The Linux Modem HOWTO

David S.Lawyer mailto:bf347@lafn.org Contains much info from Serial-HOWTO by Greg Hankins

1. Introduction

• 1.1 Copyright, Trademarks, Disclaimer, & Credits
• 1.2 Future Plans: You Can Help
• 1.3 New Versions of this HOWTO
• 1.4 What is a Modem ?
• 1.5 Quick Install

2. Serial Port & Modem Basics

• 2.1 Modem Converts Digital to Analog (and conversely)
• 2.2 What is a Serial Port ?
• 2.3 Address & IRQ
• 2.4 Interrupts
• 2.5 Data Compression (by the Modem)
• 2.6 Error Correction
• 2.7 Data Flow (Speeds)
• 2.8 Flow Control
• 2.9 Data Flow Path; Buffers
• 2.10 Complex Flow Control Example
• 2.11 Modem Commands

3. Configuring Modems

• 3.1 Configuring Overview
• 3.2 Configuring the IRQ and IO-Address of the Serial Port (Overview)
• 3.3 What is the current I/O address and IRQ of my Serial Port ?
• 3.4 Other Configuring
• 3.5 Modem Configuration

4. Modems for a Linux PC

• 4.1 External vs. Internal
• 4.2 External Modems
• 4.3 Internal Modems
• 4.4 Internal Modems You Must Avoid: Winmodems, etc.
• 4.5 Which Internal Modems are Best to Avoid ?

5. Serial Port Devices: /dev/ttySN

• 5.1 Serial Port Device Numbers
• 5.2 Creating Devices In /dev
• 5.3 Link ttySN to /dev/modem ?
• 5.4 The cua Device

6. Interesting Programs You Should Know About

• 6.1 What is getty?
• 6.2 What is setserial ?
• 6.3 What is isapnp ?

7. Trying Out Your Modem (Dialing Out)

• 7.1 Are You Ready to Dial Out ?
• 7.2 Dialing Out with Minicom
• 7.3 Dialing Out with Kermit

8. Uugetty (from the old Serial-HOWTO)

• 8.1 Installing getty_ps
• 8.2 Setting up uugetty
• 8.3 Customizing uugetty

9. What Speed Should I Use with My Modem?

• 9.1 Speed and Data Compression
• 9.2 Where do I Set Speed ?
• 9.3 Can't Set a High Enough Speed
• 9.4 Speed Table

10. Communications Programs And Utilities

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

12. Troubleshooting

• 12.1 My Modem Is Physically There but Can't Be Found
• 12.2 For Dial-in: I Keep Getting ``line NNN of inittab invalid''
• 12.3 When I Try To Dial Out, It Says ``/dev/ttySN: Device or resource busy''
• 12.4 I Keep Getting ``Getty respawning too fast: disabled for 5 minutes''
• 12.5 Serial Devices Are Slow, Or They Can Only Send In One Direction
• 12.6 My Modem Is Hosed After Someone Hangs Up, Or uugetty doesn't respawn
• 12.7 uugetty Still Doesn't Work

13. Other Sources Of Information

• 13.1 Misc
• 13.2 HOWTOs
• 13.3 Usenet newsgroups:
• 13.4 Web Sites

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

• 14.1 Modulation Details

15. Appendix B: ``baud'' Vs. ``bps''

• 15.1 A simple example
• 15.2 Real examples

16. Appendix C: Terminal Server Connection

17. Appendix D: Other Types of Modems

• 17.1 Digital-to-Digital "Modems"
• 17.2 ISDN "Modems"
• 17.3 Digital Subscriber Line (DSL)