per phase change. People would use bps and baud interchangeably, because they were the same number. For example, a 300 bps modem also had a baud rate of 300. This all changed when faster modems came around, and the bit rate exceeded the baud rate. ''baud'' is named after Emile Baudot, the inventor of the asynchronous telegraph printer. One way this problem gets resolved is to use the term "symbol rate" instead of "baud" and thus avoid using the term "baud". However when talking about the "speeds" between the modem and the serial port (DTE speed) baud and the symbol rate are the same. And even "speed" is a misnomer since we really mean flow rate.
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