tdenetwork/doc/kppp/tricks.docbook

<chapter id="modem-tricks">
<title>Modem Tricks and Hints</title>

<para>This section should get the fearful started on the (not so) arcane art of
modem tweaking. The commands here are all Hayes AT standard, but all modems are
not equal, so your mileage may vary.</para>

<sect1 id="modem-sessions">
<title>Modem Sessions</title>

<para>A Modem session allows you to interact with the modem directly. You type
commands, and it will respond. To obtain a modem session, when no connection is
active, go into <guibutton>Setup</guibutton>, then <guilabel>Modem</guilabel>
<guibutton>Terminal</guibutton> dialog. This will open a window for interactive
configuration of the modem. Try typing
<userinput><command>ATZ</command></userinput> (which resets your modem) Your
should get an OK response. Use
<menuchoice><guimenu>File</guimenu><guimenuitem>Close</guimenuitem></menuchoice>
to end the session.</para>

</sect1>

<sect1 id="modem-profiles">
<title>Modem Profiles</title>
					
<para>One reason you might want to send the modem commands directly is if you
have a set of modem configurations you want to keep, and not have to specify for
every connection. A good way to do that is via modem profiles. Modems can have
several stored profiles numbered 0,1,... <command>AT&amp;V</command> can be used to
view them all. The default profile is usually 0 (this can be changed via
<command>AT&amp;Y</command>.) The profile currently in use is called the
<quote>active</quote> profile.</para>

<para>When you change a setting, the active profile is modified. The
<command>ATZ</command> command will have the modem load the default profile,
erasing any changes you have made. To save changes, Load the profile you want to
change via <command>ATZ<replaceable>n</replaceable></command> (where
<replaceable>n</replaceable> is the profile number). Make the changes you want,
then save it with <command>AT&amp;W<replaceable>n</replaceable></command>. To
have kppp use the profile you want, change the modem initialization string
(<guibutton>Setup</guibutton> <guilabel>Modem</guilabel> <guibutton>Modem
Commands</guibutton> <guilabel>Initialization String</guilabel>.) For example
<command>ATZ1</command> will have the kppp reset the modem and use stored
profile #1.</para>

<para>If you want reset you modem to get back to some known starting point, use
<command>AT&amp;F&amp;W</command> to set the active profile to the factory
defaults, and store those settings as the default profile.</para>

<para>Examples of profile changes are in the next section</para>

</sect1>

<sect1 id="modem-hangup">
<title>Getting the modem to hang up</title>

<para>Sometimes you may find that &kppp; has difficulties hanging up the modem.
This is likely the result of a mismatch between &kppp; settings and those of the
modem.  A standard modem uses two methods to decide to hangup: <link
linkend="hangup-command-method">Command</link>, and <link
linkend="hangup-dtr-method"><acronym>DTR</acronym></link>.  The Command method involves
sending an escape sequence to the modem, which puts it in command mode, then
issuing the hangup command (<command>ATH</command>).</para>

<para>Outside of &kppp;, when configuring the <application>pppd</application>
package manually, it's often helpful to use the command method, so that one can
exit a terminal session, and then start <application>pppd</application> without
having the modem hangup.  In most other situations, the <acronym>DTR</acronym>
method is preferred, as it is simpler.</para>

<sect2 id="hangup-dtr-method">
<title><acronym>DTR</acronym> (<command>AT&amp;Dn</command>) method</title>

<para>The <acronym>DTR</acronym> method will have the modem hangup whenever
&kppp; stops using the modem.  If you obtain a modem session, and query the
state via <command>AT&amp;V</command>, and you can see among the displayed
settings for the active profile a <command>&amp;D0</command>, then the
<acronym>DTR</acronym> hangup method is disabled.  To enable the
<acronym>DTR</acronym> method, use the <guibutton>Terminal</guibutton> button to
get a modem session, then:</para>

<screen>
<userinput><command>ATZ</command></userinput> <lineannotation># reset to default profile</lineannotation>
<userinput><command>AT&amp;D2</command></userinput>  <lineannotation># Set to hang up on DTR drop</lineannotation>
<userinput><command>AT&amp;W</command></userinput>  <lineannotation># Write to default profile</lineannotation>
</screen>

<sect3>
<title>How the <acronym>DTR</acronym> method works</title>

<para>Whenever the Data Terminal Ready (<acronym>DTR</acronym>) line on the
serial line between the host computer and the modem goes high, the modem hangs
up. When &kppp; opens the serial port, the <acronym>DTR</acronym> line is pulled
low, on an external modem, you can see the <acronym>DTR</acronym> (or
<acronym>TR</acronym>) light come on when this happens. When the
<acronym>TR</acronym> light goes out (because &kppp; has closed the serial port,
or something worse!), the modem will hangup.</para>
</sect3>

</sect2>

<sect2 id="hangup-command-method">
<title>Command method</title>

<para>The other way to have a modem hang up when connected (used when
<command>AT&amp;D<replaceable>n</replaceable></command> where
<replaceable>n</replaceable> is not <returnvalue>2</returnvalue>) is to have the
modem accept the command when a session is in progress.  To have it hang up
properly, get a modem session, and set the guard time to a short interval like
so:</para>

<screen>
<userinput><command>ATZ</command></userinput>
<userinput><command>ATS12=5</command></userinput>
<userinput><command>AT&amp;W</command></userinput>
</screen>

<para>Then use the <guilabel>Guard Time</guilabel> slider in the Modem commands
section to match the register (<varname>S12</varname> to this value
<returnvalue>5</returnvalue>.  The modem should then hangup properly.</para>

<sect3>
<title>How the Command Method Works</title>

<para>When the local modem is connected to a remote modem, it is in the
<quote>connect</quote> state, where it passes all characters it receives to the
remote modem without interpretation.  To have the modem accept the characters
as commands for itself, one must put the modem into the command state.  The
escape code does this.</para>

<para>The escape code is defined as being three intervals of time whose length
is defined by <varname>S12</varname> in fiftieths of a second.</para>

<itemizedlist>
<listitem>
<para>Quiet (must last more than <varname>S12</varname>/50 seconds)</para>
</listitem>
<listitem>
<para>Escape character (defined by the register <varname>S2</varname>, the
default is <quote>+</quote>), repeated three times (less than
<varname>S12</varname>/50 seconds between each.</para>
</listitem>
<listitem>
<para>Quiet (must last more than <varname>S12</varname>/50 seconds)</para>
</listitem>
</itemizedlist>

<para>Once the modem is in the command state, you can send it commands.  To have
it hang up, send the command <command>ATH</command>.  The escape codes and the
hangup string used by &kppp; are shown in the <link
linkend="modem-commands"><guilabel>Modem Commands</guilabel></link> dialog.
These should match your modem.</para>

</sect3>
</sect2>
</sect1>

<sect1 id="tone-dialing-speedup">
<title>Make Tone dialing faster</title>

<para>If you can use tone dialing, the amount of time it takes to dial can be
changed using the <varname>S11</varname> register. It gives the duration (in
100hundreds of a second) to send each tone while dialing. The default is
usually 95 (almost a second.) How fast you can dial depends on the phone
company's switching equipment which handles your line. The minimum duration is
50, almost twice as fast, and that speed often works. </para>

<screen>
<userinput><command>ATZ</command></userinput>        <lineannotation># reset to default profile</lineannotation>
<userinput><command>ATS11=50</command></userinput>   <lineannotation># fastest possible dialing, use a higher number if it doesn't work</lineannotation>
<userinput><command>AT&amp;W</command></userinput>   <lineannotation># write to default profile</lineannotation>
</screen>

</sect1>
</chapter>