What You Need to Know about Modems

May 31, 1992
Version 1.1

Copyright (c) 1991-92 Patrick Chen. All rights reserved.

DISTRIBUTION NOTICE: This document may be distributed by electronic bulletin boards and commercial on-line services. This document may not be edited or changed in any way for redistribution.
This article is Part One of a three-part book/report entitled "The Joy of Telecomputing." As a plain ASCII file, it cannot contain any of the illustrations and graphic elements provided in the printed version. For further information about "The Joy of Telecomputing," see Appendix C to G.

This article should be useful to anyone interested in high-speed modems (or 2400-bps modems with MNP5 or V.42bis). Most modems mentioned in this article are external units. These modems can be used on any microcomputer system, be it a PC, a Macintosh or an Amiga. Although only certain communication programs are used as examples, the discussions about setting up software apply to packages not covered herein.

It is assumed that the reader knows the basics about going online. For example, we would not discuss how to connect an external modem to your computer, nor would we explain what 8-N-1 means. This file is in the IBM ASCII format. Each line ends with a linefeed and a carriage return. If you use a Macintosh, open the file with a text editor and get rid of the linefeeds. (I recommend McSink, a shareware text editor widely available. Just launch McSink and open the file, then choose the Convert menu and select Strip Linefeeds.)

To print this document, use a 10-pitch (12 characters per inch) mono-spaced font, such as Courier.

Every effort has been made to supply current and accurate information. However, information contained herein is subject to change without notice and should not be construed as a commitment by the author who assumes no responsibilities for any errors that may appear.

Trademarks: The author has attempted throughout this document to distinguish proprietary trademarks from descriptive terms by following the capitalization style used by the manufacturer.


I. Introduction

II. Modulation Protocols

  1. 2400-bps modems
  2. High-speed modems
    a. V.32
    b. V.32bis
    c. US Robotics HST
    d. Telebit PEP & Turbo PEP
    e. Hayes Express 96
    f. CompuCom CSP
    g. Other proprietary protocols
  3. Things to come
    a. V.fast
    b. ISDN

III. Error Control Protocols

  1. V.42 and MNP4
  2. V.42 and MNP4 can provide error-free connections
  3. V.42 and MNP4 can improve throughput
  4. Are MNP 4 and V.42 useful?

IV. Data Compression Protocols

  1. MNP5 and V.42bis
  2. Are MNP5 and V.42bis useful?
  3. Compression by software vs. MNP5/V.42bis
  4. Local flow control and data buffering
  5. Macintosh and high-speed modems
  6. PC and UART
  7. Hayes ESP

V. About Fax Modems

  1. Protocols
    a. Group 3
    b. V.27ter
    c. V.29
    d. V.17
    e. CAS
    f. Class 1 & Class 2
  2. How useful is a fax modem?

VI. Profiles of High-speed modems

  1. ATI 9600etc/e
  2. CompuCom SpeedModems
  3. Hayes modems
  4. Intel modems
  5. Microcom modem
  6. Practical Peripherals modems
  7. Prometheus modems
  8. Supra modem
  9. Telebit modems
  10. US Robotics modems
  11. Zoom Modems
  12. Things to come

VII. Buying a High-speed Modem

  1. Should you pay extra for a V.32bis modem?
  2. Should you buy a modem with a proprietary modulation protocol?
  3. Should you buy a 2400-bps modem with V.42bis?
  4. Beware of the ads

VIII. Setting Up Software to Work with High-speed Modems

  1. The proper software setup
  2. Does your software initialize the modem properly?
  3. Does your software configure itself to match the modem settings?
  4. Why you may need to change the initialization string
  5. Editing the initialization string
  6. Match software settings to the modem settings
    a. Speed setting
    b. Hardware flow control
    c. Dialing time-out value

IX. Configuring Popular Communications Software to Work with High-speed Modems

  1. Procomm Plus 2.0
  2. Telix
  3. Qmodem
  4. HyperAccess 5
  5. Crosstalk for Windows
  6. MicroPhone II (for Macintosh)
  7. White Knight (for Macintosh)
  8. ZTerm (for Macintosh)

X. Other Settings for Your Communications Software

  1. Telephone number
  2. Dial string: ATDT
    a. PBX
    b. Call waiting
  3. 8-N-1 or 7-E-1 (data bits - parity - stop bits)
  4. Half vs. full duplex: local echo
  5. Terminal emulation
  6. Communications port
  7. File transfer protocols
    a. ASCII
    b. Xmodem
    c. Xmodem-1K
    d. Ymodem
    e. Ymodem-g
    f. Zmodem
    g. Kermit
    h. Which file transfer protocol should you use?

Appendix A: Resources
Appendix B: How to reach the author
Appendix C: What's "The Joy of Telecomputing"
Appendix D: What's in "Life beyond CompuServe"
Appendix E: What's in "Is AT&T the right choice?"
Appendix F: Updates, bulletins, and tutorial articles
Appendix G: How to order "The Joy of Telecomputing"