13.3 Objective 3: Configure Modems and Sound Cards Like NICs and SCSI adapters, modems and sound adapters have a few special considerations during installation. This Objective covers some of these issues. 13.3.1 Modems A modem (a word derived from mo dulate and dem odulate) 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. 13.3.1.1 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 built in ( /dev/ttyS0 and /dev/ttyS1), an internal modem will appear as the third port ( /dev/ttys2). This means that from a programming point of view, internal modems are indistinguishable from external modems. While there is some variation in modem configuration across manufacturers, the differences are small, and most serial-port-style modems will work with Linux. One exception is a modem designed specifically to work with the Windows operating system. These so-called WinModems rely on the CPU and a special software driver to handle some of the communications processing, thus lack the full hardware capabilities of standard modems. As such, WinModems are not compatible with Linux unless a Linux-specific driver is available. Information on such support is available from http://www.linmodems.org/. One example of such support is an effort by IBM to support Mwave WinModems installed in its laptop line. 13.3.1.2 Modem hardware resources As with any add-on card, particularly cards configured manually, the user must be careful to avoid resource conflicts. Modems shouldn't cause much difficulty since they're simple serial ports. However, you should confirm that the correct interrupt and I/O addresses are set on your modem. If the modem shares an interrupt with another serial port, that port cannot be used at the same time as the modem. | Watch out for WinModems, which often don't work with Linux. Remember that PC serial ports may share an interrupt (but not an I/O port). This Objective requires knowledge regarding the setup of a modem for outbound dialup. For this information, see Section 19.3. | 13.3.2 Sound Devices Nearly every laptop and desktop PC shipped today includes a sound device. Fortunately, Linux sound drivers are available for most sound chipsets, including the industry standard chipset originally defined by Creative Labs with its SoundBlaster series. Part of the configuration for a sound card involves correctly specifying the sound card's resources to the sound driver, which is a kernel module. | Be aware that the sound driver is a kernel module that has its settings stored in /etc/modules.conf. |  |
