V. About Fax Modems

Since fax machines are essential business tools today, it has become a trend for modem vendors to add fax capability to their products.

A fax machine is made up of a scanner, printer and fax modem. The sending fax machine scans a sheet of paper and convert its image into a code for transmission over the telephone line. The receiving machine reconverts the codes and prints a facsimile of the original. (However, some fax modems can send and receive fax, while others can only send but not receive fax.)

V.1. Protocols

Here are some terms you'll need to know about fax modems:

V.1.a. Group 3

Group 3 is the international standard for communication between two fax devices (fax machines or fax boards). Fax machines have evolved over the past 20 years. Groups 1 and 2 fax machines transmit a single page at six and three minutes respectively and were used throughout the 1970s. Group 3 transmits one page in as little as 20 seconds (at 9600 bps). Group 3 resolution is 203x98 dpi in standard mode and 203x196 dpi in fine mode. Virtually all fax machines sold in the market today are Group 3 units.

V.1.b. V.27ter

V.27ter is the modulation scheme used in Group 3 Facsimile for image transfer at 2400 and 4800 bps.

V.1.c. V.29

V.29 is the modulation scheme used in Group 3 Facsimile for image transfer over dial-up lines at 9600 and 7200 bps.

V.1.d. V.17

V.17 is a new CCITT standard. It's the modulation technique for use in extended Group 3 Facsimile that allows 12000- and 14400-bps fax transmission.

V.1.e. CAS

CAS (Communications Application Specification) is a communications protocol developed by Intel and DCA (the software company know for Crosstalk) for a combination fax and modem board that allows personal computer users to exchange data more easily with fax machines. CAS was introduced in 1988. It has been supported in many applications software (e.g. WordPerfect).

V.1.f. Class 1 & Class 2

In the past, no standard existed for a microcomputer to deal with a fax board. As a result, the software for a particular fax board won't work with another fax board from a different manufacturer. (Although CAS has been moderately successfully, it hasn't become the industry standard.) The Electronic Industries Association/Telecommunications Industry Association (EIA/TIA) has been developing new standards (Class 1 & Class 2) for microcomputers to communicate with fax modems. As a result, you can buy a software program that will work with Class 1 (or Class 2) fax modems from different manufacturers.

The Class 1 standard provides minimal hardware support for sending a fax from a microcomputer, while Class 2 adds over 40 AT-command set instructions and places more functionality into the modem.

Note that the Class 2 standard is not expected to be finalized until August, 1992. In fact, most "Class 2" fax modems in the market today are based an obsolete draft. (It has become epidemic for computer vendors to announce products that are supposed to meet a standard while the standard doesn't even exist yet.)

V.2. How useful is a fax modem?

A fax modem may not be as useful as you'd think. (Personally, I don't find fax modems to be useful or reliable. But I know people who can't do without their fax modems.) Fax modems are good for sending, but not receiving fax. You may still need (or want) a fax machine even if you have a fax modem.

Fax machines are easy to use. Fax modems are not. Anyone that knows how to use a phone can learn to use a fax machine within a few minutes. A fax machine will work no matter what kind of computer you have. It also doesn't matter what operating system or environment you are running on your computer.

To use a fax modem, you may need to use a (sometimes more than one) software program. I use DOS, Windows, and OS/2 on my PC. The DOS software for the fax board is clumsy and hard to use, the Windows software is easy but unbearably slow. (A two-page resume took about 10 minutes to send with the fax board. I can print it out and send it with a fax machine in less than 3 minutes.) And the machine locked up many times while I tried do something else. (If you use Microsoft Windows, you should know that unrecoverable application errors are not gone. They are called general protection faults in Windows 3.1)

If you need to fax a printed document, you'll need to have a scanner to get it into your computer. To print out a fax received by your fax modem, you'd need a printer. Also, your computer needs to be on to receive fax.

However, there are several advantages for using a fax modem (if you can live with its shortcomings):

  1. You won't have a paper jam if you're faxing a multi-page document.
  2. The software for fax boards are more flexible and versatile. A fax board can be a life-saver if you regularly fax the same document to several people.
  3. You don't have to print out the document you want to fax if it's generated with your computer. And the quality is better.
It's worth noting that many documents that are faxed should be sent by e-mail. (A high-tech employment agency recently asked me to fax my resume and then had it re-typed into the computer. I suggested that I sent the resume by e-mail, but they didn't use e-mail.)

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