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<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>