<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 

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

        them. For example, assuming you logged in as 

        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, Multi-Tech System,

        Inc.  MT5634ZBA-USB MultimodemUSB (new

        firmware)<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 &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 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 &TC;;, 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 ppp0 for the first modem device,

        ppp1 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>