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176 lines
8.0 KiB
176 lines
8.0 KiB
<chapter id="modem-tricks">
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<title>Modem Tricks and Hints</title>
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<para>This section should get the fearful started on the (not so) arcane art of
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modem tweaking. The commands here are all Hayes AT standard, but all modems are
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not equal, so your mileage may vary.</para>
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<sect1 id="modem-sessions">
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<title>Modem Sessions</title>
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<para>A Modem session allows you to interact with the modem directly. You type
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commands, and it will respond. To obtain a modem session, when no connection is
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active, go into <guibutton>Setup</guibutton>, then <guilabel>Modem</guilabel>
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<guibutton>Terminal</guibutton> dialog. This will open a window for interactive
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configuration of the modem. Try typing
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<userinput><command>ATZ</command></userinput> (which resets your modem) Your
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should get an OK response. Use
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<menuchoice><guimenu>File</guimenu><guimenuitem>Close</guimenuitem></menuchoice>
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to end the session.</para>
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</sect1>
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<sect1 id="modem-profiles">
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<title>Modem Profiles</title>
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<para>One reason you might want to send the modem commands directly is if you
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have a set of modem configurations you want to keep, and not have to specify for
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every connection. A good way to do that is via modem profiles. Modems can have
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several stored profiles numbered 0,1,... <command>AT&V</command> can be used to
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view them all. The default profile is usually 0 (this can be changed via
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<command>AT&Y</command>.) The profile currently in use is called the
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<quote>active</quote> profile.</para>
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<para>When you change a setting, the active profile is modified. The
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<command>ATZ</command> command will have the modem load the default profile,
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erasing any changes you have made. To save changes, Load the profile you want to
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change via <command>ATZ<replaceable>n</replaceable></command> (where
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<replaceable>n</replaceable> is the profile number). Make the changes you want,
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then save it with <command>AT&W<replaceable>n</replaceable></command>. To
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have kppp use the profile you want, change the modem initialization string
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(<guibutton>Setup</guibutton> <guilabel>Modem</guilabel> <guibutton>Modem
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Commands</guibutton> <guilabel>Initialization String</guilabel>.) For example
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<command>ATZ1</command> will have the kppp reset the modem and use stored
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profile #1.</para>
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<para>If you want reset you modem to get back to some known starting point, use
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<command>AT&F&W</command> to set the active profile to the factory
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defaults, and store those settings as the default profile.</para>
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<para>Examples of profile changes are in the next section</para>
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</sect1>
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<sect1 id="modem-hangup">
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<title>Getting the modem to hang up</title>
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<para>Sometimes you may find that &kppp; has difficulties hanging up the modem.
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This is likely the result of a mismatch between &kppp; settings and those of the
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modem. A standard modem uses two methods to decide to hangup: <link
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linkend="hangup-command-method">Command</link>, and <link
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linkend="hangup-dtr-method"><acronym>DTR</acronym></link>. The Command method involves
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sending an escape sequence to the modem, which puts it in command mode, then
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issuing the hangup command (<command>ATH</command>).</para>
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<para>Outside of &kppp;, when configuring the <application>pppd</application>
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package manually, it's often helpful to use the command method, so that one can
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exit a terminal session, and then start <application>pppd</application> without
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having the modem hangup. In most other situations, the <acronym>DTR</acronym>
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method is preferred, as it is simpler.</para>
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<sect2 id="hangup-dtr-method">
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<title><acronym>DTR</acronym> (<command>AT&Dn</command>) method</title>
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<para>The <acronym>DTR</acronym> method will have the modem hangup whenever
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&kppp; stops using the modem. If you obtain a modem session, and query the
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state via <command>AT&V</command>, and you can see among the displayed
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settings for the active profile a <command>&D0</command>, then the
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<acronym>DTR</acronym> hangup method is disabled. To enable the
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<acronym>DTR</acronym> method, use the <guibutton>Terminal</guibutton> button to
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get a modem session, then:</para>
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<screen>
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<userinput><command>ATZ</command></userinput> <lineannotation># reset to default profile</lineannotation>
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<userinput><command>AT&D2</command></userinput> <lineannotation># Set to hang up on DTR drop</lineannotation>
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<userinput><command>AT&W</command></userinput> <lineannotation># Write to default profile</lineannotation>
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</screen>
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<sect3>
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<title>How the <acronym>DTR</acronym> method works</title>
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<para>Whenever the Data Terminal Ready (<acronym>DTR</acronym>) line on the
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serial line between the host computer and the modem goes high, the modem hangs
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up. When &kppp; opens the serial port, the <acronym>DTR</acronym> line is pulled
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low, on an external modem, you can see the <acronym>DTR</acronym> (or
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<acronym>TR</acronym>) light come on when this happens. When the
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<acronym>TR</acronym> light goes out (because &kppp; has closed the serial port,
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or something worse!), the modem will hangup.</para>
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</sect3>
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</sect2>
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<sect2 id="hangup-command-method">
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<title>Command method</title>
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<para>The other way to have a modem hang up when connected (used when
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<command>AT&D<replaceable>n</replaceable></command> where
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<replaceable>n</replaceable> is not <returnvalue>2</returnvalue>) is to have the
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modem accept the command when a session is in progress. To have it hang up
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properly, get a modem session, and set the guard time to a short interval like
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so:</para>
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<screen>
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<userinput><command>ATZ</command></userinput>
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<userinput><command>ATS12=5</command></userinput>
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<userinput><command>AT&W</command></userinput>
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</screen>
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<para>Then use the <guilabel>Guard Time</guilabel> slider in the Modem commands
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section to match the register (<varname>S12</varname> to this value
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<returnvalue>5</returnvalue>. The modem should then hangup properly.</para>
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<sect3>
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<title>How the Command Method Works</title>
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<para>When the local modem is connected to a remote modem, it is in the
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<quote>connect</quote> state, where it passes all characters it receives to the
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remote modem without interpretation. To have the modem accept the characters
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as commands for itself, one must put the modem into the command state. The
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escape code does this.</para>
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<para>The escape code is defined as being three intervals of time whose length
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is defined by <varname>S12</varname> in fiftieths of a second.</para>
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<itemizedlist>
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<listitem>
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<para>Quiet (must last more than <varname>S12</varname>/50 seconds)</para>
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</listitem>
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<listitem>
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<para>Escape character (defined by the register <varname>S2</varname>, the
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default is <quote>+</quote>), repeated three times (less than
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<varname>S12</varname>/50 seconds between each.</para>
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</listitem>
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<listitem>
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<para>Quiet (must last more than <varname>S12</varname>/50 seconds)</para>
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</listitem>
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</itemizedlist>
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<para>Once the modem is in the command state, you can send it commands. To have
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it hang up, send the command <command>ATH</command>. The escape codes and the
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hangup string used by &kppp; are shown in the <link
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linkend="modem-commands"><guilabel>Modem Commands</guilabel></link> dialog.
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These should match your modem.</para>
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</sect3>
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</sect2>
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</sect1>
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<sect1 id="tone-dialing-speedup">
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<title>Make Tone dialing faster</title>
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<para>If you can use tone dialing, the amount of time it takes to dial can be
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changed using the <varname>S11</varname> register. It gives the duration (in
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100hundreds of a second) to send each tone while dialing. The default is
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usually 95 (almost a second.) How fast you can dial depends on the phone
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company's switching equipment which handles your line. The minimum duration is
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50, almost twice as fast, and that speed often works. </para>
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<screen>
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<userinput><command>ATZ</command></userinput> <lineannotation># reset to default profile</lineannotation>
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<userinput><command>ATS11=50</command></userinput> <lineannotation># fastest possible dialing, use a higher number if it doesn't work</lineannotation>
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<userinput><command>AT&W</command></userinput> <lineannotation># write to default profile</lineannotation>
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</screen>
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</sect1>
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</chapter>
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