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Modem-HOWTO
Modem-HOWTO
Table of Contents
Modem-HOWTO..............................................................................................................................................1 David S.Lawyer mailto:dave@lafn.org...................................................................................................1 1. Introduction..........................................................................................................................................1 2. Modems for a Linux PC .......................................................................................................................1 3. Modem Pools, RAS.............................................................................................................................1 4. Serial Port and Modem Basics.............................................................................................................1 5. Configuring Overview.........................................................................................................................2 6. Locating the Serial Port: IO address, IRQs ..........................................................................................2 7. Configuring the Serial Driver (high-level) "stty"...............................................................................2 8. Modem Configuration (excluding serial port).....................................................................................2 9. Serial Port Devices /dev/ttyS4, (or /dev/ttys/4) etc.............................................................................2 . 10. Interesting Programs You Should Know About................................................................................3 11. Trying Out Your Modem (Dialing Out)............................................................................................3 12. Dial-In...............................................................................................................................................3 13. Uugetty for Dial-In (from the old Serial-HOWTO)........................................................................3 . 14. What Speed Should I Use with My Modem?....................................................................................3 15. Communications Programs And Utilities..........................................................................................4 16. Two Modems (Modem Doubling).....................................................................................................4 17. ISDN "Modems"................................................................................................................................4 18. Troubleshooting.................................................................................................................................4 19. Flash Upgrades ...................................................................................................................................5 20. Other Sources of Information............................................................................................................5 21. Appendix A: How Analog Modems Work (technical) (unfinished).................................................5 22. Appendix B: Analog Voice Infeasible Over Non-Voice Modem.....................................................5 23. Appendix C: "baud" vs. "bps" ............................................................................................................5 24. Appendix D: Terminal Server Connection........................................................................................5 25. Appendix E: Cable and DSL modems...............................................................................................5 26. Appendix F: Connecting 2 Modems Directly Back-to-Back (Leased Lines)..................................5 27. Appendix G: Fax pixels (dots)...........................................................................................................5 28. Appendix H: Stty Hanging Problem (prior to 2000).........................................................................5 29. Appendix G: Antique Modems..........................................................................................................6 1. Introduction..........................................................................................................................................6 1.1 DSL, Cable, and ISDN Modems in other HOWTOs.........................................................................6 1.2 Also not well covered: PCMCIA Modems, PPP...............................................................................6 1.3 Copyright, Disclaimer, Trademarks, & Credits.................................................................................6 Copyright...........................................................................................................................................6 Disclaimer.........................................................................................................................................7 Trademarks........................................................................................................................................7 Credits...............................................................................................................................................7 1.4 Contacting the Author........................................................................................................................7 1.5 New Versions of this HOWTO.........................................................................................................8 1.6 New in Recent Versions .....................................................................................................................8 1.7 What is a Modem ?...........................................................................................................................8 1.8 Does My Computer Contain an Internal Modem ? ............................................................................9 1.9 Quick Install......................................................................................................................................9 Very Quick Install.............................................................................................................................9 Will my modem work under Linux?.................................................................................................9 External Serial Modem Install ..........................................................................................................9 . i
Modem-HOWTO
Table of Contents
Modem-HOWTO Internal Modems (ISA, PCI and AMR)..........................................................................................10 Internal Modems: Manual configuration .........................................................................................10 Old ISA Modems .............................................................................................................................10 Both PCI and ISA: Use setserial to tell the serial driver.................................................................10 Use MS Windows to set the BIOS (A last resort method)..............................................................11 All Modems....................................................................................................................................11 1.10 dev/modem .....................................................................................................................................11 2. Modems for a Linux PC .....................................................................................................................11 2.1 Many Winmodems Will Not Work with Linux...............................................................................11 2.2 External vs. Internal........................................................................................................................12 2.3 Is a Driver Needed ?........................................................................................................................12 2.4 External Modems.............................................................................................................................12 Do they all work under Linux? ........................................................................................................12 PnP External Modems.....................................................................................................................13 Cabling & Installation.....................................................................................................................13 What the Lights (LED's) Mean (for some external modems).........................................................13 2.5 Internal Modems..............................................................................................................................13 2.6 Software-based Modems (winmodems, linmodems) .....................................................................14 Introduction to software modems (winmodems)............................................................................14 . Linmodems......................................................................................................................................14 Linmodem sites and documentation................................................................................................15 Software-based modem types.........................................................................................................15 Is this modem a software modem?..................................................................................................16 Should I get a software modem?.....................................................................................................16 2.7 PCI Modems...................................................................................................................................17 2.8 AMR Modems.................................................................................................................................17 2.9 USB Modems..................................................................................................................................17 2.10 Which Internal Modems might not work with Linux...................................................................17 MWave and some DSP Modems ....................................................................................................17 Old Rockwell (RPI) Drivers...........................................................................................................18 3. Modem Pools, RAS...........................................................................................................................18 3.1 Introduction......................................................................................................................................18 3.2 Analog Modem Pools, Multi-modem Cards...................................................................................19 3.3 Digital Modems, RAS .....................................................................................................................20 4. Serial Port and Modem Basics..........................................................................................................20 4.1 Modem Converts Digital to Analog (and conversely).....................................................................21 4.2 What is a Serial Port ? ......................................................................................................................21 Intro to Serial...................................................................................................................................21 Pins and Wires.................................................................................................................................21 Internal Modem Contains Serial Port..............................................................................................22 4.3 IO Address & IRQ...........................................................................................................................22 4.4 Names: ttyS0, ttyS1, etc...................................................................................................................22 4.5 Interrupts.........................................................................................................................................23 4.6 Data Compression (by the Modem).................................................................................................24 4.7 Error Correction...............................................................................................................................24 4.8 Data Flow (Speeds)..........................................................................................................................24 4.9 Flow Control...................................................................................................................................25 ii
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Modem-HOWTO Example of Flow Control................................................................................................................25 Hardware vs. Software Flow Control..............................................................................................26 Symptoms of No Flow Control.......................................................................................................27 Modem-to-Modem Flow Control.................................................................................................27 4.10 Data Flow Path; Buffers .................................................................................................................27 4.11 Modem Commands........................................................................................................................28 4.12 Serial Driver Module.....................................................................................................................28 5. Configuring Overview.......................................................................................................................29 6. Locating the Serial Port: IO address, IRQs .......................................................................................29 6.1 What Bus is my Serial Port On?......................................................................................................29 6.2 IO & IRQ Overview .........................................................................................................................29 6.3 PCI Bus Support.............................................................................................................................31 Introduction.....................................................................................................................................31 More info on PCI .............................................................................................................................31 6.4 Common mistakes made re low-level configuring.........................................................................32 6.5 IRQ & IO Address Must be Correct...............................................................................................32 6.6 What is the IO Address and IRQ per the driver ?............................................................................32 Introduction.....................................................................................................................................32 I/O Address & IRQ: Boot-time messages.....................................................................................32 The /proc directory and setserial....................................................................................................34 6.7 What is the IO Address & IRQ of my Serial Port Hardware?........................................................34 Introduction.....................................................................................................................................34 PCI: What IOs and IRQs have been set? ........................................................................................34 PCI: Enabling a disabled port ........................................................................................................35 . ISA PnP ports.................................................................................................................................35 Finding a port that is not disabled (ISA, PCI, PnP, non-PnP) ........................................................35 Exploring via MS Windows (a last resort)......................................................................................36 6.8 Choosing Serial IRQs.....................................................................................................................36 IRQ 0 is not an IRQ .........................................................................................................................36 Interrupt sharing, Kernels 2.2+......................................................................................................36 What IRQs to choose?.....................................................................................................................36 6.9 Choosing Addresses --Video card conflict with ttyS3..................................................................37 6.10 Set IO Address & IRQ in the hardware (mostly for PnP)............................................................38 . Using a PnP BIOS to I0-IRQ Configure.......................................................................................38 6.11 Giving the IRQ and IO Address to Setserial.................................................................................39 . 7. Configuring the Serial Driver (high-level) "stty"............................................................................39 7.1 Introduction......................................................................................................................................39 7.2 Hardware flow control (RTS/CTS) ..................................................................................................39 7.3 Speed Settings..................................................................................................................................40 7.4 Ignore CD Setting: clocal................................................................................................................40 . 7.5 What is stty ? ...................................................................................................................................40 8. Modem Configuration (excluding serial port)..................................................................................40 8.1 Finding Your Modem......................................................................................................................40 8.2 AT Commands.................................................................................................................................41 8.3 Init Strings: Saving and Recalling..................................................................................................41 Where is my "init string" so I can modify it ?.................................................................................42 8.4 Other AT Modem Commands........................................................................................................43 iii
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Modem-HOWTO 8.5 Blacklisting......................................................................................................................................43 8.6 What AT Commands are Now Set in my Modem?.........................................................................43 8.7 Modem States (or Modes) ................................................................................................................44 9. Serial Port Devices /dev/ttyS4, (or /dev/ttys/4) etc..........................................................................44 . 9.1 Serial Port Names: ttyS4, etc...........................................................................................................44 9.2 The PCI Bus.....................................................................................................................................44 9.3 Serial Port Device Names & Numbers............................................................................................45 9.4 More on Serial Port Names.............................................................................................................45 9.5 USB (Universal Serial Bus) Serial Ports.........................................................................................45 9.6 Link ttySN to /dev/modem..............................................................................................................45 9.7 Devfs (The Improved but Obsolete Device File System)................................................................45 9.8 cua Device Obsolete.......................................................................................................................46 10. Interesting Programs You Should Know About..............................................................................47 10.1 What is setserial ?.........................................................................................................................47 Setserial problems with linmodems, laptops...................................................................................47 Introduction.....................................................................................................................................47 Serial module unload.......................................................................................................................48 Giving the setserial command.........................................................................................................48 Configuration file............................................................................................................................49 Probing...........................................................................................................................................49 Boot-time Configuration...............................................................................................................50 Edit a script (required prior to version 2.15)..................................................................................51 Configuration method using /etc/serial.conf, etc...........................................................................51 . IRQs .................................................................................................................................................52 Laptops: PCMCIA ..........................................................................................................................53 10.2 What is isapnp ?.............................................................................................................................53 10.3 What is wvdialconf ?....................................................................................................................53 11. Trying Out Your Modem (Dialing Out).........................................................................................53 11.1 Are You Ready to Dial Out ? .........................................................................................................53 11.2 Dialing Out with wvdial...............................................................................................................54 11.3 Dialing Out with Minicom............................................................................................................54 11.4 Dialing Out with Kermit...............................................................................................................55 12. Dial-In............................................................................................................................................56 12.1 Dial-In Overview..........................................................................................................................56 12.2 What Happens when Someone Dials In ?......................................................................................56 12.3 56k Doesn't Work for Dialin ..........................................................................................................57 12.4 Getty ..............................................................................................................................................58 Introduction to Getty.......................................................................................................................58 How getty respawns........................................................................................................................58 About mgetty..................................................................................................................................59 About uugetty.................................................................................................................................59 About getty_em..............................................................................................................................59 About agetty...................................................................................................................................59 About mingetty, and fbgetty ............................................................................................................60 12.5 Why "Manual" Answer is Best......................................................................................................60 12.6 Dialing Out while Waiting for an Incoming Call.........................................................................60 12.7 Ending a Dial-in Call...................................................................................................................61 iv
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Modem-HOWTO Caller logs out.................................................................................................................................61 When DTR drops (is negated).........................................................................................................61 Caller hangs up...............................................................................................................................62 12.8 Dial-in Modem Configuration.....................................................................................................62 12.9 Callback.........................................................................................................................................63 12.10 Distinctive Ring...........................................................................................................................63 12.11 Voice Mail..................................................................................................................................64 12.12 Simple Manual Dial-In..............................................................................................................64 12.13 Complex GUI Dial-In, VNC.......................................................................................................64 12.14 Interoperability with MS Windows.............................................................................................65 13. Uugetty for Dial-In (from the old Serial-HOWTO).....................................................................65 . 13.1 Installing getty_ps..........................................................................................................................66 13.2 Setting up uugetty..........................................................................................................................66 Modern Modems.............................................................................................................................66 Old slow modems............................................................................................................................67 Login Banner...................................................................................................................................67 13.3 Customizing uugetty......................................................................................................................67 14. What Speed Should I Use with My Modem?.................................................................................68 14.1 Speed and Data Compression........................................................................................................69 14.2 Where do I Set Speed ?..................................................................................................................69 14.3 Can't Set a High Enough Speed....................................................................................................69 Speeds over 115.2kbps....................................................................................................................69 How speed is set in hardware: the divisor and baud_base.............................................................70 Setting the divisor, speed accounting..............................................................................................70 Crystal frequency is higher than baud_base....................................................................................70 14.4 Speed Table ...................................................................................................................................71 15. Communications Programs And Utilities.......................................................................................71 15.1 Minicom vs. Kermit.......................................................................................................................71 15.2 List of Communication Software...................................................................................................72 Least Popular Dialout......................................................................................................................72 Most Popular Dialout......................................................................................................................72 Fax..................................................................................................................................................72 Voicemail Software........................................................................................................................72 Dial-in (uses getty).........................................................................................................................72 Network Connection ........................................................................................................................73 Other................................................................................................................................................73 15.3 SLiRP and term.............................................................................................................................73 15.4 MS Windows.................................................................................................................................73 16. Two Modems (Modem Doubling)...................................................................................................74 16.1 Introduction....................................................................................................................................74 16.2 Modem Bonding............................................................................................................................74 EQL.................................................................................................................................................74 Multilink..........................................................................................................................................74 17. ISDN "Modems"..............................................................................................................................74 17.1 External ISDN "Modems".............................................................................................................74 17.2 Internal ISDN "Modems"..............................................................................................................75 18. Troubleshooting..............................................................................................................................75 v
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Modem-HOWTO 18.1 My Modem is Physically There but Can't be Found....................................................................75 Case 1: Winmodem........................................................................................................................75 Cases 2-3........................................................................................................................................75 Case 4: Wrong ttySx number.........................................................................................................76 wvdial.............................................................................................................................................76 minicom (test modem)...................................................................................................................76 . 18.2 "Modem is busy" ............................................................................................................................76 18.3 "You are already online! Hang up first." (from minicom) ............................................................77 18.4 I can't get near 56k on my 56k modem..........................................................................................77 18.5 Uploading (downloading) files is broken/slow..............................................................................77 18.6 For Dial-in I Keep Getting "line NNN of inittab invalid"............................................................77 18.7 I Keep Getting: ``Id "S4" respawning too fast: disabled for 5 minutes''.......................................78 . 18.8 Dial-in: When remote user hangs up, getty doesn't respawn........................................................78 18.9 NO DIALTONE .............................................................................................................................78 18.10 NO CARRIER.............................................................................................................................78 18.11 uugetty Still Doesn't Work ..........................................................................................................79 18.12 (The following subsections are in both the Serial and Modem HOWTOs) .................................79 18.13 Serial Port Can't be Found..........................................................................................................79 Scanning/probing legacy ports........................................................................................................80 18.14 Linux Creates an Interrupt Conflict (your PC has an ISA slot)...................................................80 18.15 Extremely Slow: Text appears on the screen slowly after long delays .......................................80 18.16 Somewhat Slow: I expected it to be a few times faster...............................................................81 18.17 The Startup Screen Shows Wrong IRQs for the Serial Ports ......................................................81 18.18 "Cannot open /dev/ttyS?: Device or resource busy.....................................................................81 18.19 "Cannot open /dev/ttyS?: Permission denied".............................................................................81 18.20 "Cannot open /dev/ttyS?" .............................................................................................................82 18.21 "Operation not supported by device" for ttyS?............................................................................82 18.22 "Cannot create lockfile. Sorry"...................................................................................................82 18.23 "Device /dev/ttyS? is locked.".....................................................................................................82 18.24 "/dev/tty? Device or resource busy"...........................................................................................83 18.25 "Input/output error" from setserial, stty, pppd, etc......................................................................84 18.26 "LSR safety check engaged" ........................................................................................................84 18.27 Overrun errors on serial port........................................................................................................84 18.28 Modem doesn't pick up incoming calls ........................................................................................84 18.29 Port gets characters only sporadically ..........................................................................................84 18.30 Troubleshooting Tools.................................................................................................................84 19. Flash Upgrades .................................................................................................................................85 20. Other Sources of Information..........................................................................................................85 20.1 Misc...............................................................................................................................................86 20.2 Books.............................................................................................................................................86 20.3 HOWTOs.......................................................................................................................................86 20.4 Usenet newsgroups........................................................................................................................86 20.5 Old Modem Database on Internet.................................................................................................87 20.6 Other Web Sites............................................................................................................................87 21. Appendix A: How Analog Modems Work (technical) (unfinished)..............................................87 21.1 Modulation Details.......................................................................................................................87 Intro to Modulation.........................................................................................................................87 vi
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Modem-HOWTO Frequency Modulation....................................................................................................................87 Amplitude Modulation....................................................................................................................88 Phase Modulation............................................................................................................................88 Combination Modulation...............................................................................................................88 21.2 56k Modems (V.90, V.92)............................................................................................................89 21.3 Full Duplex on One Circuit...........................................................................................................90 21.4 Echo Cancellation..........................................................................................................................91 22. Appendix B: Analog Voice Infeasible Over Non-Voice Modem...................................................91 23. Appendix C: "baud" vs. "bps" ..........................................................................................................91 23.1 A simple example..........................................................................................................................91 23.2 Real examples................................................................................................................................92 24. Appendix D: Terminal Server Connection......................................................................................92 25. Appendix E: Cable and DSL modems............................................................................................93 25.1 Introduction....................................................................................................................................93 25.2 Digital Subscriber Line (DSL).......................................................................................................93 25.3 Cable Modems...............................................................................................................................94 26. Appendix F: Connecting 2 Modems Directly Back-to-Back (Leased Lines)................................94 27. Appendix G: Fax pixels (dots).........................................................................................................94 28. Appendix H: Stty Hanging Problem (prior to 2000).......................................................................95 29. Appendix G: Antique Modems........................................................................................................95 29.1 Introduction....................................................................................................................................95 29.2 Historical Modem Protocols..........................................................................................................95 29.3 Historical Overview.......................................................................................................................95 Teletypes and dumb terminals .........................................................................................................96 PCs and BBSs .................................................................................................................................96 The Internet.....................................................................................................................................96 Speeds ..............................................................................................................................................96 29.4 Proprietary protocols, etc...............................................................................................................97 29.5 Autobauding ..................................................................................................................................97 29.6 Modem-to-modem Speed .............................................................................................................97 29.7 Modem-to-serial_port Speed ........................................................................................................98 Same speed required ........................................................................................................................98 Equalizing speed ..............................................................................................................................98 Use "CONNECT" message to set speed.........................................................................................98 Setting modem-to-modem speeds by the serial speed ...................................................................99 Manual bauding...............................................................................................................................99 Unsupported speeds .......................................................................................................................100 Modern modems, speed buffering.................................................................................................100 29.8 Before AT Commands.................................................................................................................100 29.9 Acoustic-Coupling......................................................................................................................100 29.10 Data Compression and Error Correction ....................................................................................100 29.11 Historical Bibliography ..............................................................................................................101
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Modem-HOWTO
David S.Lawyer mailto:[email protected]
v0.39, January 2007 Help with selecting, connecting, configuring, trouble-shooting, and understanding analog modems for a PC.
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. Modem-HOWTO 1
Modem-HOWTO · 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 4. Serial Port and Modem Basics 2
Modem-HOWTO · 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 9. Serial Port Devices /dev/ttyS4, (or /dev/ttys/4) etc. 3
Modem-HOWTO
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 15. Communications Programs And Utilities 4
Modem-HOWTO
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)
19. Flash Upgrades
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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
1. Introduction 1.1 DSL, Cable, and ISDN Modems in other HOWTOs
This HOWTO covers conventional analog modems for PCs on the PCI, USB, LPC, and ISA buses. USB and ISDN coverage is weak. For other types of modems see: · DSL-HOWTO · ADSL-Bandwidth-Management-HOWTO · Cable-Modems-HOWTO (same as Cable Modem Providers HOWTO) · SuSE ISDN Howto (not a LDP Howto) http://brenner.chemietechnik.uni-dortmund.de/doc/sdb/en/html/isdn.html · http://public.swbell.net/ISDN/overview.html tutorial on ISDN · ISDN docs in the kernel documentation subdirectory: "isdn". · http://www.isdn4linux.de · Appendix D: Other Types of Modems
1.2 Also not well covered: PCMCIA Modems, PPP
For modems on the PCMCIA bus see the PCMCIA-HOWTO: PCMCIA serial and modem devices. This HOWTO also doesn't cover the details of PPP (used to connect to the Internet via a modem) or communication programs. If you want to use a modem to connect to the Internet then you need to use a program that will automatically set up PPP for you (such as wvdial). More documentation on ppp should be found in /usr/doc/ppp, /usr/share/doc/ppp or the like.
1.3 Copyright, Disclaimer, Trademarks, & Credits
Copyright
Copyright (c) 1998-2005 by David S. Lawyer mailto:[email protected] Please freely copy and distribute (sell or give away) this document in any format. Send any corrections and comments to the document maintainer. You may create a derivative work and distribute it provided that you:
29. Appendix G: Antique Modems
6
Modem-HOWTO 1. If it's not a translation: Email a copy of your derivative work (in a format LDP accepts) to the author(s) and maintainer (could be the same person). If you don't get a response then email the LDP (Linux Documentation Project): [email protected]. 2. License the derivative work in the spirit of this license or use GPL. Include a copyright notice and at least a pointer to the license used. 3. Give due credit to previous authors and major contributors. If you're considering making a derived work other than a translation, it's requested that you discuss your plans with the current maintainer.
Disclaimer
While I haven't intentionally tried to mislead you, there are likely a number of errors in this document. Please let me know about them. Since this is free documentation, it should be obvious that I cannot be held legally responsible for any errors.
Trademarks.
Any brand names (starts with a capital letter such as MS Windows) should be assumed to be a trademark). Such trademarks belong to their respective owners. "Hayes" is a trademark of Microcomputer Products Inc. I use "winmodem" to mean any modem which originally required MS-Windows and not in the trademark sense. All other trademarks belong to their respective owners.
Credits
The following is only a rough approximation of how this this document was created in the year 2000: About 1/4 of the material here was lifted directly from Serial-HOWTO v. 1.11 (1997) by Greg Hankins. mailto:[email protected] (with his permission). About another 1/4 was taken from that Serial-HOWTO and revised. The remaining 1/2 is newly created by the new author: David S. Lawyer mailto:[email protected]. Since 2000 much more has been added by the current author so that little remains of the modem coverage in the old Serial-HOWTO.
1.4 Contacting the Author
Since I don't follow the many different brands/models of modems please don't email me with questions about them (or suggestions of which one to buy). If you are interested in a certain model (to find out if it works under Linux, etc.) see the huge list at Web Sites. Also, please don't ask me how to configure a modem unless you've looked over this HOWTO and still can't do it. I've no personal experience with software-based modems. Please let me know of any errors in facts, opinions, logic, spelling, grammar, clarity, links, etc. But first, if the date is over a month or two old, check to see that you have the latest version. Please send me any other info that you think belongs in this document.
Copyright
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1.5 New Versions of this HOWTO
New versions of this Modem-HOWTO should come out every few months. Your problem might be solved in the latest version. It will be available to browse and/or download at LDP mirror sites. For a list of such sites see: http://www.tldp.org/mirrors.html If you only want to quickly compare the date of this the version v0.39, January 2007 with the date of the latest version go to: http://www.tldp.org/HOWTO/Modem-HOWTO.html
1.6 New in Recent Versions
For a full revision history going back to the first version see the source file (in linuxdoc format) at http://cvsview.tldp.org/index.cgi/LDP/howto/linuxdoc/Modem-HOWTO.sgml. · v0.39 Jan. 2007 gromitkc url (modem list) seems to be no longer maintained. Redefined "antique modems" as all under 56k speed. setpci can't set IRQs. devfs is obsolete. vgetty supports ITU v.253 · v0.38 May 2005: Eliminated section on Digital Modems in appendix since it's already covered elsewhere. More on cable modems. ISDN serial modems. Troubleshooting: Can't find winmodems if no driver. · v0.37 Feb. 2005: For AMR, codec is on motherboard. Fixed a few typos. Better clarity for Dial-In. "NO CARRIER" likely not displayed when remote hangs up. · v0.36 Feb. 2005 Rewrote "Quick Install" oriented towards PCI. Some external RS-232 modems are winmodems. /dev/modem.
1.7 What is a Modem ?
A modem (or analog modem) is a device that lets one send digital signals over an ordinary telephone line not designed for digital signals. If telephone lines were all digital then you wouldn't need a modem. But sometimes, a substitute for an analog modem, connected to a digital phone line, is imprecisely called a "digital modem". A modem permits your computer to connect to and communicate with the rest of the world. When you use a modem, you normally use a communication program or web browser to utilize the modem and dial-out on a telephone line. Advanced modem users can set things up so that others may phone in to them and use the computer remotely. This is called "dial-in". Oversimplified, there are four basic types of analog modems for a PC: external serial (RS-232), USB (= external USB), internal, and built-in. The external serial and USB set on your desk outside the PC while the other two types are not visible since they're inside the PC. The external serial modem plugs into a connector on the back of the PC known as a "serial port". The USB modem plugs into a USB cable. See USB Modems. The internal modem is a card that is inserted inside the computer. The built-in modem is a chip on the motherboard used primarily in laptops. What is said in this HOWTO regarding internal modems will generally apply also to built-in modems. Internal modems are further subdivided into PCI, ISA, and AMR, depending on whether they are designed for the PCI or ISA bus, or for an AMR slot. For an external vs internal comparison see External vs. Internal. When you get an internal or built-in modem, you also get a dedicated serial port (which can only be used with the modem and not with anything else such as an external modem or console terminal). In Linux, the common serial ports are named ttyS0, ttyS1, etc. These ports usually corresponding respectively to COM1, COM2, etc. in Dos/Windows). But in special cases, the names are longer such as: ttySHCF0 is the 0th serial port for a type of winmodem (HCF = Host Controlled Family). New types of serial ports just add some more letters to ttyS.
1.5 New Versions of this HOWTO
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Modem-HOWTO See Modem & Serial Port Basics for more details on how modems and serial ports work. With a USB modem, the driver simulates a serial port at for example /dev/ttySHCFUSB. Modems usually include the ability to send Faxes (Fax Modems). See Fax for a list of fax software. "Voice" modems can work like an automatic answering machine and handle voicemail. See Voicemail Software. The v.92 protocol can put the modem "on hold" when someone makes an ordinary voice call to your telephone, provided that you have "call waiting" from your telephone company. Thus you can get a phone call while online. As of Jan. 2003 Linux doesn't seem to support it. If this is the latest version of this HOWTO, let me know about any Linux support for it. Some linmodem drivers may support it (but what if you have a hardware modem that doesn't use any linmodem driver?).
1.8 Does My Computer Contain an Internal Modem ?
Internal modems usually have a pair of modular telephone jacks on the back of the computer. They should be right next to each other and each one looks like a jack on the interior wall of a building where a telephone plugs in. One of the pair should be labeled "line" (or the like) which is where you plug in the telephone line. Network cards also have modular jacks, but they are seldom in pairs and are slightly wider since they normally have 8 pins. Internal DSL "modems" exist and also have modular telephone jacks, but I think they are not very common (most DSL modems are external) as of 2002.
1.9 Quick Install
Very Quick Install
If you think your modem will work under Linux and needs no special driver, then just physically install/connect it. Start you computer, watch the boot-time messages for Linux to find the modem. Note it's the serial port number such as ttyS2 (/dev/ttyS2). Connect a phone line to it and dial out with say wvdial (after configuring wvdial). If the above doesn't work, read on.
Will my modem work under Linux?
So called "winmodems" will work under Linux only if a driver for it exists and gets installed. In this case it's called a "linmodem" since it can be made to work under Linux. If it's made prior to 2004 see old modem list and Software-based Modems (winmodems). There's no point of installing a modem that will not work with Linux.
External Serial Modem Install
At one time (2002 ?) no external serial modem was a winmodem but that's no longer the case. With a straight-thru or modem cable, connect the modem to an unused serial port on the PC. Make sure you know the name of the serial port: in most cases COM1 is ttyS0, COM2 is ttyS1, etc. You may need to check the BIOS setup menu to determine this. Plug in the power cord to provide power to the modem. See All Modems for further instructions.
1.7 What is a Modem ?
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Internal Modems (ISA, PCI and AMR)
If the modem is both PnP and directly supported by the serial driver (kernel 2.4 +) or by a winmodem driver that you've installed, then there is no configuring for you to do since the driver should configure it. To physically install a modem card, remove the cover of the PC by /removing some screws. Find a matching vacant slot for the card next to the other adapter cards. Before inserting the card in the slot, remove a small cover plate on the back of the PC so that the telephone jacks on the card will be accessible from the rear of the PC. Then carefully align the card with the slot and push the card all the way down into the slot. Attach the card with a mounting screw (usually 3mm, .5mm pitch --don't use the wrong size). You may watch the boot-time messages to see if your modem is detected. Use "dmesg" to see them or shift-page-up to scroll the screen back after they have flashed by.
Internal Modems: Manual configuration
Normally, you don't need to do this manual configuration since the modem's serial port may be detected and assigned a port at boot-time. For example: ttyS14 at I/O 0x6450 (IRQ = 10). Otherwise (or if there is some special reason to change the configuration) then you need to configure it yourself (or perhaps update your kernel to increases the likelihood that the modem gets detected). If your modem has no ttyS number assigned to it, it can't be used until it gets a ttyS number (like ttyS10). It thus can't be detected by application programs such as dialers or minicom. But it might be found by using say "lspci -v" if it's on the PCI bus. Finding a lost modem may not be easy and you may need to read a lot more of this HOWTO. Once found, you need to use the "setserial" program to manually assign it to an available ttyS? port of your choice . For this you need to know both it's IO address (such as 0x6450) and its IRQ (such as 10). In the worst case, the modem has been disabled by a failing to be detected and enabled by the BIOS (or Linux) and doesn't have any IO address nor IRQ number. But you may still be able to find it. Older modems could be disabled by a jumper on the card or in rare cases by MS software. You may have some choice of IRQs and IO addresses (including the case where you are able to change what the BIOS has set). See Choosing Serial IRQs and Choosing Addresses.
Old ISA Modems
ISA modems normally use ttyS0 - ttyS3. For old modems with jumpers look at the modem manual or look for printing on the modem card that tells you what the jumpers do. They have standard IO addresses corresponding to the ttySx.