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New HOWTO: Modem-HOWTO

Table of Contents

  • April 12, 2001
  Modem-HOWTO
  David S.Lawyer    mailto:dave@lafn.org
  v0.17, April 2001

  Help with selecting, connecting, configuring, trouble-shooting, and
  understanding modems for a PC.  See Serial-HOWTO for multiport serial
  boards.
  ______________________________________________________________________

  Table of Contents

  1. Introduction

     1.1 DSL, Cable, and ISDN Modems in other HOWTOs
     1.2 Also not covered: PCMCIA Modems, PPP
     1.3 Copyright, Disclaimer, Trademarks, & Credits
        1.3.1 Copyright
        1.3.2 Disclaimer
        1.3.3 Trademarks.
        1.3.4 Credits
     1.4 Contacting the Author
     1.5 New Versions of this HOWTO
     1.6 New in Recent Versions
     1.7 What is a Modem ?
     1.8 Quick Install
        1.8.1 External Modem Install
        1.8.2 Internal Modems (Both ISA and PCI)
        1.8.3 ISA Modems: What IOs and IRQs may be used?
        1.8.4 PCI Modems: What IOs and IRQs have been set?
        1.8.5 Both PCI and ISA: Use setserial to tell the driver
        1.8.6 Use MS Windows to set the BIOS (A last resort method)
        1.8.7 All Modems

  2. Modems for a Linux PC

     2.1 External vs. Internal
     2.2 External Modems
        2.2.1 PnP External Modems
        2.2.2 Cabling & Installation
        2.2.3 What the Lights (LED's) Mean (for some modems)
     2.3 Internal Modems
     2.4 Software-based Modems (winmodems)
        2.4.1 Introduction software modems (winmodems)
        2.4.2 Linmodems
        2.4.3 Software-based modem types
        2.4.4 Is this modem a software modem?
        2.4.5 Should I get a software modem?
     2.5 PCI Modems
     2.6 Which Internal Modems might not work with Linux
        2.6.1 MWave and DSP Modems
        2.6.2 Rockwell (RPI) Drivers

  3. Modem Pools, Digital Modems

     3.1 Analog Modem Pools, Multiport Modem Cards
     3.2 Digital Modems

  4. Serial Port and Modem Basics

     4.1 Modem Converts Digital to Analog (and conversely)
     4.2 What is a Serial Port ?
        4.2.1 Intro to Serial
        4.2.2 Pins and Wires
        4.2.3 Internal Modem Contains Serial Port
     4.3 IO Address & IRQ
     4.4 Names: ttyS0, ttyS1, etc.
     4.5 Interrupts
     4.6 Data Compression (by the Modem)
     4.7 Error Correction
     4.8 Data Flow (Speeds)
     4.9 Flow Control
        4.9.1 Example of Flow Control
        4.9.2 Hardware vs. Software Flow Control
        4.9.3 Symptoms of No Flow Control
        4.9.4 Modem-to-Modem Flow Control
     4.10 Data Flow Path; Buffers
     4.11 Modem Commands
     4.12 Serial Driver Module

  5. Configuring Overview

  6. Configuring the Serial Port Hardware and Driver (low-level)

     6.1 PCI Bus Support Underway
     6.2 Configuring Overview
     6.3 Common mistakes made re low-level configuring
     6.4 I/O Address & IRQ: Boot-time messages
     6.5 What is the current IO address and IRQ of my Serial Port ?
        6.5.1 What does the device driver think?
        6.5.2 What is set in my serial port hardware ?
        6.5.3 What is set in my PnP serial port hardware ?
     6.6 Choosing Serial IRQs
        6.6.1 IRQ 0 is not an IRQ
        6.6.2 Interrupt sharing and Kernels 2.2+
        6.6.3 What IRQs to choose?
     6.7 Choosing Addresses --Video card conflict with ttyS3
     6.8 Set IO Address & IRQ in the hardware (mostly for PnP)
        6.8.1 Using a PnP BIOS to I0-IRQ Configure
     6.9 Giving the IRQ and IO Address to Setserial

  7. Configuring the Serial Driver (high-level) "stty"

     7.1 Introduction
     7.2 Hardware flow control (RTS/CTS)
     7.3 Other Driver Settings (high level)

  8. Modem Configuration (excluding serial port)

     8.1 Finding Your Modem
     8.2 AT Commands
     8.3 Init Strings: Saving and Recalling
        8.3.1 Where is my "init string" so I can modify it ?
     8.4 Other AT Modem Commands
     8.5 Blacklisting
     8.6 What AT Commands are Now Set in my Modem?
     8.7 Modem States (or Modes)

  9. Serial Port Devices /dev/ttyS2, etc.

     9.1 Devfs (The new Device File System)
     9.2 Serial Port Device Names & Numbers
     9.3 Universal Serial Bus Ports
     9.4 Link ttySN to /dev/modem
     9.5 cua Device Obsolete

  10. Interesting Programs You Should Know About

     10.1 What is setserial ?
        10.1.1 Introduction
        10.1.2 Probing
        10.1.3 Boot-time Configuration
        10.1.4 Configuration Scripts/Files
        10.1.5 Edit a script (required prior to version 2.15)
        10.1.6 New configuration method using /etc/serial.conf
        10.1.7 IRQs
     10.2 What is isapnp ?
     10.3 What is wvdialconf ?
     10.4 What is stty ?

  11. Trying Out Your Modem (Dialing Out)

     11.1 Are You Ready to Dial Out ?
     11.2 Dialing Out with Minicom
     11.3 Dialing Out with Kermit

  12. Dial-In

     12.1 Dial-In Overview
     12.2 What Happens when Someone Dials In ?
     12.3 56k doesn't work
     12.4 Getty
        12.4.1 Introduction to Getty
        12.4.2 Getty "exits" after login (and can respawn)
        12.4.3 About mgetty
        12.4.4 About uugetty
        12.4.5 About getty_em
        12.4.6 About agetty
        12.4.7 About mingetty, and fbgetty
     12.5 Why "Manual" Answer is Best
     12.6 Ending a Dial-in Call
        12.6.1 Caller logs out
        12.6.2 When DTR drops (is negated)
        12.6.3 Caller hangs up
     12.7 Dial-in Modem Configuration
     12.8 Callback
     12.9 Voice Mail
     12.10 Simple Manual Dial-In
     12.11 Complex GUI Dial-In, VNC
     12.12 Interoperability with MS Windows

  13. Uugetty for Dial-In (from the old Serial-HOWTO)

     13.1 Installing getty_ps
     13.2 Setting up uugetty
        13.2.1 Modern Modems
        13.2.2 Old slow modems
        13.2.3 Login Banner
     13.3 Customizing uugetty

  14. What Speed Should I Use with My Modem?

     14.1 Speed and Data Compression
     14.2 Where do I Set Speed ?
     14.3 Can't Set a High Enough Speed
        14.3.1 How speed is set in hardware: the divisor and baud_base
        14.3.2 Work-arounds for setting speed
        14.3.3 Crystal frequency is not baud_base
     14.4 Speed Table

  15. Communications Programs And Utilities

     15.1 Minicom vs. Kermit
     15.2 List of Communication Software
        15.2.1 Least Popular Dialout
        15.2.2 Most Popular Dialout
        15.2.3 Fax
        15.2.4 Voicemail Software
        15.2.5 Dial-in (uses getty)
        15.2.6 Other
     15.3 SLiRP and term
     15.4 MS Windows

  16. Troubleshooting

     16.1 My Modem is Physically There but Can't be Found
        16.1.1 No response to AT
     16.2 "Modem is busy"
     16.3 I can't get near 56k on my 56k modem
     16.4 Uploading (downloading) files is broken/slow
     16.5 For Dial-in I Keep Getting "line NNN of inittab invalid"
     16.6 I Keep Getting: ``Id "S3" respawning too fast: disabled for 5 minutes''
     16.7 My Modem is Hosed after Someone Hangs Up, or uugetty doesn't respawn
     16.8 uugetty Still Doesn't Work
     16.9 (The following subsections are in both the Serial and Modem HOWTOs)
     16.10 My Serial Port is Physically There but Can't be Found
     16.11 Extremely Slow: Text appears on the screen slowly after long delays
     16.12 Somewhat Slow: I expected it to be a few times faster
     16.13 The Startup Screen Show Wrong IRQs for the Serial Ports.
     16.14 "Cannot open /dev/ttyS?: Permission denied"
     16.15 "Operation not supported by device" for ttyS?
     16.16 "Cannot create lockfile. Sorry"
     16.17 "Device /dev/ttyS? is locked."
     16.18 "/dev/tty? Device or resource busy"
     16.19 "Input/output error" from setserial or stty
     16.20 Overrun errors on serial port
     16.21 Modem doesn't pick up incoming calls
     16.22 Port get characters only sporadically
     16.23 Troubleshooting Tools

  17. Flash Upgrades

  18. Other Sources of Information

     18.1 Misc
     18.2 Books
     18.3 HOWTOs
     18.4 Usenet newsgroups
     18.5 Web Sites

  19. Appendix A:  How Analog Modems Work (technical) (unfinished)

     19.1 Modulation Details
        19.1.1 Intro to Modulation
        19.1.2 Frequency Modulation
        19.1.3 Amplitude Modulation
        19.1.4 Phase Modulation
        19.1.5 Combination Modulation
     19.2 56k Modems (v.90)
     19.3 Full Duplex on One Circuit
     19.4 Echo Cancellation

  20. Appendix B: Digital Modem Signal Processing (not done)

  21. Appendix C: "baud" vs. "bps"

     21.1 A simple example
     21.2 Real examples

  22. Appendix D: Terminal Server Connection

  23. Appendix E:  Other Types of Modems

     23.1 Digital-to-Digital "Modems"
     23.2 ISDN "Modems"
     23.3 Digital Subscriber Line (DSL)
     23.4 56k Digital-Modems
     23.5 Leased Line Modems

  24. Appendix F: Fax pixels (dots)

  25. Appendix G: Antique Modems

     25.1 Autobauding
        25.1.1 Various meanings
        25.1.2 Modem-to-modem speed
        25.1.3 Modem-to-serial_port speed
     25.2 Before AT Commands
     25.3 Data Compression and Error Correction
     25.4 Obsolete CCITT (ITU) and Bell Protocols
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