DATASTORM TECHNOLOGIES, INC. TECHNICAL BULLETIN #9 Rev. 1.0

Why Is There No 14.4k Baud Setting in PROCOMM PLUS?

SUMMARY
This document will explain the confusing and often misunderstood question of
why there isn't a setting for 14.4k baud in PROCOMM PLUS or PROCOMM PLUS for
Windows.

SYMPTOMS
"I just bought a new 14.4 modem, but PROCOMM PLUS skips from 9600 to 19200
bps. How can I use my 14.4k modem with your program?"

EXPLANATION
Is there something wrong with my modem or your software?

No, there is nothing wrong with either your modem or software. PROCOMM PLUS
2.01 and PROCOMM PLUS for Windows will support your new 14.4k modem with ease.

What do I set the baud rate to?

Your new 14.4 modem can actually operate at two baud rates, sometimes called
"split baud." The first baud rate is the carrier speed between your modem and
the host system's modem. This is known as the DCE (Data Communications
Equipment) speed. The second baud rate is the rate between your modem and
your computer. This is known as the DTE (Data Terminal Equipment) speed and
this speed is what PROCOMM PLUS 2.01 and PROCOMM PLUS for Windows use. Since
PROCOMM PLUS and PROCOMM PLUS for Windows use the DTE speed when you install
your modem, the program will set your baud rate to either 38,400 bits per
second (bps) or 57,600 bps.

Why do you set the baud rate so high?

Your modem is capable of receiving data at a very fast rate (e. g., 57,600
bps), buffer that data, compress it, then send that compressed data to another
modem, which then uncompresses it and sends it to the other computer at a
similarly high rate. One example, and one of the most common forms of data
compression, is called "v.42bis" which offers a 4:1 compression ratio. In
other words, if you send 4,000 bytes of data to your modem, your modem, with
v.42bis active, can conceivably compress that data down to 1,000 bytes. You
can take the 4:1 compression ratio and multiply it towards your modems carrier
speed of 14.4k bps:

4:1 v.42bis ratio Carrier Speed of Modem Throughput Speed
4 X 14,400 bps = 57,600 bps

You will notice that 57,600 bps is considerably higher than 14,400 bps. If
you set your DTE speed to 14,400 bps, you won't be able to send data to your
modem fast enough to allow it to compress it before sending, defeating the
purpose of your modem's high speed features.

RELATED TOPICS
Becker, Philip, et al. Introduction to PC Communications. Carmel: QUE, 1992

DATASTORM Technical Bulletin #1: "My Modem is Not Listed. What Do I Do?" for
a complete list of instructions on how to reconfigure both PROCOMM PLUS and
PROCOMM PLUS for Windows to work with your new modem.

DATASTORM Technical Bulletin #7: "High Speed Modem Setups," for a good
general discussion of high speed modems, error correction, data compression,
and split baud rate transmission techniques. See also SPLIT.TXT in Library 1
of the DATASTORM Forum on CompuServe and the DATASTORM BBS for a similar
discussion.

COMMENTS
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understand the technology you are using? If you still have questions, don't
hesitate to contact our Technical Support Department for further assistance.
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too. Please send comments to the Faxable Documents Administrator.

DATASTORM Technologies, Inc. Tech Support: 314.875.0530
P.O. Box 1471 Fax: 314.875.0595
Columbia, MO 65205 BBS: 314.875.0503