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Modem-HOWTO
David S.Lawyer
mailto:dave@lafn.org
v0.27, May 2003
Help with selecting, connecting, configuring, trouble-shooting, and understanding analog modems for a PC. Limited coverage of V.90 digital modems.
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 get 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: (Reserved for future use)
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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