The Linux Modem-HOWTO

David S.Lawyer mailto:dave@lafn.org

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 What is a Modem ?
• 1.7 Quick Install

2. Modem & Serial Port Basics

• 2.1 Modem Converts Digital to Analog (and conversely)
• 2.2 What is a Serial Port ?
• 2.3 IO Address & IRQ
• 2.4 Names: ttyS0, ttyS1, etc.
• 2.5 Interrupts
• 2.6 Data Compression (by the Modem)
• 2.7 Error Correction
• 2.8 Data Flow (Speeds)
• 2.9 Flow Control
• 2.10 Data Flow Path; Buffers
• 2.11 Modem Commands
• 2.12 Serial Software: Device Driver Module

3. Configuring Modems (including the serial port)

• 3.1 Configuring Overview

4. Configuring the Serial Port

• 4.1 PCI Bus Not Yet Supported
• 4.2 Configuring Overview
• 4.3 Common mistakes made re low-level configuring
• 4.4 I/O Address & IRQ: Boot-time messages
• 4.5 What is the current IO address and IRQ of my Serial Port ?
• 4.6 Choosing Serial IRQs
• 4.7 Choosing Addresses --Video card conflict with ttyS3
• 4.8 Set IO Address & IRQ in the hardware (mostly for PnP)
• 4.9 Giving the IRQ and IO Address to Setserial
• 4.10 Other Configuring

5. Modem Configuration (excluding serial port)

• 5.1 AT Commands
• 5.2 Init Strings: Saving and Recalling
• 5.3 Other Modem Commands

6. Modems for a Linux PC

• 6.1 External vs. Internal
• 6.2 External Modems
• 6.3 Internal Modems
• 6.4 Internal Modems You Must Avoid (winmodems, etc.)
• 6.5 Which Internal Modems are Best to Avoid ?

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

• 7.1 Serial Port Device Names & Numbers
• 7.2 Link ttySN to /dev/modem ?
• 7.3 The cua Device

8. Interesting Programs You Should Know About

• 8.1 What is setserial ?
• 8.2 What is isapnp ?
• 8.3 What is wvdialconf ?
• 8.4 What is stty ?

9. Trying Out Your Modem (Dialing Out)

• 9.1 Are You Ready to Dial Out ?
• 9.2 Dialing Out with Minicom
• 9.3 Dialing Out with Kermit

10. Dial-In

• 10.1 Overview
• 10.2 Getty
• 10.3 What Happens when Someone Dials In ?
• 10.4 Why Manual Answer is Best
• 10.5 Callback
• 10.6 Voice Mail

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

• 11.1 Installing getty_ps
• 11.2 Setting up uugetty
• 11.3 Customizing uugetty

12. What Speed Should I Use with My Modem?

• 12.1 Speed and Data Compression
• 12.2 Where do I Set Speed ?
• 12.3 Can't Set a High Enough Speed
• 12.4 Speed Table

13. Communications Programs And Utilities

• 13.1 Minicom vs. Kermit
• 13.2 Lists of Programs
• 13.3 SLiRP and term

14. What Are UARTs? How Do They Affect Performance?

• 14.1 Introduction to UARTS
• 14.2 Two Types of UARTs
• 14.3 FIFOs
• 14.4 UART Model Numbers

15. Troubleshooting

• 15.1 I can't get 56K on my 56K modem
• 15.2 Uploading (downloading) files is broken/slow
• 15.3 For Dial-in I Keep Getting "line NNN of inittab invalid"
• 15.4 I Keep Getting: ``Id "S3" respawning too fast: disabled for 5 minutes''
• 15.5 My Modem is Hosed after Someone Hangs Up, or uugetty doesn't respawn
• 15.6 uugetty Still Doesn't Work
• 15.7 My Modem is Physically There but Can't be Found
• 15.8 The following subsections are in both the Serial and Modem HOWTOs:
• 15.9 My Serial Port is Physically There but Can't be Found
• 15.10 Extremely Slow: Text appears on the screen slowly after long delays
• 15.11 Somewhat Slow: I expected it to be 2-4 times faster
• 15.12 The Startup Screen Show Wrong IRQs for the Serial Ports.
• 15.13 "Cannot open /dev/ttyS?: Permission denied"
• 15.14 "Operation not supported by device" (error message) for ttySx
• 15.15 "Cannot create lockfile. Sorry" (error message)
• 15.16 "Device /dev/ttyS? is locked."
• 15.17 "/dev/ttySN: Device or resource busy"
• 15.18 Software which may help

16. Flash Upgrades

17. Other Sources of Information

• 17.1 Misc
• 17.2 Books
• 17.3 HOWTOs
• 17.4 Usenet newsgroups
• 17.5 Web Sites

18. Appendix A: How Modems Work (technical) (unfinished)

• 18.1 Modulation Details

19. Appendix B: "baud" vs. "bps"

• 19.1 A simple example
• 19.2 Real examples

20. Appendix C: Terminal Server Connection

21. Appendix D: Other Types of Modems

• 21.1 Digital-to-Digital "Modems"
• 21.2 ISDN "Modems"
• 21.3 Digital Subscriber Line (DSL)