LPI Linux Certification in a Nutshell, 2nd Edition

Objective 3: Configure Modems and Sound Cards

Modems and sound cards, while non-essential, are two of the most common pieces of hardware installed in a Linux system; unfortunately, they are also two of the most problematic to configure. This Objective covers the tasks required to complete modem and sound card configuration.

Modems

A modem (a word derived from modulate and demodulate) is that familiar device that modulates a digital signal into an analog signal for transmitting information via telephone lines. A modem on the other end of the connection demodulates the signal back into its digital form. Modems can also add digital compression and error correction capabilities to increase speed and reliability.

Modem types

Modems are serial devices, where data enters and exits one bit at a time. Traditionally, modems were external devices attached via cable to industry standard RS-232 serial ports, such as those still found on most PCs. This arrangement continues to work well, because the data rates of telephone connections are still below the maximum rate of the serial ports. As a result, external devices yield solid performance. Internal modems (ISA or PCI bus cards that reside inside a PC) were developed to reduce costs associated with external modems (namely, the case, power supply, and shipping charges) and offer the same functionality as an external modem.

Most internal modems present themselves to the PC as a standard serial port. In a typical PC with the first two serial ports ...