<sect1 id="connectivity-ppp-modem">
<title>The Modem Device</title>
<para>
In order to establish a PPP link between two computers using
the telephone line as medium for data transmission, you need
to install and configure one Modem device in each computer you
are connecting in. On the other hand, if you're planning to
connect the same computer to different networks simultaneously
(e.g., to build a proxy between them), you will need to
install and configure one Modem device for each different
network you plan to establish such simultaneous connection on.
</para>
<sect2 id="connectivity-ppp-modem-install">
<title>Installing Modem Devices</title>
<para>
To install a Modem device in the computer, you need to attach
the Modem hardware to the computer and later the telephone
line to the Modem hardware. To attach the Modem hardware to
your computer, you need to connect the serial or USB cable
that comes from the Modem hardware to the appropriate input on
your computer (whether serial or USB). To connect the Modem
hardware to the telephone line system, you need to unplug the
cable that connects your telephone device and plug it on the
Modem device, specifically in the port reserved for data
transmission. Later, using a similar cable, you could connect
your telephone device to the Modem's telephone port, so you
can realize telephone calls when no data transmition take
place through Modem's data port.
</para>
<para>
To be on the safe side, do everything related to hardware
installation with the computer turned off. Then, when
everthing has been put in place, turn the computer on. Once
the operating system is up and running, you can verify the
Modem hardware using either the <command>lsusb</command> or
<command>lspci</command> commands, based on whether you
attached the Modem device to an USB or serial port,
respectivly. These commands need to be run with
administrative privileges, so probably need to
<command>sudo</command> them or login as <systemitem
class="username">root</systemitem> user in order to execute
them. For example, assuming you are logged in as <systemitem
class="username">root</systemitem> user, and you are using an
USB Modem like that one we mentioned before, the output of
<command>lsusb</command> command would be similar to that
following:
</para>
<screen>
Bus 003 Device 001: ID 0000:0000
Bus 001 Device 001: ID 0000:0000
Bus 001 Device 002: ID 058f:6366 Alcor Micro Corp. Multi Flash Reader
Bus 002 Device 001: ID 0000:0000
Bus 005 Device 003: ID 06e0:f104 Multi-Tech Systems, Inc.
MT5634ZBA-USB MultiModemUSB (new firmware)
Bus 005 Device 001: ID 0000:0000
Bus 005 Device 002: ID 046d:c018 Logitech, Inc. Optical Wheel Mouse
Bus 004 Device 001: ID 0000:0000
</screen>
<para>
The relevant line in this output is that one mentioning the
existence of your Modem. For example, <code>Multi-Tech System,
Inc. MT5634ZBA-USB MultiModemUSB (new
firmware</code>)<footnote>
<para>
I want to thank my friend Brians Suarez Alonso for
bringing this Modem to me and for his paitient, resisting
my repetitive calls at night to realize connection tests.
</para>
</footnote>. This line confirms that your Modem hardware is
supported by &TCD; and it is possible to transmit data through
it. Otherwise, if the Modem you installed doesn't appear in
this list, it is probably because such hardware is not
supported by &TCD;, yet.
</para>
<para>
Once you have confirmed the Modem hardware has been installed
in the computer (either client or server), you need to
determine the device name the operating system assigned to it.
This information is required by programs like
<application>mgetty</application> and
<application>wvdial</application>, so they can know what
device to talk to. Assuming you've connected your Modem
device through an USB port, the operating system might use the
<filename>/dev/ttyACM0</filename> device file to talk to it.
On the other hand, assuming you've connected your Modem device
through a serial port, the operating system might use the
<filename>/dev/ttyS0</filename> device file to talk to it. To
be absolutly sure about what device name the operating system
assigned to your Modem hardware, you can use the
<application>wvdialconf</application> program from
<package>wvdial</package> package or the
<command>lshal</command> command from <package>hal</package>
package.
</para>
</sect2>
<sect2 id="connectivity-ppp-modem-config">
<title>Configuring Modem Devices</title>
<para>
Modem devices are configured through
<command>system-config-network</command> command. This command
produces Modem configuration files under the
<filename>/etc/sysconfig/network-scripts</filename> directory.
Configuration related to Modem devices can take different
file names, but they can be clearly identified by the value
set on the <varname>DEVICE</varname> variable, inside the
configuration file. This variable can take names like
<code>ppp0</code> for the first Modem device,
<code>ppp1</code> for the second Modem device, and so on for
other Modem devices. The Modem configuration files are used
by <application>pppd</application> and
<application>wvdial</application> programs when a PPP
connection is established between two computers. If you are
runing mgetty and pppd to attend incoming calls, it is very
important that you also specify the IP address and the network
mask in the configuration file of the Modem device you are
using to establish the connection. Otherwise, if the remote
peer doesn't set the IP information for you, it would be
difficult for both computer to establish a permanent
interchange of data across the link created.
</para>
<screen>
# Please read /usr/share/doc/initscripts-*/sysconfig.txt
# for the documentation of these parameters.
TYPE=Modem
DEVICE=ppp0
BOOTPROTO=none
ONBOOT=no
USERCTL=yes
PEERDNS=yes
AC=off
BSDCOMP=off
VJCCOMP=off
CCP=off
PC=off
VJ=off
LINESPEED=115200
MODEMPORT=/dev/ttyACM0
PROVIDER=ProviderName
DEFROUTE=yes
PERSIST=no
PAPNAME=faith
WVDIALSECT=ProviderName
MODEMNAME=Modem0
DEMAND=no
IPV6INIT=no
IDLETIMEOUT=600
NETMASK=255.255.255.0
IPADDR=192.168.1.1
</screen>
</sect2>
</sect1>