Modem-HOWTO

David S.Lawyer mailto:dave at lafn.org

1. Introduction

• 1.1 DSL, Cable, and ISDN Modems in other HOWTOs
• 1.2 Also not well 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
• 1.10 dev/modem

2. Modems for a Linux PC

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

3. Modem Pools, RAS

• 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 What Bus is my Serial Port On?
• 6.2 IO & IRQ Overview
• 6.3 PCI Bus Support
• 6.4 Common mistakes made re low-level configuring
• 6.5 IRQ & IO Address Must be Correct
• 6.6 What is the IO Address and IRQ per the driver ?
• 6.7 What is the IO Address & IRQ of my Serial Port Hardware?
• 6.8 Choosing Serial IRQs
• 6.9 Choosing Addresses --Video card conflict with ttyS3
• 6.10 Set IO Address & IRQ in the hardware (mostly for PnP)
• 6.11 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/ttyS4, (or /dev/ttys/4) etc.

• 9.1 Serial Port Names: ttyS4, etc
• 9.2 The PCI Bus
• 9.3 Serial Port Device Names & Numbers
• 9.4 More on Serial Port Names
• 9.5 USB (Universal Serial Bus) Serial Ports
• 9.6 Link ttySN to /dev/modem
• 9.7 Devfs (The Improved but Obsolete Device File System)
• 9.8 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 Distinctive Ring
• 12.11 Voice Mail
• 12.12 Simple Manual Dial-In
• 12.13 Complex GUI Dial-In, VNC
• 12.14 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. ISDN "Modems"

• 17.1 External ISDN "Modems"
• 17.2 Internal ISDN "Modems"

18. Troubleshooting

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

19. Flash Upgrades

20. Other Sources of Information

• 20.1 Misc
• 20.2 Books
• 20.3 HOWTOs
• 20.4 Usenet newsgroups
• 20.5 Old Modem Database on Internet
• 20.6 Other Web Sites

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

• 21.1 Modulation Details
• 21.2 56k Modems (V.90, V.92)
• 21.3 Full Duplex on One Circuit
• 21.4 Echo Cancellation

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

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

• 23.1 A simple example
• 23.2 Real examples

24. Appendix D: Terminal Server Connection

25. Appendix E: Cable and DSL modems

• 25.1 Introduction
• 25.2 Digital Subscriber Line (DSL)
• 25.3 Cable Modems

26. Appendix F: Connecting 2 Modems Directly Back-to-Back (Leased Lines).

27. Appendix G: Fax pixels (dots)

28. Appendix H: Stty Hanging Problem (prior to 2000)

29. Appendix G: Antique Modems

• 29.1 Introduction
• 29.2 Historical Modem Protocols
• 29.3 Historical Overview
• 29.4 Proprietary protocols, etc.
• 29.5 Autobauding
• 29.6 Modem-to-modem Speed
• 29.7 Modem-to-serial_port Speed
• 29.8 Before AT Commands
• 29.9 Acoustic-Coupling
• 29.10 Data Compression and Error Correction
• 29.11 Historical Bibliography