<sect1 id="connectivity-dialup-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. 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-dialup-modem-install">
    <title>Installing Modem Devices</title>
    <para>
        To install a Modem device in a 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. 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, as well.
    </para>

    <para>
        To be on the safe side, do all the installation with the
        computer turned off. Then, when everthing has been put in
        place, turn the computer on. Once the system is up, you can
        verify the Modem hardware using either the
        <command>lsusb</command> or <command>lspci</command> commands.
        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 look like the
        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 here is that one mentioning the existence of
        a <code>Multi-Tech System, Inc. MT5634ZBA-USB MultiModemUSB
        (new firmware)</code> device. 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
        the <filename>/dev/ttyACM0</filename> 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> 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-dialup-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=a
WVDIALSECT=ProviderName
MODEMNAME=Modem0
DEMAND=no
IPV6INIT=no
IDLETIMEOUT=600
NETMASK=255.255.255.0
IPADDR=192.168.0.2
</screen>

    </sect2>

</sect1>