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Modem-HOWTO

David S.Lawyer mailto:dave@lafn.org

v0.31, November 2003

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Help with selecting, connecting, configuring, trouble-shooting, and understanding analog modems for a PC. Limited coverage of V.90 digital modems.

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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
• 1.4 Contacting the Author
• 1.5 New Versions of this HOWTO
• 1.6 New in Recent Versions
• 1.7 What is a Modem ?
• 1.8 Does My Computer Contain an Internal Modem ?
• 1.9 Quick Install

2. Modems for a Linux PC

• 2.1 External vs. Internal
• 2.2 Is a Driver Needed ?
• 2.3 External Modems
• 2.4 Internal Modems
• 2.5 Software-based Modems (winmodems, linmodems)
• 2.6 PCI Modems
• 2.7 AMR Modems
• 2.8 USB Modems
• 2.9 Which Internal Modems might not work with Linux

3. Modem Pools

• 3.1 Introduction
• 3.2 Analog Modem Pools, Multi-modem Cards
• 3.3 Digital Modems, RAS

4. Serial Port and Modem Basics

• 4.1 Modem Converts Digital to Analog (and conversely)
• 4.2 What is a 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
• 4.10 Data Flow Path; Buffers
• 4.11 Modem Commands
• 4.12 Serial Driver Module

5. Configuring Overview

6. Locating the Serial Port: IO address, IRQs

• 6.1 IO & IRQ Overview
• 6.2 PCI Bus Support
• 6.3 Common mistakes made re low-level configuring
• 6.4 IRQ & IO Address Must be Correct
• 6.5 What is the IO Address and IRQ per the driver ?
• 6.6 What is the IO Address & IRQ of my Serial Port Hardware?
• 6.7 Choosing Serial IRQs
• 6.8 Choosing Addresses --Video card conflict with ttyS3
• 6.9 Set IO Address & IRQ in the hardware (mostly for PnP)
• 6.10 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 Speed Settings
• 7.4 Ignore CD Setting: clocal
• 7.5 What is stty ?

8. Modem Configuration (excluding serial port)

• 8.1 Finding Your Modem
• 8.2 AT Commands
• 8.3 Init Strings: Saving and Recalling
• 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, (or /dev/ttys/2) etc.

• 9.1 Devfs (The new Device File System)
• 9.2 Serial Port Device Names & Numbers
• 9.3 USB (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 ?
• 10.2 What is isapnp ?
• 10.3 What is wvdialconf ?

11. Trying Out Your Modem (Dialing Out)

• 11.1 Are You Ready to Dial Out ?
• 11.2 Dialing Out with wvdial
• 11.3 Dialing Out with Minicom
• 11.4 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 for Dialin
• 12.4 Getty
• 12.5 Why "Manual" Answer is Best
• 12.6 Dialing Out while Waiting for an Incoming Call
• 12.7 Ending a Dial-in Call
• 12.8 Dial-in Modem Configuration
• 12.9 Callback
• 12.10 Voice Mail
• 12.11 Simple Manual Dial-In
• 12.12 Complex GUI Dial-In, VNC
• 12.13 Interoperability with MS Windows

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

• 13.1 Installing getty_ps
• 13.2 Setting up uugetty
• 13.3 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
• 14.4 Speed Table

15. Communications Programs And Utilities

• 15.1 Minicom vs. Kermit
• 15.2 List of Communication Software
• 15.3 SLiRP and term
• 15.4 MS Windows

16. Two Modems (Modem Doubling)

• 16.1 Introduction
• 16.2 Modem Bonding

17. Troubleshooting

• 17.1 My Modem is Physically There but Can't be Found
• 17.2 "Modem is busy"
• 17.3 "You are already online! Hang up first." (from minicom)
• 17.4 I can't get near 56k on my 56k modem
• 17.5 Uploading (downloading) files is broken/slow
• 17.6 For Dial-in I Keep Getting "line NNN of inittab invalid"
• 17.7 I Keep Getting: ``Id "S3" respawning too fast: disabled for 5 minutes''
• 17.8 My Modem is Hosed after Someone Hangs Up, or uugetty doesn't respawn
• 17.9 NO DIALTONE
• 17.10 NO CARRIER
• 17.11 uugetty Still Doesn't Work
• 17.12 (The following subsections are in both the Serial and Modem HOWTOs)
• 17.13 My Serial Port is Physically There but Can't be Found
• 17.14 Extremely Slow: Text appears on the screen slowly after long delays
• 17.15 Somewhat Slow: I expected it to be a few times faster
• 17.16 The Startup Screen Show Wrong IRQs for the Serial Ports.
• 17.17 "Cannot open /dev/ttyS?: Permission denied"
• 17.18 "Operation not supported by device" for ttyS?
• 17.19 "Cannot create lockfile. Sorry"
• 17.20 "Device /dev/ttyS? is locked."
• 17.21 "/dev/tty? Device or resource busy"
• 17.22 "Input/output error" from setserial, stty, pppd, etc.
• 17.23 "LSR safety check engaged"
• 17.24 Overrun errors on serial port
• 17.25 Modem doesn't pick up incoming calls
• 17.26 Port gets characters only sporadically
• 17.27 Troubleshooting Tools

18. Flash Upgrades

19. Other Sources of Information

• 19.1 Misc
• 19.2 Books
• 19.3 HOWTOs
• 19.4 Usenet newsgroups
• 19.5 Web Sites

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

• 20.1 Modulation Details
• 20.2 56k Modems (V.90, V.92)
• 20.3 Full Duplex on One Circuit
• 20.4 Echo Cancellation

21. Appendix B: Analog Voice Infeasible Over Non-Voice Modem

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

• 22.1 A simple example
• 22.2 Real examples

23. Appendix D: Terminal Server Connection

24. Appendix E: Digital Modems: ISDN, DSL, RAS

• 24.1 Introduction
• 24.2 ISDN "Modems"
• 24.3 Digital Subscriber Line (DSL)
• 24.4 56k Digital-Modems

25. Appendix F: Leased Line Modems

26. Appendix G: Fax pixels (dots)

27. Appendix H: Antique Modems

• 27.1 Introduction
• 27.2 Old CCITT (ITU) and Bell Protocols
• 27.3 Historical Overview
• 27.4 Proprietary protocols, etc.
• 27.5 Autobauding
• 27.6 Modem-to-modem Speed
• 27.7 Modem-to-serial_port Speed
• 27.8 Before AT Commands
• 27.9 Acoustic-Coupling
• 27.10 Data Compression and Error Correction

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