<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 

        class="username">root</systemitem> user in order to execute

        them. For example, assuming you are logged in as 

        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, Multi-Tech System,

        Inc.  MT5634ZBA-USB MultiModemUSB (new

        firmware)<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 &TC;; 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 &TC;;, 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

        ppp0 for the first Modem device,

        ppp1 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>