<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 will
        need to install and configure a modem device in each computer
        you plan to connect. On the other hand, if you're planning to
        use PPP 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 in the same computer.
    </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, 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, thus, you probably need to do
        <command>sudo</command> on them or login as <systemitem
        class="username">root</systemitem> user in order to execute
        them. For example, assuming you logged in as <systemitem
        class="username">root</systemitem> user and you installed an
        USB modem hardware as 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 hardware 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 will assign
        the 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 will
        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
        <command>lshal</command> command from <package>hal</package>
        package.
    </para>
    </sect2>

    <sect2 id="connectivity-ppp-modem-config">
    <title>Configuring Modem Devices</title>

    <para>
        Inside &TCD;, modem devices can be configured using the
        <command>system-config-network</command> tool. This tool is a
        manages modem configuration files under the
        <filename>/etc/sysconfig/network-scripts</filename> and
        <filename>/etc/wvdial.conf</filename>.  Inside
        <filename>/etc/sysconfig/network-scripts</filename>, modem
        configuration files can take different file names. To identify
        them you need to open the file and checking the value set on
        <varname>DEVICE</varname> variable. This variable can take
        values like <code>ppp0</code> for the first modem device,
        <code>ppp1</code> for the second modem device, and so on for
        other modem devices.
    </para>

    <para>
        The configuration files of modem devices may vary based on
        whether the computer is acting as server, client or both.
        When you configure the modem device on the server computer,
        you should take care of specifying both the IP address
        (IPADDR) and the network mask (NETMASK) inside the
        configuration file.  Otherwise, the established connection
        might end up having the wrong IP information you need to
        transfer data correctly through it, assuming the other end
        isn't configured to specify it.  When you configure the modem
        device on the server computer, there is no need for you to set
        any configuration related to wvdial, unless you be thinking to
        make your server computer to act as a client of another server
        computer. In fact, in the server computer, you can create the
        modem configuration file by yourself based on the information
        provided at
        <filename>/usr/share/doc/initscripts-*/sysconfig.txt
        </filename>
    </para>

    <para>
        When you configure the modem device on the client computer,
        you don't need to take care of specifying either the IP
        address or network mask because the server computer will
        assign them for you. The assignment of client computer IP
        address is configured by <application>ppp</application> daemon
        when it is executed by <application>mgetty</application> after
        an incoming call has arrived to modem's port.
    </para>

    <example id="connectivity-ppp-modem-config.fig-1">
    <title>Modem configuration file</title>
    <screenshot>
    <screeninfo>Modem configuration file</screeninfo>
    <mediaobject>
    <textobject>
<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>
    </textobject>
    </mediaobject>
    </screenshot>
    </example>

    </sect2>

</sect1>