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<H1> Modem-HOWTO</H1>

<H2>David S.Lawyer
  <CODE>
<A HREF="mailto:dave@lafn.org">mailto:dave@lafn.org</A></CODE></H2> v0.39, January 2007
<HR>
<EM> Help with selecting, connecting, configuring, trouble-shooting, and
 understanding analog modems for a PC.</EM>
<HR>
<P>
<H2><A NAME="toc1">1.</A> <A HREF="Modem-HOWTO-1.html">Introduction</A></H2>

<UL>
<LI><A NAME="toc1.1">1.1</A> <A HREF="Modem-HOWTO-1.html#ss1.1">DSL, Cable, and ISDN Modems in other HOWTOs</A>
<LI><A NAME="toc1.2">1.2</A> <A HREF="Modem-HOWTO-1.html#ss1.2">Also not well covered: PCMCIA Modems, PPP</A>
<LI><A NAME="toc1.3">1.3</A> <A HREF="Modem-HOWTO-1.html#ss1.3">Copyright, Disclaimer, Trademarks, &amp; Credits</A>
<LI><A NAME="toc1.4">1.4</A> <A HREF="Modem-HOWTO-1.html#ss1.4">Contacting the Author</A>
<LI><A NAME="toc1.5">1.5</A> <A HREF="Modem-HOWTO-1.html#ss1.5">New Versions of this HOWTO </A>
<LI><A NAME="toc1.6">1.6</A> <A HREF="Modem-HOWTO-1.html#ss1.6">New in Recent Versions</A>
<LI><A NAME="toc1.7">1.7</A> <A HREF="Modem-HOWTO-1.html#ss1.7">What is a Modem ? </A>
<LI><A NAME="toc1.8">1.8</A> <A HREF="Modem-HOWTO-1.html#ss1.8">Does My Computer Contain an Internal Modem ?</A>
<LI><A NAME="toc1.9">1.9</A> <A HREF="Modem-HOWTO-1.html#ss1.9">Quick Install </A>
<LI><A NAME="toc1.10">1.10</A> <A HREF="Modem-HOWTO-1.html#ss1.10">dev/modem</A>
</UL>
<P>
<H2><A NAME="toc2">2.</A> <A HREF="Modem-HOWTO-2.html">Modems for a Linux PC</A></H2>

<UL>
<LI><A NAME="toc2.1">2.1</A> <A HREF="Modem-HOWTO-2.html#ss2.1">Many Winmodems Will Not Work with Linux</A>
<LI><A NAME="toc2.2">2.2</A> <A HREF="Modem-HOWTO-2.html#ss2.2">External vs. Internal </A>
<LI><A NAME="toc2.3">2.3</A> <A HREF="Modem-HOWTO-2.html#ss2.3">Is a Driver Needed ?</A>
<LI><A NAME="toc2.4">2.4</A> <A HREF="Modem-HOWTO-2.html#ss2.4">External Modems</A>
<LI><A NAME="toc2.5">2.5</A> <A HREF="Modem-HOWTO-2.html#ss2.5">Internal Modems</A>
<LI><A NAME="toc2.6">2.6</A> <A HREF="Modem-HOWTO-2.html#ss2.6">Software-based Modems (winmodems, linmodems)</A>
<LI><A NAME="toc2.7">2.7</A> <A HREF="Modem-HOWTO-2.html#ss2.7">PCI Modems </A>
<LI><A NAME="toc2.8">2.8</A> <A HREF="Modem-HOWTO-2.html#ss2.8">AMR Modems</A>
<LI><A NAME="toc2.9">2.9</A> <A HREF="Modem-HOWTO-2.html#ss2.9">USB Modems </A>
<LI><A NAME="toc2.10">2.10</A> <A HREF="Modem-HOWTO-2.html#ss2.10">Which Internal Modems might not work with Linux </A>
</UL>
<P>
<H2><A NAME="toc3">3.</A> <A HREF="Modem-HOWTO-3.html">Modem Pools, RAS</A></H2>

<UL>
<LI><A NAME="toc3.1">3.1</A> <A HREF="Modem-HOWTO-3.html#ss3.1">Introduction</A>
<LI><A NAME="toc3.2">3.2</A> <A HREF="Modem-HOWTO-3.html#ss3.2">Analog Modem Pools, Multi-modem Cards </A>
<LI><A NAME="toc3.3">3.3</A> <A HREF="Modem-HOWTO-3.html#ss3.3">Digital Modems, RAS </A>
</UL>
<P>
<H2><A NAME="toc4">4.</A> <A HREF="Modem-HOWTO-4.html">Serial Port and Modem Basics </A></H2>

<UL>
<LI><A NAME="toc4.1">4.1</A> <A HREF="Modem-HOWTO-4.html#ss4.1">Modem Converts Digital to Analog (and conversely)</A>
<LI><A NAME="toc4.2">4.2</A> <A HREF="Modem-HOWTO-4.html#ss4.2">What is a Serial Port ?</A>
<LI><A NAME="toc4.3">4.3</A> <A HREF="Modem-HOWTO-4.html#ss4.3">IO Address &amp; IRQ</A>
<LI><A NAME="toc4.4">4.4</A> <A HREF="Modem-HOWTO-4.html#ss4.4">Names: ttyS0, ttyS1, etc.</A>
<LI><A NAME="toc4.5">4.5</A> <A HREF="Modem-HOWTO-4.html#ss4.5">Interrupts </A>
<LI><A NAME="toc4.6">4.6</A> <A HREF="Modem-HOWTO-4.html#ss4.6">Data Compression (by the Modem)</A>
<LI><A NAME="toc4.7">4.7</A> <A HREF="Modem-HOWTO-4.html#ss4.7">Error Correction</A>
<LI><A NAME="toc4.8">4.8</A> <A HREF="Modem-HOWTO-4.html#ss4.8">Data Flow (Speeds)</A>
<LI><A NAME="toc4.9">4.9</A> <A HREF="Modem-HOWTO-4.html#ss4.9">Flow Control </A>
<LI><A NAME="toc4.10">4.10</A> <A HREF="Modem-HOWTO-4.html#ss4.10">Data Flow Path; Buffers </A>
<LI><A NAME="toc4.11">4.11</A> <A HREF="Modem-HOWTO-4.html#ss4.11">Modem Commands</A>
<LI><A NAME="toc4.12">4.12</A> <A HREF="Modem-HOWTO-4.html#ss4.12">Serial Driver Module</A>
</UL>
<P>
<H2><A NAME="toc5">5.</A> <A HREF="Modem-HOWTO-5.html">Configuring Overview</A></H2>

<P>
<H2><A NAME="toc6">6.</A> <A HREF="Modem-HOWTO-6.html">Locating the Serial Port: IO address, IRQs </A></H2>

<UL>
<LI><A NAME="toc6.1">6.1</A> <A HREF="Modem-HOWTO-6.html#ss6.1">What Bus is my Serial Port On?</A>
<LI><A NAME="toc6.2">6.2</A> <A HREF="Modem-HOWTO-6.html#ss6.2">IO &amp; IRQ Overview</A>
<LI><A NAME="toc6.3">6.3</A> <A HREF="Modem-HOWTO-6.html#ss6.3">PCI Bus Support </A>
<LI><A NAME="toc6.4">6.4</A> <A HREF="Modem-HOWTO-6.html#ss6.4">Common mistakes made re low-level configuring</A>
<LI><A NAME="toc6.5">6.5</A> <A HREF="Modem-HOWTO-6.html#ss6.5">IRQ &amp; IO Address Must be Correct </A>
<LI><A NAME="toc6.6">6.6</A> <A HREF="Modem-HOWTO-6.html#ss6.6">What is the IO Address and IRQ per the driver ?</A>
<LI><A NAME="toc6.7">6.7</A> <A HREF="Modem-HOWTO-6.html#ss6.7">What is the IO Address &amp; IRQ of my Serial Port Hardware?</A>
<LI><A NAME="toc6.8">6.8</A> <A HREF="Modem-HOWTO-6.html#ss6.8">Choosing Serial IRQs </A>
<LI><A NAME="toc6.9">6.9</A> <A HREF="Modem-HOWTO-6.html#ss6.9">Choosing Addresses --Video card conflict with ttyS3</A>
<LI><A NAME="toc6.10">6.10</A> <A HREF="Modem-HOWTO-6.html#ss6.10">Set IO Address &amp; IRQ in the hardware (mostly for PnP)</A>
<LI><A NAME="toc6.11">6.11</A> <A HREF="Modem-HOWTO-6.html#ss6.11">Giving the IRQ and IO Address to Setserial</A>
</UL>
<P>
<H2><A NAME="toc7">7.</A> <A HREF="Modem-HOWTO-7.html">Configuring the Serial Driver (high-level) "stty"</A></H2>

<UL>
<LI><A NAME="toc7.1">7.1</A> <A HREF="Modem-HOWTO-7.html#ss7.1">Introduction</A>
<LI><A NAME="toc7.2">7.2</A> <A HREF="Modem-HOWTO-7.html#ss7.2">Hardware flow control (RTS/CTS)</A>
<LI><A NAME="toc7.3">7.3</A> <A HREF="Modem-HOWTO-7.html#ss7.3">Speed Settings </A>
<LI><A NAME="toc7.4">7.4</A> <A HREF="Modem-HOWTO-7.html#ss7.4">Ignore CD Setting: clocal</A>
<LI><A NAME="toc7.5">7.5</A> <A HREF="Modem-HOWTO-7.html#ss7.5">What is stty ? </A>
</UL>
<P>
<H2><A NAME="toc8">8.</A> <A HREF="Modem-HOWTO-8.html">Modem Configuration (excluding serial port) </A></H2>

<UL>
<LI><A NAME="toc8.1">8.1</A> <A HREF="Modem-HOWTO-8.html#ss8.1">Finding Your Modem</A>
<LI><A NAME="toc8.2">8.2</A> <A HREF="Modem-HOWTO-8.html#ss8.2">AT Commands</A>
<LI><A NAME="toc8.3">8.3</A> <A HREF="Modem-HOWTO-8.html#ss8.3">Init Strings: Saving and Recalling </A>
<LI><A NAME="toc8.4">8.4</A> <A HREF="Modem-HOWTO-8.html#ss8.4">Other AT Modem Commands </A>
<LI><A NAME="toc8.5">8.5</A> <A HREF="Modem-HOWTO-8.html#ss8.5">Blacklisting</A>
<LI><A NAME="toc8.6">8.6</A> <A HREF="Modem-HOWTO-8.html#ss8.6">What AT Commands are Now Set in my Modem?</A>
<LI><A NAME="toc8.7">8.7</A> <A HREF="Modem-HOWTO-8.html#ss8.7">Modem States (or Modes)</A>
</UL>
<P>
<H2><A NAME="toc9">9.</A> <A HREF="Modem-HOWTO-9.html">Serial Port Devices /dev/ttyS4, (or /dev/ttys/4) etc. </A></H2>

<UL>
<LI><A NAME="toc9.1">9.1</A> <A HREF="Modem-HOWTO-9.html#ss9.1">Serial Port Names: ttyS4, etc</A>
<LI><A NAME="toc9.2">9.2</A> <A HREF="Modem-HOWTO-9.html#ss9.2">The PCI Bus</A>
<LI><A NAME="toc9.3">9.3</A> <A HREF="Modem-HOWTO-9.html#ss9.3">Serial Port Device Names &amp; Numbers </A>
<LI><A NAME="toc9.4">9.4</A> <A HREF="Modem-HOWTO-9.html#ss9.4">More on Serial Port Names </A>
<LI><A NAME="toc9.5">9.5</A> <A HREF="Modem-HOWTO-9.html#ss9.5">USB (Universal Serial Bus) Serial Ports</A>
<LI><A NAME="toc9.6">9.6</A> <A HREF="Modem-HOWTO-9.html#ss9.6">Link ttySN to /dev/modem</A>
<LI><A NAME="toc9.7">9.7</A> <A HREF="Modem-HOWTO-9.html#ss9.7">Devfs (The Improved but Obsolete Device File System)</A>
<LI><A NAME="toc9.8">9.8</A> <A HREF="Modem-HOWTO-9.html#ss9.8">cua Device Obsolete </A>
</UL>
<P>
<H2><A NAME="toc10">10.</A> <A HREF="Modem-HOWTO-10.html">Interesting Programs You Should Know About</A></H2>

<UL>
<LI><A NAME="toc10.1">10.1</A> <A HREF="Modem-HOWTO-10.html#ss10.1">What is setserial ? </A>
<LI><A NAME="toc10.2">10.2</A> <A HREF="Modem-HOWTO-10.html#ss10.2">What is isapnp ?</A>
<LI><A NAME="toc10.3">10.3</A> <A HREF="Modem-HOWTO-10.html#ss10.3">What is wvdialconf ? </A>
</UL>
<P>
<H2><A NAME="toc11">11.</A> <A HREF="Modem-HOWTO-11.html">Trying Out Your Modem (Dialing Out) </A></H2>

<UL>
<LI><A NAME="toc11.1">11.1</A> <A HREF="Modem-HOWTO-11.html#ss11.1">Are You Ready to Dial Out ?</A>
<LI><A NAME="toc11.2">11.2</A> <A HREF="Modem-HOWTO-11.html#ss11.2">Dialing Out with wvdial </A>
<LI><A NAME="toc11.3">11.3</A> <A HREF="Modem-HOWTO-11.html#ss11.3">Dialing Out with Minicom </A>
<LI><A NAME="toc11.4">11.4</A> <A HREF="Modem-HOWTO-11.html#ss11.4">Dialing Out with Kermit </A>
</UL>
<P>
<H2><A NAME="toc12">12.</A> <A HREF="Modem-HOWTO-12.html">Dial-In </A></H2>

<UL>
<LI><A NAME="toc12.1">12.1</A> <A HREF="Modem-HOWTO-12.html#ss12.1">Dial-In Overview</A>
<LI><A NAME="toc12.2">12.2</A> <A HREF="Modem-HOWTO-12.html#ss12.2">What Happens when Someone Dials In ?</A>
<LI><A NAME="toc12.3">12.3</A> <A HREF="Modem-HOWTO-12.html#ss12.3">56k Doesn't Work for Dialin</A>
<LI><A NAME="toc12.4">12.4</A> <A HREF="Modem-HOWTO-12.html#ss12.4">Getty </A>
<LI><A NAME="toc12.5">12.5</A> <A HREF="Modem-HOWTO-12.html#ss12.5">Why "Manual" Answer is Best</A>
<LI><A NAME="toc12.6">12.6</A> <A HREF="Modem-HOWTO-12.html#ss12.6">Dialing Out while Waiting for an Incoming Call </A>
<LI><A NAME="toc12.7">12.7</A> <A HREF="Modem-HOWTO-12.html#ss12.7">Ending a Dial-in Call </A>
<LI><A NAME="toc12.8">12.8</A> <A HREF="Modem-HOWTO-12.html#ss12.8">Dial-in Modem Configuration </A>
<LI><A NAME="toc12.9">12.9</A> <A HREF="Modem-HOWTO-12.html#ss12.9">Callback</A>
<LI><A NAME="toc12.10">12.10</A> <A HREF="Modem-HOWTO-12.html#ss12.10">Distinctive Ring</A>
<LI><A NAME="toc12.11">12.11</A> <A HREF="Modem-HOWTO-12.html#ss12.11">Voice Mail </A>
<LI><A NAME="toc12.12">12.12</A> <A HREF="Modem-HOWTO-12.html#ss12.12">Simple Manual Dial-In </A>
<LI><A NAME="toc12.13">12.13</A> <A HREF="Modem-HOWTO-12.html#ss12.13">Complex GUI Dial-In, VNC</A>
<LI><A NAME="toc12.14">12.14</A> <A HREF="Modem-HOWTO-12.html#ss12.14">Interoperability with MS Windows</A>
</UL>
<P>
<H2><A NAME="toc13">13.</A> <A HREF="Modem-HOWTO-13.html">Uugetty for Dial-In (from the old Serial-HOWTO) </A></H2>

<UL>
<LI><A NAME="toc13.1">13.1</A> <A HREF="Modem-HOWTO-13.html#ss13.1">Installing getty_ps</A>
<LI><A NAME="toc13.2">13.2</A> <A HREF="Modem-HOWTO-13.html#ss13.2">Setting up uugetty</A>
<LI><A NAME="toc13.3">13.3</A> <A HREF="Modem-HOWTO-13.html#ss13.3">Customizing uugetty</A>
</UL>
<P>
<H2><A NAME="toc14">14.</A> <A HREF="Modem-HOWTO-14.html">What Speed Should I Use with My Modem? </A></H2>

<UL>
<LI><A NAME="toc14.1">14.1</A> <A HREF="Modem-HOWTO-14.html#ss14.1">Speed and Data Compression</A>
<LI><A NAME="toc14.2">14.2</A> <A HREF="Modem-HOWTO-14.html#ss14.2">Where do I Set Speed ?</A>
<LI><A NAME="toc14.3">14.3</A> <A HREF="Modem-HOWTO-14.html#ss14.3">Can't Set a High Enough Speed </A>
<LI><A NAME="toc14.4">14.4</A> <A HREF="Modem-HOWTO-14.html#ss14.4">Speed Table </A>
</UL>
<P>
<H2><A NAME="toc15">15.</A> <A HREF="Modem-HOWTO-15.html">Communications Programs And Utilities</A></H2>

<UL>
<LI><A NAME="toc15.1">15.1</A> <A HREF="Modem-HOWTO-15.html#ss15.1">Minicom vs. Kermit</A>
<LI><A NAME="toc15.2">15.2</A> <A HREF="Modem-HOWTO-15.html#ss15.2">List of Communication Software</A>
<LI><A NAME="toc15.3">15.3</A> <A HREF="Modem-HOWTO-15.html#ss15.3">SLiRP and term </A>
<LI><A NAME="toc15.4">15.4</A> <A HREF="Modem-HOWTO-15.html#ss15.4">MS Windows</A>
</UL>
<P>
<H2><A NAME="toc16">16.</A> <A HREF="Modem-HOWTO-16.html">Two Modems (Modem Doubling)</A></H2>

<UL>
<LI><A NAME="toc16.1">16.1</A> <A HREF="Modem-HOWTO-16.html#ss16.1">Introduction</A>
<LI><A NAME="toc16.2">16.2</A> <A HREF="Modem-HOWTO-16.html#ss16.2">Modem Bonding</A>
</UL>
<P>
<H2><A NAME="toc17">17.</A> <A HREF="Modem-HOWTO-17.html">ISDN "Modems"</A></H2>

<UL>
<LI><A NAME="toc17.1">17.1</A> <A HREF="Modem-HOWTO-17.html#ss17.1">External ISDN "Modems"</A>
<LI><A NAME="toc17.2">17.2</A> <A HREF="Modem-HOWTO-17.html#ss17.2">Internal ISDN "Modems"</A>
</UL>
<P>
<H2><A NAME="toc18">18.</A> <A HREF="Modem-HOWTO-18.html">Troubleshooting </A></H2>

<UL>
<LI><A NAME="toc18.1">18.1</A> <A HREF="Modem-HOWTO-18.html#ss18.1">My Modem is Physically There but Can't be Found </A>
<LI><A NAME="toc18.2">18.2</A> <A HREF="Modem-HOWTO-18.html#ss18.2">"Modem is busy"</A>
<LI><A NAME="toc18.3">18.3</A> <A HREF="Modem-HOWTO-18.html#ss18.3">"You are already online!  Hang up first." (from minicom)</A>
<LI><A NAME="toc18.4">18.4</A> <A HREF="Modem-HOWTO-18.html#ss18.4">I can't get near 56k on my 56k modem</A>
<LI><A NAME="toc18.5">18.5</A> <A HREF="Modem-HOWTO-18.html#ss18.5">Uploading (downloading) files is broken/slow</A>
<LI><A NAME="toc18.6">18.6</A> <A HREF="Modem-HOWTO-18.html#ss18.6">For Dial-in I Keep Getting "line NNN of inittab invalid"</A>
<LI><A NAME="toc18.7">18.7</A> <A HREF="Modem-HOWTO-18.html#ss18.7">I Keep Getting: ``Id "S4" respawning too fast: disabled for 5 minutes''</A>
<LI><A NAME="toc18.8">18.8</A> <A HREF="Modem-HOWTO-18.html#ss18.8">Dial-in: When remote user hangs up, getty doesn't respawn</A>
<LI><A NAME="toc18.9">18.9</A> <A HREF="Modem-HOWTO-18.html#ss18.9">NO DIALTONE</A>
<LI><A NAME="toc18.10">18.10</A> <A HREF="Modem-HOWTO-18.html#ss18.10">NO CARRIER</A>
<LI><A NAME="toc18.11">18.11</A> <A HREF="Modem-HOWTO-18.html#ss18.11">uugetty Still Doesn't Work </A>
<LI><A NAME="toc18.12">18.12</A> <A HREF="Modem-HOWTO-18.html#ss18.12">(The following subsections are in both the Serial and Modem HOWTOs)</A>
<LI><A NAME="toc18.13">18.13</A> <A HREF="Modem-HOWTO-18.html#ss18.13">Serial Port Can't be Found</A>
<LI><A NAME="toc18.14">18.14</A> <A HREF="Modem-HOWTO-18.html#ss18.14">Linux Creates an Interrupt Conflict (your PC has an ISA slot)</A>
<LI><A NAME="toc18.15">18.15</A> <A HREF="Modem-HOWTO-18.html#ss18.15">Extremely Slow: Text appears on the screen slowly after long delays</A>
<LI><A NAME="toc18.16">18.16</A> <A HREF="Modem-HOWTO-18.html#ss18.16">Somewhat Slow: I expected it to be a few times faster</A>
<LI><A NAME="toc18.17">18.17</A> <A HREF="Modem-HOWTO-18.html#ss18.17">The Startup Screen Shows Wrong IRQs for the Serial Ports</A>
<LI><A NAME="toc18.18">18.18</A> <A HREF="Modem-HOWTO-18.html#ss18.18">"Cannot open /dev/ttyS?: Device or resource busy</A>
<LI><A NAME="toc18.19">18.19</A> <A HREF="Modem-HOWTO-18.html#ss18.19">"Cannot open /dev/ttyS?: Permission denied"</A>
<LI><A NAME="toc18.20">18.20</A> <A HREF="Modem-HOWTO-18.html#ss18.20">"Cannot open /dev/ttyS?"</A>
<LI><A NAME="toc18.21">18.21</A> <A HREF="Modem-HOWTO-18.html#ss18.21">"Operation not supported by device" for ttyS?</A>
<LI><A NAME="toc18.22">18.22</A> <A HREF="Modem-HOWTO-18.html#ss18.22">"Cannot create lockfile. Sorry" </A>
<LI><A NAME="toc18.23">18.23</A> <A HREF="Modem-HOWTO-18.html#ss18.23">"Device /dev/ttyS? is locked."</A>
<LI><A NAME="toc18.24">18.24</A> <A HREF="Modem-HOWTO-18.html#ss18.24">"/dev/tty? Device or resource busy" </A>
<LI><A NAME="toc18.25">18.25</A> <A HREF="Modem-HOWTO-18.html#ss18.25">"Input/output error" from setserial, stty, pppd, etc.</A>
<LI><A NAME="toc18.26">18.26</A> <A HREF="Modem-HOWTO-18.html#ss18.26">"LSR safety check engaged"</A>
<LI><A NAME="toc18.27">18.27</A> <A HREF="Modem-HOWTO-18.html#ss18.27">Overrun errors on serial port</A>
<LI><A NAME="toc18.28">18.28</A> <A HREF="Modem-HOWTO-18.html#ss18.28">Modem doesn't pick up incoming calls</A>
<LI><A NAME="toc18.29">18.29</A> <A HREF="Modem-HOWTO-18.html#ss18.29">Port gets characters only sporadically</A>
<LI><A NAME="toc18.30">18.30</A> <A HREF="Modem-HOWTO-18.html#ss18.30">Troubleshooting Tools</A>
</UL>
<P>
<H2><A NAME="toc19">19.</A> <A HREF="Modem-HOWTO-19.html">Flash Upgrades</A></H2>

<P>
<H2><A NAME="toc20">20.</A> <A HREF="Modem-HOWTO-20.html">Other Sources of Information</A></H2>

<UL>
<LI><A NAME="toc20.1">20.1</A> <A HREF="Modem-HOWTO-20.html#ss20.1">Misc</A>
<LI><A NAME="toc20.2">20.2</A> <A HREF="Modem-HOWTO-20.html#ss20.2">Books</A>
<LI><A NAME="toc20.3">20.3</A> <A HREF="Modem-HOWTO-20.html#ss20.3">HOWTOs</A>
<LI><A NAME="toc20.4">20.4</A> <A HREF="Modem-HOWTO-20.html#ss20.4">Usenet newsgroups</A>
<LI><A NAME="toc20.5">20.5</A> <A HREF="Modem-HOWTO-20.html#ss20.5">Old Modem Database on Internet </A>
<LI><A NAME="toc20.6">20.6</A> <A HREF="Modem-HOWTO-20.html#ss20.6">Other Web Sites </A>
</UL>
<P>
<H2><A NAME="toc21">21.</A> <A HREF="Modem-HOWTO-21.html">Appendix A:  How Analog Modems Work (technical) (unfinished)</A></H2>

<UL>
<LI><A NAME="toc21.1">21.1</A> <A HREF="Modem-HOWTO-21.html#ss21.1">Modulation Details </A>
<LI><A NAME="toc21.2">21.2</A> <A HREF="Modem-HOWTO-21.html#ss21.2">56k Modems (V.90, V.92) </A>
<LI><A NAME="toc21.3">21.3</A> <A HREF="Modem-HOWTO-21.html#ss21.3">Full Duplex on One Circuit</A>
<LI><A NAME="toc21.4">21.4</A> <A HREF="Modem-HOWTO-21.html#ss21.4">Echo Cancellation</A>
</UL>
<P>
<H2><A NAME="toc22">22.</A> <A HREF="Modem-HOWTO-22.html">Appendix B: Analog Voice Infeasible Over Non-Voice Modem</A></H2>

<P>
<H2><A NAME="toc23">23.</A> <A HREF="Modem-HOWTO-23.html">Appendix C: "baud" vs. "bps"</A></H2>

<UL>
<LI><A NAME="toc23.1">23.1</A> <A HREF="Modem-HOWTO-23.html#ss23.1">A simple example</A>
<LI><A NAME="toc23.2">23.2</A> <A HREF="Modem-HOWTO-23.html#ss23.2">Real examples</A>
</UL>
<P>
<H2><A NAME="toc24">24.</A> <A HREF="Modem-HOWTO-24.html">Appendix D: Terminal Server Connection</A></H2>

<P>
<H2><A NAME="toc25">25.</A> <A HREF="Modem-HOWTO-25.html">Appendix E: Cable and DSL modems </A></H2>

<UL>
<LI><A NAME="toc25.1">25.1</A> <A HREF="Modem-HOWTO-25.html#ss25.1">Introduction</A>
<LI><A NAME="toc25.2">25.2</A> <A HREF="Modem-HOWTO-25.html#ss25.2">Digital Subscriber Line (DSL)</A>
<LI><A NAME="toc25.3">25.3</A> <A HREF="Modem-HOWTO-25.html#ss25.3">Cable Modems</A>
</UL>
<P>
<H2><A NAME="toc26">26.</A> <A HREF="Modem-HOWTO-26.html">Appendix F: Connecting 2 Modems Directly Back-to-Back (Leased Lines).</A></H2>

<P>
<H2><A NAME="toc27">27.</A> <A HREF="Modem-HOWTO-27.html">Appendix G: Fax pixels (dots)</A></H2>

<P>
<H2><A NAME="toc28">28.</A> <A HREF="Modem-HOWTO-28.html">Appendix H: Stty Hanging Problem (prior to 2000)</A></H2>

<P>
<H2><A NAME="toc29">29.</A> <A HREF="Modem-HOWTO-29.html">Appendix G: Antique Modems</A></H2>

<UL>
<LI><A NAME="toc29.1">29.1</A> <A HREF="Modem-HOWTO-29.html#ss29.1">Introduction</A>
<LI><A NAME="toc29.2">29.2</A> <A HREF="Modem-HOWTO-29.html#ss29.2">Historical Modem Protocols</A>
<LI><A NAME="toc29.3">29.3</A> <A HREF="Modem-HOWTO-29.html#ss29.3">Historical Overview</A>
<LI><A NAME="toc29.4">29.4</A> <A HREF="Modem-HOWTO-29.html#ss29.4">Proprietary protocols, etc.</A>
<LI><A NAME="toc29.5">29.5</A> <A HREF="Modem-HOWTO-29.html#ss29.5">Autobauding </A>
<LI><A NAME="toc29.6">29.6</A> <A HREF="Modem-HOWTO-29.html#ss29.6">Modem-to-modem Speed</A>
<LI><A NAME="toc29.7">29.7</A> <A HREF="Modem-HOWTO-29.html#ss29.7">Modem-to-serial_port Speed</A>
<LI><A NAME="toc29.8">29.8</A> <A HREF="Modem-HOWTO-29.html#ss29.8">Before AT Commands</A>
<LI><A NAME="toc29.9">29.9</A> <A HREF="Modem-HOWTO-29.html#ss29.9">Acoustic-Coupling</A>
<LI><A NAME="toc29.10">29.10</A> <A HREF="Modem-HOWTO-29.html#ss29.10">Data Compression and Error Correction</A>
<LI><A NAME="toc29.11">29.11</A> <A HREF="Modem-HOWTO-29.html#ss29.11">Historical Bibliography</A>
</UL>
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