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.
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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.
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Be aware that the sound driver is a
kernel module that has its settings stored in
/etc/modules.conf. | 
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