<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 Multi-Tech System, Inc. MT5634ZBA-USB MultiModemUSB

        (new firmware) device. 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

        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

        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=a

WVDIALSECT=ProviderName

MODEMNAME=Modem0

DEMAND=no

IPV6INIT=no

IDLETIMEOUT=600

NETMASK=255.255.255.0

IPADDR=192.168.0.2

</screen>

    </sect2>

</sect1>