SGI Developer Toolbox 6.1/SGI Developer Toolbox 6.1 - Disc 4.iso/public/fax/src/doc/modems-faq

Text File | 1994-08-01 | 105KB | 2,401 lines

                      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.

=============================================================================

CONTENTS

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 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
        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"

=============================================================================

I.      Introduction

Buying and using a modem used to be relatively easy. Not so long ago, almost
all modems were 1200- or 2400-bps units and they were all compatible with the
Hayes Smartmodems (although some were more Hayes-compatible than others). How
time have changed.

Today, modems not only run faster, they are also loaded with features like
error control and data compression. Suddenly, you are confronted with all the
buzzwords: V.32, V.32bis, V.42, V.42bis, MNP5, LAP-M, etc. What do they mean?
And what do they mean to you?

To make the most of a high-speed modem, you need to understand three different
kinds of protocols and the relationships among them. They are the modulation
protocols, error control protocols and data compression protocols.


II.     Modulation Protocols

Modem stands for MOdulator/DEModulator. A modem converts digital signals
generated by the computer into analog signals which can be transmitted over a
telephone line and transforms incoming analog signals into their digital
equivalents.

The specific techniques used to encode the digital bits into analog signals
are called modulation protocols. The various modulation protocols define the
exact methods of encoding and the data transfer speed. In fact, you cannot
have a modem without modulation protocols. A modem typically supports more
than one modulation protocols.

The raw speed (the speed without data compression) of a modem is determined by
the modulation protocols. High-speed modems are modems that feature modulation
protocols at 9600 bps or higher. A 2400-bps modem with data compression that
can theoretically yield a 9600-bps throughput is not a high-speed modem.

"CCITT" is a French acronym for the International Telegraph and Telephone
Consultative Committee. CCITT, a United Nations agency, is an international
telecommunications standards committee that makes recommendations on a broad
range of subjects concerning data communications.

II.1.   2400-bps Modems

A 2400-bps Hayes-compatible modem typically supports the following modulation
protocols:

        Bell 103                (300 bps U.S. Standard)
        Bell 212A               (1200 bps U.S. Standard)
        CCITT V.22              (1200 bps standard outside the U.S.)
        CCITT V.22bis           (2400 bps International Standard)

Some 2400-bps modems also support the following protocols:

        CCITT V.21              (300 bps standard outside the U.S.)
        CCITT V.23              (1200/75 and 75/1200 bps, used in Europe)

In the past, most 2400-bps modems did not support any error correction or data
compression protocols. Recently, however, many modem manufacturers have
introduced 2400-bps modems with extra features like data compression, error
correction and fax capability.

II.2.   High-speed Modems

There are two standard modulation protocols for  high-speed modems: V.32 and
V.32bis. Both are standards established by the CCITT.

II.2.a. V.32

This is the standard for 9600 (and 4800) bps modems. CCITT V.32 is adopted by
the CCITT in 1984. But the market has not taken off until recently. V.32
modems used to cost more than modems using proprietary modulation protocols
(Hayes introduced the Smartmodem 9600, a V.32 modem, in 1988 with a $1999
price tag). But it is no longer true. At present, street prices for most V.32
modem are below $500. Every modem manufacturer is making V.32 modems now.
Packet-switching networks like Sprintnet (Telenet) and CompuServe are also
starting to support V.32 modems. Companies that make modems with proprietary
modulation protocols are making modems with "dual standard." U.S. Robotics,
Telebit, Hayes and CompuCom all have modems that support V.32 and their own
proprietary protocols.

II.2.b. V.32bis

V.32bis, established in early 1991, is the CCITT standard for 14400-bps
modems. A V.32bis modem also can fall back to 12000, 9600, 7200 and 4800 bps.
V.32bis is downwardly compatible with V.32.

Unlike 2400-bps modems where a single modulation protocol (V.22bis) is
supported by all modem makers, there are several proprietary modulation
protocols used by modems from different manufacturers. Two notable examples
are the U.S.Robotics HST and the Telebit PEP.

In the past three months, U.S. Robotics, Telebit and Motorola Codex have
introduced new modems using proprietary protocols that yield better throughput
than V.32bis modems.

II.2.c. U.S. Robotics HST

Until the recent surge of V.32 modems, the U.S. Robotics HST (High Speed
Technology) was the de facto standard in the PC-based BBS community. U.S.
Robotics introduced the Courier HST modem in 1986 and pioneered the market for
high-speed modems in the IBM PC environment. The immense popularity of the HST
modems was partly due to the generous discount program U.S. Robotics offered
to the BBS Sysops (SYStem OPerators). Many modem manufacturers have
implemented similar Sysop discount programs, but most BBS sysops remain loyal
to the U.S. Robotics modems.

The original Courier HST modem ran at 9600 bps. U.S. Robotics later (in 1989)
improved the speed of the Courier HST to 14400 bps. In March 1992, U.S.
Robotics further enhanced HST to 16800 bps (which yields an effective
throughput around 2000 cps with compressed files). Don't be surprised to see a
U.S. Robotics modem with a 19200-bps HST mode in the near future.

Although U.S. Robotics remains committed to the HST modems, there are now
three different high-speed Courier modems available: the Courier HST (which
only supports the HST protocol), the Courier V.32bis (which only supports
V.32bis) and the Courier HST Dual Standard (which supports both the HST and
the V.32bis protocols).

II.2.d. Telebit PEP and Turbo PEP

Telebit introduced the TrailBlazer in 1985 that employed a proprietary
modulation protocol called PEP (Packetized Ensemble Protocol). While the
Courier HST is popular among BBS, Telebit modems dominate the UNIX UUCP and
Usenet communities. (Usenet, UUCP and the Internet are discussed in Part II).

The TrailBlazer Plus owes its success partly to its builtin support for the
UUCP g-protocol, thus allowing efficient and  flawless UUCP session. PEP also
performs well even with noisy telephone lines. The actual throughput is around
14400 bps. The TrailBlazer Plus has an installed base of more than 120,000
units.

Telebit also introduced a cheaper (and slower) PEP modem, the T1000, in 1988.

Like U.S. Robotics, Telebit recently announced Turbo PEP which has an
effective data tranfer throughput of 2300 cps (with compressed files). The
Telebit WorldBlazer is a dual-mode modem which supports both V.32bis and Turbo
PEP.

II.2.e. Hayes Express 96

Hayes entered the high-speed modem arena in 1987 with the introduction of the
V-series Smartmodem 9600. The modem used a proprietary modulation protocol
called Express 96 (also known as Hayes "Ping Pong" protocol). The V-series
modems have not been as successful as the U.S. Robotics or the Telebit modems.

II.2.f. CompuCom CSP

While every modem manufacturer was jumping on the V.32 bandwagon, CompuCom
bucked the trend and came out with the SpeedModem Champ in early 1991. It's a
9600 bps modem with a proprietary modulation protocol called CSP (CompuCom
Speed Protocol). The SpeedModem Champ was the only modem with a proprietary
protocol that costs less than a generic V.32 modem. (The internal SpeedModem
Champ was priced at $169. An external version was $199.) Hundreds of PC-based
bulletin board systems have installed the SpeedModem Champ. The Champ also
works as a Hayes-compatible 2400-bps modem with MNP2-MNP4 error control and
MNP5 data compression. (Unfortunately, CompuCom went out of business
recently.)

II.2.g. Other proprietary modulation protocols

There are modems using other proprietary modulation protocols. For example,
Motorola Codex (a subsidiary of Motorola Inc.) just announced the 326XFast
Series of modems. Although you may see those modems referred to as "V.fast",
they use a proprietary protocol. (It could take another 18 months for CCITT to
finalize the V.fast standard.) Motorola Codex is promising a free ROM upgrade
when the V.fast standard is established.

Two modems can establish a connection only when they share a common modulation
protocol. To connect at high speed, two modems have to support the same high-
speed modulation protocol. Therefore, a modem with a proprietary modulation
protocol can only establish a high-speed connection with another modem from
the same manufacturer. A U.S. Robotics HST modem can only establish a high-
speed connection (at 9600 or 14400 bps) with another HST or an USR Dual
Standard modem. A Courier HST modem cannot establish a high-speed connection
with a Courier V.32bis modem. They can only connect at 2400 bps. (All high-
speed modems in the market support the CCITT V.22bis modulation protocol).

On the other hand, two V.32 modems can talk to each other at 9600 bps. They do
not have to be from the same manufacturer. Two V.32bis modems can talk to each
other at 14400 bps. A V.32 modem can talk to a V.32bis modem at 9600 bps.

II.3.   Things to come

A V.32bis modem may seem fast comparing to a standard 2400 bps modem. But
there are applications that will require even faster modems to be really
usable.

II.3.a. V.fast

CCITT is working on a new modem standard, dubbed V.fast. If all goes well, the
next modem standard can materialize before the end of 1993, 1994, 1994. A V.fast modem is
expected to reach a raw speed of 19,200-24,000 bps over standard dial-up
telephone lines. (By the way, V.fast will probably be known as "V.34" when
it's finalized.)

II.3.b. ISDN

In a couple of years we may not need modems at all. Integrated Services
Digital Network (ISDN) has been coming for years. When will ISDN really become
available for the rest of us? It depends on your local telephone company. It
is estimated that by the end of 1994 about half the telephone connections in
the U.S. will has access to it. With ISDN, you won't need a modem since no
modulation or demodulation will be necessary. You will need an ISDN adapter
instead.

An ISDN line carries three digital channels: two "B" channels that carry
various kinds of data at 64,000 bps and a "D" channel at 16,000 bps that can
carry control signals or serve as a third data channel.
A single ISDN channel can transfer uncompressed data bidirectionally at 64,000
bps. Combine that with a data compression scheme and you will be able to
transfer data at hundreds of kilobits per second.

Eventually, ISDN will provide widely available, low-cost digital
communications for voice and data communication. Until ISDN is firmly in
place, high-speed modems will be with us for a while.


III.    Error Control Protocols

Besides high-speed modulation protocols, all current models of high-speed
modems also support error control and data compression protocols.

III.1.  V.42 and MNP4

There are two standards for error control (error-correcting, error correction)
protocols: MNP 4 and V.42. The Microcom Networking Protocol, MNP, is developed
by Microcom. MNP2 to MNP4 are error correction protocols. MNP5 is a data
compression protocol. V.42 is established by CCITT. V.42 actually incorporates
two error control schemes. V.42 uses LAP-M (Link Access Procedure for Modems)
as the primary scheme and includes MNP4 as the alternate scheme. Therefore, a
V.42 modem will be able to establish an error-controlled connection with a
modem that only supports MNP 4.

A modem that uses a proprietary modulation protocol may also use a non-
standard error control protocol. For example, Hayes V-series Smartmodem 9600
supports an error control protocol called LAP-B. CompuCom's SpeedModem Champ
also uses a non-standard error control protocol.

III.2.  V.42 & MNP4 can provide errorfree connections

Modems without error control protocols, such as most 2400-bps Hayes-compatible
modems, cannot provide error-free  data communications. The noise and other
phone line anomalies are beyond the capabilities of any standard modem to
deliver error- free data.

V.42 (and MNP 2-4) copes with the phone line impairments by filtering out the
line noise and automatically retransmitting corrupted data. If you have used a
standard Hayes-compatible modem, you probably notice some garbled characters
(like "@8d_\nw`[ce") show up on your screen from time to time. When two modems
establish an error-controlled connection, they are said to have a reliable
link and are capable of filtering out those garbled characters caused by the
line noise. Notice that the line noise is still there, it just does not show
up on your screen or the screen on the remote system.

The filtering process used by V.42 (and MNP 2-4) is similar to the error
correction scheme used by file transfer protocols (such as Xmodem). The two
modems use a sophisticated algorithm to make sure that the data received match
with the data sent. If there is a discrepancy, the data is resent.

What is the difference between error control protocols (such as V.42) and file
transfer protocols (such as Xmodem)?

For one thing, file transfer protocols provide error detection and correction
only during file transfers. File transfer protocols do not provide any error
control when you are reading e-mail messages or chatting with other people
online. In other words, an error control protocol is "on" all the time during
your online session and file transfer protocols are "on" only some of the
times, namely when you are sending or receiving files.

Even though an error control protocol is "on" all the time, we still need file
transfer protocols when two modems establish a reliable link. A modem works
with bit streams, timing and tones. It does not understand what a file is.
When you download or upload a file, your communications software needs to take
care of the details related to the file: the filename, file size, etc. This is
handled by the file transfer protocol which does more than error-checking.

Some file transfer protocols, most notably Ymodem-g and Imodem, are developed
to handle file transfer without performing any error-checking. The idea of
using a protocol like Ymodem-g is to eliminate the redundancy - thus improve
the transfer speed. Ymodem-g and Imodem should only be used with modems that
provide built-in error control protocols. These file transfer protocols do not
provide any error-detection or recovery capability. If a problem occurs during
the file transfer, the transfer session will be aborted.

Protocols like Ymodem-g or Imodem depend on the modems to provide assurance
for the integrity of data being transferred. However, you should know that a
reliable link between two modems does not provide absolute guarantee for the
data integrity during file transfer. When you call a remote computer, there
are really three links involved in the process. Besides the link between the
two modems, there are still one link between your computer and your modem and
another link between the remote modem and the remote computer. When two modems
make a reliable connection using V.42 or MNP 4, only the data integrity
between the two modems is  ensured. It is still possible for errors to occur
at either end between the serial port and the modem (in the cable) or in the
computer itself. (Fortunately, such errors are rare.)

For extra protection, you may still want to use a file transfer protocol  such
as Zmodem which also performs error checking even if you have a reliable link
with the remote system. There is a common misconception that Ymodem-g is much
faster than other file transfer protocols. Although Ymodem-g is significantly
faster than Ymodem, it offers little over Zmodem. Zmodem has proven to be
extremely efficient. (See benchmark below)

        Filename        Ymodem          Ymodem-g        Zmodem
        --------------------------------------------------------
        the-wave.txt    1527 cps        3261 cps        3296 cps
        dayrpt.arc       761 cps        1042 cps        1025 cps
        dayrpt.wks      1244 cps        2314 cps        2337 cps
        sunset.arc       745 cps         987 cps         965 cps
        sunset.pic      1297 cps        2594 cps        2588 cps
        text109k.arc     814 cps        1089 cps        1064 cps
        text109k.txt    1351 cps        2812 cps        2885 cps

Note:   The seven test files used throughout this article are available on the
Hayes BBS (800-874-2937). It is an excellent source for information about
Hayes products. The BBS also provides a database for thousands of BBS in the
U.S. Best of all, it is free.

Unless noted otherwise, the results are obtained by using the following:

Computer: Mac SE with Mobius Two Page Display with 68030 accelerator
Modem: ATI 9600etc/e (the modem is set as V.32 with V.42bis enabled)
Operating System: System 7.0
Communication Software: ZTerm (Comm port set to 38400 bps)
File Transfer Protocol: Zmodem

All results are reported by ZTerm. (I use several communication programs on
both IBM PC and Mac. All of them show the average throughput while file
transfer is in progress, but ZTerm actually produces a report after the
transfer is completed).

III.3.  V.42 & MNP4 can improve throughput

The other benefit of V.42 (or MNP4) is that it can improve throughput. Before
sending the data to a remote system, a modem with V.42 (or MNP 4) assembles
the data into packets and during that process it is able to reduce the size of
the data by stripping out the start and stop bits.

A character typically takes up 1 start bit, 8 data bits and 1 stop bit for a
total of 10 bits. When two modems establish a reliable link using V.42 or MNP
4, the sending modem strips the start and stop bits (which subtracts 20% of
the data) and sends the data to the other end. The receiving modem then
reinserts the start and stop bits and pass the data to the remote computer.

Therefore, even without compressing the data you can expect to see as much as
1150 characters per second on a 9600 bps connection. (Although the modem
subtracts 20% of the data, the speed increase is less than 20% due to the
overhead incurred by the error control protocol.) Here are the test results
obtained by downlaoding the same file (1) without any error control protocol,
(2) with MNP4, and (3) with V.42. No data compression protocol is used.

        Filename        No EC           MNP4            V.42
        --------------------------------------------------------
        the-wave.txt    935 cps         1151 cps        1128 cps
        dayrpt.arc      863 cps         1023 cps        1002 cps
        dayrpt.wks      898 cps         1071 cps        1052 cps
        sunset.arc      838 cps          971 cps         953 cps
        sunset.pic      903 cps         1080 cps        1065 cps
        text109k.arc    908 cps         1085 cps        1064 cps
        text109k.txt    937 cps         1150 cps        1127 cps


III.4.  Are MNP4 and V.42 useful?

Absolutely. Anyone that has ever used a standard modem can appreciate the
benefit of an error-free connection. And the increase in data throughput,
though modest, is nothing to sneeze at.


IV.     Data Compression Protocols

Besides error control protocols, all current high-speed modems also support
data compression protocols. That means the sending modem will compress the
data on-the-fly and the receiving modem will decompress the data to its
original form.

IV.1.   MNP5 and V.42bis

There are two standards for data compression protocols, MNP5 and CCITT
V.42bis. Some modems also use proprietary data compression protocols.

A modem cannot support data compression without utilizing an error control
protocol, although it is possible to have a modem that only supports an error
control protocol but not any data compression protocol. A MNP5 modem requires
MNP 4 error control protocol and a V.42bis modem requires V.42 error control
protocol.

Also note that although V.42 include MNP4, V.42bis does not include MNP5.
However, virtually all high-speed modems that support CCITT V.42bis also
incorporate MNP5.

The maximum compression ratio that a MNP5 modem can achieve is 2:1. That is to
say, a 9600 bps MNP5 modem can transfer data up to 19200 bps. The maximum
compression ratio for a V.42bis modem is 4:1. That is why all those V.32 modem
manufacturers claim that their modems provide throughput up to 38400 bps.

There are some 2400-bps modems advertised as having MNP5 but are not real MNP5
modems. These modems do not have MNP5 implemented in the modems themselves,
but rather depend on the communications software (e.g. Bitcom Deluxe) to do
the tricks. Besides being slower than the real MNP5 modems, these modems will
not provide an error-free connection unless you use the accompanying software.
If you buy one of these modems and decide to use your own software (e.g.
Procomm Plus), you have to treat the modem as a plain vanilla 2400-bps modem.

IV.2.   Are MNP5 and V.42bis useful?

Don't be fooled by the claim. It is extremely rare, if ever, that you will be
able to transfer files at 38400 bps. In fact, V.42bis and MNP5 are not very
useful when you are downloading files from online services. Why?

How well the modem compression works depends on what kind of  files are being
transferred. In general, you will be able to achieve twice the speed for
transferring a standard text file (like the one you are reading right now).
Decreasing by 50% means that you can double the throughput on the line so that
a 9600 bps modem can effectively transmit 19200 bps.

However, V.42bis and MNP5 modem cannot compress a file which is already
compressed by software. In the case of MNP5, it will even try to compress a
precompressed file and actually expand it, thus slow down the file transfer!
Here are the test results obtained by downloading the three compressed files
using (1) MNP4 without data compression, (2) MNP5, (3) V.42 without data
compression, and (4) V.42bis.

        Filename        MNP4        MNP5        V.42            V.42bis
        ----------------------------------------------------------------
        dayrpt.arc      1023 cps    946 cps     1002 cps        1010 cps
        sunset.arc       971 cps    935 cps      953 cps         950 cps
        text109k.arc    1085 cps    988 cps     1064 cps        1053 cps

If you have ever downloaded files from a BBS or online service, you know that
almost all files are in a compressed format. Therefore, you should only expect
to see an actual throughput between 950 to 1100 cps even if your V.32/V.42bis
modem is supposed to offer throughput "up to" 38400 bps.

Most PC files are in the ZIP format. Macintosh files are typically in the .SIT
(Stuffit) or .CPT (Compact Pro) format. Amiga files are usually in the ZOO,
ARC or LZH format. Note that GIF files are also in a compressed format.

IV.3.   Compression Software vs. MNP5/V.42bis

There are several reasons why compression software programs (such as PKZIP or
Stuffit) are superior to MNP5 or V.42bis.

1. Compressed files save disk storage space.

2. Compression software programs are more versatile. Most of them allow you to
group several files in a compressed file archive to ensure that all the
related files get transferred at the same time.

3. Software compression is more efficient than on-the-fly modem compression.
In the case of a small file, this may not make much difference. But the
difference can be significant when you are transferring large files.

        Filename        Size            Time            Throughput
        ----------------------------------------------------------
        the-wave.txt    143579 bytes    43 seconds      3296 cps
        dayrpt.arc        8423 bytes     8 seconds      1010 cps
        dayrpt.wks       19712 bytes     8 seconds      2337 cps
        sunset.arc        5084 bytes     5 seconds       950 cps
        sunset.pic       16391 bytes     6 seconds      2643 cps
        text109k.arc    29775 bytes     28 seconds      1053 cps
        text109k.txt    111386 bytes    39 seconds      2822 cps

As we can see from the test results, it is about 30% faster to transfer the
compressed file text109k.arc than to download the text file with V.42bis.

Hayes BBS does not provide a compressed version for the file the-wave.txt.
Using PKZIP (for PC) and Stuffit (for Macintosh), we obtain the following
results:

        the-wave.zip:           6812 bytes (PKZIP)
        the-wave.sit:           6081 bytes (Stuffit)

Assuming a transfer speed of 1000 cps, the compressed file can be downloaded
in 7 seconds. That's six times faster than downloading the text file with
V.42bis!

Here is another example. One of my  local BBS has a Macintosh TIFF file
(206,432 bytes) which can be downloaded in 56 seconds (with an effective
throughput of 3745cps) with a V.32/V.42bis modem.

The result may seem impressive at first. However, the file can be compressed
to 6065 bytes (with Compact Pro) or 7385 bytes (with Stuffit). Assuming a
transfer speed of 1000 cps, it would only take 68 seconds to transfer. Again,
it is seven to nine times faster than downloading the file with V.42bis.

On-the-fly modem compression does have one advantage. It is more convenient.
You can send a file without compressing it first and the recipient does not
need to decompress the file.

IV.4.   Local Flow Control and Data Buffering

To get the most from a modem with data compression, you'll want to send data
from your PC to the modem as quickly as possible. If the modem is idle and
waiting for the computer to send data, you are not getting the maximum
performance from the modem.

For example, you have a V.32/V.42bis modem and you want to send a text file to
a remote system which also has a V.32/V.42bis modem. Let's assume the modem is
able to send the file at 20000 bps using V.42bis. If your computer is sending
data to your modem at 9600 bps, your modem will have to stop and wait to
receive data from your computer.

To get the maximum performance, you want to set the computer to send data to
the modem at 38400 bps (the maximum a V.32/V.42bis modem can achieve). Since
the modem can only send the file to the other modem at 20000 bps, it will
never have to wait.

Here are the test results for downloading the text file thewave.txt by setting
the communication port at different speeds (usually referred to as "DTE
speed"):

the-wave.txt:    946 cps        (modem port speed 9600 bps)
                1885 cps        (modem port speed 19200 bps)
                3296 cps        (modem port speed 38400 bps)

However, there is a new problem. Since your computer is sending data faster
than the modem can handle, there needs to be some ways for the modem to ask
the computer to stop sending data. Otherwise, data loss is sure to occur. This
is where local flow control comes into play.

A high-speed modem typically supports two kinds of local flow  control:
hardware handshaking (CTS/RTS) and software handshaking (XON/XOFF). Of the
two, hardware flow control is the preferred method.
We have mentioned earlier that there are three links involved when you are
connected to a remote system:

1. The link between your computer and your modem
2. The link between the modems
3. The link between the remote modem and the remote computer

Local flow control is used for the first and third links. Notice that the
first link may not use the same kind of flow control as the third link.

Hardware flow control (or hardware handshaking) works by altering voltage
levels on the RTS (Request To Send) and CTS (Clear To Send) signal lines at
the RS232 serial interface between the modem and the computer.

CTS is used by the modem on the sending end of a transmission. When the local
modem is ready to receive data, it sends the CTS signal to the local computer
and the computer starts transferring data. If the modem is unable to accept
the data as fast as it is received from the computer, the modem will disable
the CTS to inform the computer that the modem buffer is almost full (A high-
speed modem typically contains a small amount of RAM which is used to provide
data buffers). The computer will then suspend data transfer. Once the local
modem has emptied its buffer by transmitting data to the remote modem, it will
enable CTS again.

RTS is used by the computer on the receiving end of a transmission. When the
computer cannot accept data at the rate at which the modem is passing data, it
will disable RTS. The computer enables RTS again when it is ready to resume
receiving data from the modem.

Software flow control (or software handshaking) is achieved by embedding
control character in the data stream. XON and XOFF are the most commonly used
control characters. XON is also known as ControlQ or DC3 (ASCII 19) while XOFF
is known as ControlS or DC1 (ASCII 17).

The use of XON and XOFF during data transfer can create problems when a binary
file contain the ControlS (^S) character as a legitimate part of the data. Do
not use this method if ^S and ^Q are part of the transmitted data.

IV.5.   Macintosh & High-speed Modems

If you use a Macintosh with a high-speed modem, you will need a special modem
cable that is wired correctly to support hardware handshaking. You can order
the cable from most mailorder companies that sell high-speed modems. I got
mine from Maya Computer (800-541-2318) for $10 (plus $2.50 for shipping &
handling).

Unfortunately, the cable did not work with my SE. The cable is good since it
worked fine on a Mac IIsi. It just refused to work on my SE. I was
disappointed but not surprised. After all, my SE is equipped with a 25 Mhz
68030 accelerator. (Well, it is actually both an accelerator and a video
adapter for a 19 inch dualpage monitor.) Since I will never want to run my SE
without the accelerator, I have no choice but to use software handshaking.

IV.6.   PC & UART

Your PC's serial port has a UART (Universal Asynchronous Receiver/Transmitter)
chip to control the input/output. The XT usually has an 8250 UART, the AT
usually has a 16450 UART. If you are running Windows, Desqview, OS/2 or any
other multitasking environment, you should upgrade your UART with the 16550
(if your PC does not already have one). The 16550 is standard in most IBM PS/2
and many 386based computers. The 16550 UART has a 16 bytes FIFO (first in,
first out) buffer that helps to prevent degradation when several programs are
running at the same time.

If you use an external modem, the UART is in your computer (either on the
motherboard or on an I/O card that has the serial port). If you use an
internal modem, the UART is on the modem. (Both internal modems from Practical
Peripherals and Zoom use the 16550 UART. The Twincom 96/42 uses a 16450. The
CompuCom SpeedModem Champ, due to its unique design, does not use a standard
UART.)

Even if you have a 16550 UART, the communication software that you use will
need to support it. Fortunately, the most recent versions of popular
communications programs are all designed to support the 16550 UART.

IV.7.   Hayes ESP (Enhanced Serial Port)

 Hayes makes an adapter called Enhanced Serial Port (ESP) that has two serial
ports complete with an onboard coprocessor. The ESP can save your PC's CPU
from having to manage the work load. If a 16550 UART is not good enough for
you, the ESP may be the only answer.


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.)

VI.     Profiles of High-speed Modems

Here are profiles of some high-speed modems. The list is not comprehensive,
nor is it intended to be. Unless noted otherwise, the street price quoted are
from PC Connection (800-243-8088) in PC Magazine (5/26/92). PC Connection
generally does not offer the lowest price, but the service is excellent. I
have dealt with PC Connection and MacConnection (800-800-4444) for years and
have yet to be disappointed with their services.

Unless noted otherwise, a V.32/V.42bis modem supports V.32, MNP2-5,
V.42/V.42bis. And a V.32bis/V.42bis modem supports V.32bis, MNP 2-5,
V.42/V.42bis. Some units also support MNP 10 which is developed to overcome
the hostile environment (such as celullar phone lines).

Some of the units mentioned here are fax modems.

VI.1.   ATI 9600etc/e

ATI Technologies is well known for their video adapters. But they also make a
V.32/V.42bis external modem. It is a generic high-speed modem that works well.
PC Connection is selling the ATI 9600etc/e at $369.

I have been using an ATI 9600etc/e for more than a year now and I am very
pleased with it. I will not hesitate to recommend it to anyone.

There are two things I really like about the ATI modem:

* It has a slide volume control on the outside so you can easily  adjust the
volume by hand.

* It has factory settings for three different modes: V.32 only, V.32 with
MNP5, V.32 with V.42bis. It is very convenient if you need to initialize the
modem in different ways.

VI.2.   CompuCom SpeedModems

As we mentioned earlier, CompuCom SpeedModem Champ offered a lowcost
alternative to PC users. CompuCom also made modems that implemented the V.32
and V.32bis protocols in addition to its proprietary protocol. Since CompuCom
is no longer in business, it's probably not a good idea to purchase a CompuCom
modem now.

VI.2.a. Champ

The SpeedModem Champ is a 9600 bps high-speed modem with CompuCom's
proprietary CSP modulation protocol. It is introduced in early 1991. The
CompuCom Champ is supported by hundreds of BBS in the U.S., including
heavyweights such as EXEC-PC and Channel 1.

VI.2.b. Storm

The SpeedModem Storm is a dual-mode modem. It supports both CSP and
V.32/V.42bis.

VI.2.c. Star
The SpeedModem Star is also a dualmode modem. It supports both CSP and
V.32bis/V.42bis.

VI.3.   Hayes Modems

Hayes used to be the leader in the modem market. The Hayes SmartModem 1200 and
2400 have been the industry standards for many years. However, Hayes has not
been as successful in the high-speed modem market.

VI.3.a. V-series Smartmodem 9600

Introduced in 1987, this is a high-speed modem that supports the proprietary
Hayes Express 96 modulation protocol. The V-series Smartmodem 9600 is still
available from various mail order vendors. There is also an internal unit
called V-series Smartmodem 9600B.

VI.3.b. Smartmodem 9600

Introduced in 1988, the Smartmodem 9600 is a V.32 modem. It does not support
any error control or data compression protocol. Don't confuse this unit with
the V-series Smartmodem 9600.

VI.3.c. Ultra 96

Ultra 96 is a dual-mode modem from Hayes. Introduced in 1990, the Ultra 96
supports both V.32/V.42bis and the Hayes Express 96 modulation protocol. Ultra
96 has many unique features that are not needed if you are calling BBS or
online services. The current street price is $669.

VI.3.d. Ultra 144

Ultra 144 is a dual-mode modem that supports both V.32bis/V.42bis and the
Hayes Express 96 protocol. The current street price is $799.

VI.3.e. Optima 96

Optima 96 is a plain vanilla V.32/V.42bis modem. This is Hayes' answer to the
"generic" V.32/V.42bis modem. The current street price is $389.

VI.3.f. Optima 144

Optima 144 is a plain vanilla V.32bis/V.42bis modem. This is Hayes' answer to
the "generic" V.32bis/V.42bis modem.

VI.4.   Intel Modems

Besides the 80x86 CPU, Intel also makes many peripherals for the IBM PC. The
Intel modems are solid products that perform well. The new SatisFAXtion 400
and 400e are priced aggressively to compete with the low-cost units offered by
other vendors.

VI.4.a. 9600EX

The 9600EX is a V.32/V.42bis modem.

VI.4.b. 14.4EX

The 14.4EX is a V.32bis/V.42bis modem. PC Connection is selling the 9600EX for
$469 and the 14.4EX for $549.

VI.4.C. SatisFAXtion 400 and 400e

Intel's original SatisFAXtion is arguably the best fax modem in the PC market.
Intel recently introduced two V.32bis/V.42bis fax modems - the SatisFAXtion
400 and 400e. The SatisFAXtion 400 is an internal unit for IBM microcomputers.
It carries a list price of $499. The SatisFAXtion 400e is an external unit
(with a list price of $549).

Both the SatisFAXtion 400 and 400e support Group3/Class 2/CAS fax at 14400
bps.

VI.5.   Microcom modem

Microcom is a major modem manufacturer. However, Microcom products are not
normally sold through retail stores or mail order companies.

MicroPorte 4232bis

As the name suggests, the MicroPorte 4232bis is a V.32bis/V.42bis modem. It
also supports MNP 10. The MicroPorte 4232bis is a pocket modem (the unit
measured 4.5x2.75x1.5 inches). The MicroPorte 4232bis lists for $899.

VI.6.   Practical Peripherals Modems

Practical Peripherals has been making Hayes-compatible modems for many years
(it's owned by Hayes, by the way). The Practical Peripherals modems are
compatible with the Hayes Ultra modems. Since the Hayes Ultra modems are
supported by most communications software, you wouldn't need to worry about
configuring the software to work with the Practical Peripherals modems.

VI.6.a. PM9600SA and PM9600

The PM9600SA is a V.32/V.42bis modem. It is designed to be compatible with the
Hayes Ultra 96. That means you can tell your communications software that you
have a Hayes Ultra 96. However, the PM9600SA only responds to a subset of the
commands supported by the Hayes Ultra 96. Any commands specific to the Hayes
Ultra 96 that are not implemented in the PM9600SA will be ignored.

Some early PM9600SA units have quite a few problems connecting to other V.32
modems. (Make sure you send in the warranty card.) Practical Peripheral has
since sent out several ROM upgrades and the current shipping units seem to be
working fine.

Practical Peripherals also makes an internal modem that features a 16550 UART.
You can get the PM9600SA for $289 and the internal PM9600 for $275. Both
PM9600SA and PM9600 now come with a lifetime guarantee.

VI.6.b. PM14400FXSA and PM14400FX

The PM14400FXSA ($399) is an external V.32bis/V.42bis modem. PM14400FX ($359)
is an internal unit. (Both of them come with a lifetime guarantee.) The modems
come with QuickLink II. I'm currently testing a PM14400FX. It seems to work
O.K. (However, the speaker died after a week of usage.)

The PM14400FXSA and PM14400FX support Group 3/Class 1 fax at 9600 bps.

VI.7.   Prometheus Modems

Prometheus modems are available from many Macintosh mail order companies.
Until recently, Prometheus is the only manufacturer that makes high-speed
modems with fax capability.

VI.7.a. Promodem 9600 Plus

Promodem 9600 Plus is a V.32/V.42bis modem. It can also send and receive Group
III fax at 9600 bps.

VI.7.b. Promodem Ultima and Ultima Home Office

Prometheus Ultima is a V.32bis/V.42bis fax modem. It can also send and receive
Group III fax at 9600 bps. The Ultima Home Office adds voice capability. PC
Connection sells the Ultima Home Office (internal) for $489. MacConnection
sells the Ultima Home Office (external) for $489.

VI.8.   Supra Modem

Although Supra is not be a household name, it's a major vendor in the market
for Commodore Amiga.

SupraFaxModem V.32bis

Supra announced the SupraFaxModem V.32bis at the Fall Comdex last year. With a
suggested list price of $399 (without software), the SupraFaxModem became one
of the most anticipated product in the past 6 months. However, Supra did not
ship the product on schedule. The SupraFaxModem was supposed to ship in
January but was delayed until March. There were also some problems with the
early units. If you're buying the SupraFaxModem, I'd recommend you purchase it
from a vendor that offers a money-back guarantee. (This recommendation applies
to all the inexpensive V.32bis modems.)

The SupraFaxModem V.32bis supports Group 3/Class2 fax.

VI.9.   Telebit Modems

Telebit makes several modems. The prices quoted for the Telebit modems are
their new list prices.

VI.9.a. TrailBlazer Plus

$849. Introduced in 1985, the Trailblazer has been the de facto standard in
the UNIX UUCP and Usenet communities. With the new pricing, you should
consider the T2500 or the T3000 instead of the TrailBlazer Plus if you need to
connect to a Telebit PEP modem.

VI.9.b. T1000

Introduced in 1988, the T1000 is the little brother of the TrailBlazer Plus.
The T1000 supports PEP at a slower speed. The actual throughput is about 9600
cps. The current list price is $699. Unlike the TrailBlazer Plus, the T1000
does not have callback or password security.

VI.9.c. T2500

$949. Introduced in 1989 when V.32 modems started to enter the market, the
T2500 supports both V.32/V.42bis and PEP. The maximum throughput is 19,200 bps
due to the limitation imposed by the older Rockwell chipset used.

VI.9.d. T1600

$699. The T1600 is a V.32/V.42bis modem introduced  in 1991. It provides
builtin support for UUCP and offers password and callback security.

VI.9.e. T3000

$949. This is a V.32bis/V.42bis modem. If you need PEP, you can upgrade the
T3000 to a WorldBlazer (see below).

VI.9.f. QBlazer

$599. QBlazer is the first portable V.32/V.42bis modem (2.3"x2.4"x2.4"). It
works with a 9-volt battery for about two hours.

VI.9.g. WorldBlazer

This is the latest and greatest Telebit modem. The WorldBlazer is a dual-mode
modem that is equipped with Turbo PEP and V.32bis/V.42bis. If you already own
a Telebit modem, you can purchase a WorldBlazer (for $549) through Telebit's
Loyalty Pays Again program until June 30, 1992.

Note that T1600, T2500, T3000, and the WorldBlazer all offer the following
features:

* Built-in support for UNIX UUCP, Xmodem, Ymodem, Kermit file transfer
protocols
* Two types of dial-access security: password security and call-back security
* Remote management and diagnostics

VI.10.  U.S. Robotics Modems

U.S. Robotics has been extremely successful with its high-speed modems. Here
are its current offerings:

VI.10.a.        Courier HST

This is the modem that made U.S. Robotics the king of PC-based BBS
communities. Unless you are only going to communicate with other USR HST
modems, it is probably not a good idea to purchase this unit. The street price
for a Courier HST is $550-$600.

VI.10.b.        Courier V.32bis

Introduced in 1990, this is a V.32bis/V.42bis modem. It does not support HST.
The current street price for a Courier V.32bis is $530-$570.

VI.10.c.        Courier HST Dual Standard

This unit is introduced in 1990. If you need to connect to HST modems and also
want to be able to talk to other V.32/V.32bis modems, this is the modem to
buy. Its current street price is around $800. The street price for a HST Dual
Standard is $800. (Note that earlier HST Dual Standard modems only support
V.32 and not V.32bis.) The HST Dual Standard is considered by many BBS users
as the best modem money can buy. In March 1992, U.S. Robotics shipped a
Courier Dual Standard with a 16800-bps HST mode.

The only reservation I have about the Courier modems is their size. The
external Courier modems are rather bulky: 8.3" wide, 12.65" deep, 1.57" tall.
I would not want to carry one of these with me when I travel. Incidentally,
the new Courier Dual Standard is substantially trimmer in size.

VI.10.d.        Sportster 9600 V.42bis

This unit is introduced in 1991. The Sportster  9600 is an entry level
V.32/V.42bis modem from U.S. Robotics. The list price is $645 for the external
version. ($595 for the Internal version).

VI.10.e.        WorldPort 9600 V.32

The WorldPort 9600 is a portable pocket modem. Originally made by Touchbase
Systems, the WorldPort 9600 is a V.32/MNP5 modem. It does not support
V.42/V.42bis. The WorldPort 9600 works with a 9-volt battery. The list price
is $699.

V.11.   Zoom Modems

Zoom Telephonics has been making Hayes-compatible modems for quite some times
now. I have used many Zoom modems in the past and they have proven to be
reliable and inexpensive.

VI.11.a.        V.32 Turbo

Zoom has been making Hayes-compatible modems for a long time. The V.32 Turbo
is their entry into the high-speed modem arena. The V.32 Turbo is a
V.32/V.42bis with a 12000 bps turbo mode which is compatible with a V.32bis
modem at 12000 bps. Zoom also makes an internal version of the V.32 Turbo that
features a 16550 UART. PC Connection sells the the internal model for $329.

VI.11.b.        VFX V.32bis and VFP V.32bis

VFX V.32bis is an external V.32bis/V.42bis modem (list price $449). The
internal version is called VFP V.32bis ($399). Both come with MTEZ (which
includes ExpressFax) for IBM PC. Zoom also offers a Macintosh version that
comes with QuickLink II ($449). MacConnection is selling the VFX V.32bis for
$299.

The Zoom VFX V.32bis and VFP V.32bis support Group3/Class 2 fax.

VI.12.  Things to come

Almost every modem manufacturer makes at least one V.32/V.42bis modem and a
V.32bis/V.42bis modem now. The price for V.32 and V.32bis modems will continue
to drop. In the past few months, the price difference between V.32/V.42bis and
V.32bis/V.42bis modems is diminishing.

Many new modems introduced in the past few months also offer fax capability.
You can expect modem manufacturers to include fax capability as a standard
feature in their products if they haven't done so already.

VII.    Buying a High-speed Modem

V.32 and V.32bis modems are clearly the standards of high-speed modems today.
You should buy a V.32 or a V.32bis modem unless

1. Your application requires a high-speed modem with a proprietary modulation
protocol. In this case, you should consider a dual-mode modem that support
both the proprietary protocol and V.32 (or V.32bis).

2. You cannot afford a V.32 modem.

VII.1.  Should you pay extra for a V.32bis modem?

A V.32bis modem costs substantially more than a V.32 modem just a few months
ago. However, the price difference bewteen a V.32bis and a V.32 modem (from
the same manufacturer) are diminishing. If you're thinking about buying a
high-speed modem, you should probably look for a V.32bis modem.

Assuming the remote system support V.32bis, a V.32bis modem will  pay for
itself rather quickly if you are placing long distance calls to the remote
system. However, if you are using some packet-switching networks to reach the
remote system by calling a local number. A V.32bis modem will be wasted since
none of the packet-switching networks currently support V.32bis. In fact, they
are just starting to offer 9600 bps access service. Part III of "The Joy of
Telecomputing" provides a comprehensive discussion of the issues involved.

VII.2.  Should you buy a modem with a proprietary protocol?

It is generally not a good idea to purchase a modem which only supports a
proprietary modulation protocol. You should consider getting a modem that
supports dual modulation protocols (USR Courier Dual Standard, Telebit
WorldBlazer, Hayes Ultra) if (i) you have to connect to a modem that uses a
proprietary modulation protocol, or (ii) you need to have better throughput
than a V.32bis modem can offer.

VII.3.  Should you buy a 2400-bps modem with V.42bis?

If you are thinking of purchasing a 2400 bps modem with V.42bis data
compression, think again.

We have mentioned earlier that V.42bis and MNP5 are useless for downloading
compressed files. There is one more reason why a 2400 bps with V.42bis is
generally not useful when you are calling commercial online services or BBS.

Online services and BBS usually have separate phone numbers for 2400-bps and
high-speed modems. Most of them do not support V.42bis on their 2400-bps
lines. Therefore, you won't be able to make a connection with V.42bis if you
call their 2400-bps modem lines.

Couldn't you call their 9600 bps lines? Well, not really. Commercial online
services, as well as many bulletin board systems, typically do not allow you
to call their high-speed modem lines with a 2400-bps modem. You won't be able
to make a connection even if you try.

VII.4.  Beware of the Ads

Current V.32 modems typically support MNP 2-5 and V.42/V.42bis. However, there
are still some earlier models of V.32 modems in the market which

1. may not support any error control or data compression protocol (Hayes
Smartmodem 9600).
2. may support MNP 2-5 but not V.42/V.42bis.
3. may support proprietary data compression protocol (Microcom MNP9).
4. may support V.42 but not V.42bis (Prometheus).

When a modem is said to offer a 38400 bps speed (or throughput), it may mean
that

1. it is a V.32 or V.32bis modem with V.42bis
2. it is a V.32 modem with proprietary data compression protocol (some
Microcom modems)
3. it is a high-speed modem with proprietary modulation protocol and V.42bis
(U.S. Robotics Courier HST)
4. it is a high-speed modem with proprietary modulation protocol and
proprietary data compression protocol (CompuCom Champ)

An ad that says "USR modem, 38400 bps throughput, V.42bis" does not tell us
anything except that the modem is made by U.S. Robotics. It could be any one
of the three Courier modems. It could even be a Sportster 9600.

When a modem is said to offer a 9600 bps speed (or throughput), it may mean
several things:

1. it is a V.32 modem
2. it is a high-speed modem using proprietary modulation protocol (Hayes
   V-series Smartmodem 9600, Telebit 1000, etc).
3. it is a 2400 bps modem with V.42bis data compression.
4. it is a 2400 bps modem with 9600 bps fax
5. it is a 2400 bps modem both V.42bis and fax.


VIII.   Setting Up Software To Work With High-speed Modems

Getting a high-speed modem is only half the battle. You will need to get it to
work with your communications program. Most communications programs still come
with settings configured for standard 2400-bps modems.

Since all 2400- bps modems are Hayes-compatible, it is relatively easy to set
up the software. You simply install the software as if you had a Hayes modem.
The software usually will work flawlessly. And you don't really have to worry
about things like the initialization string.

Getting a high-speed modem to work with your software is a different story.
There is no longer a Hayes standard that everyone follows. Here are some of
the reasons why you need to know how to configure your high-speed modem to
work with your communications program.

First, your high-speed modem may not be supported by your software.

Secondly, even if your software supports your high-speed modem, the software
may not be set up properly.

Finally, even if your software is set up properly, the settings may not work
all the times.

VIII.1. The Proper Software Setup

When we say that the software is set up properly, we mean that

1. the modem is initialized properly by the communications software, and
2. the settings of your software match those of the modem

What is the proper way to initialize a high-speed modem? In general, your
modem needs to be initialized to:

1. Enable V.42bis Data Compression
2. Enable hardware flow control
3. Handle the DTR and CD signals properly (by adding &C1&D2 to the modem
   initialization string)

We'll use the ATI 9600etc/e modem as an example for our discussions below. The
initialization string described here is for the ATI modem only. Refer to your
modem manual for the equivalent initialization string for your modem.

The ATI modem is supported by two popular communications programs: Qmodem and
HyperAccess 5. Qmodem initializes the modem and also configures itself to use
hardware flow control. HyperAccess 5 also initializes the modem properly,
however it does not configure itself to use hardware flow control.

All modems come with default settings preconfigured from the factory. Many
V.32 high-speed modems are preset to use V.42bis and hardware flow control
when they are turned on. This optimal configuration enables the modem to
automatically negotiate a connection with either another V.32 modem supporting
V.42bis or  MNP protocols (or even a standard modem).

Interestingly enough, not all high-speed modems are configured this way. The
ATI 9600 etc/e modem, for example, is preset to use V.32 without error control
or data compression at poweron. (Why? Good question.)

As a result, your communications program needs to issue the appropriate
initialization string (AT&F2) to set up the ATI modem to use V.32 with V.42bis
and hardware flow control.

There is another change required. And it has to do with the parameters
controlling how the modem deals with two of the RS232 signals: DTR (Data
Terminal Ready) and CD (Carrier Detect).

CD is a signal generated by the modem which is used to indicate its connection
status. DTR is a signal generated by your computer. DTR is used to enable the
modem to accept commands from your communications program, it is also used by
most modems to determine when to disconnect a call.

The factory default setting for DTR tells the modem to ignore change in DTR
(&D0), and the setting for CD forces CD always on (&C0). These specific
settings are required by some dedicated dumb terminals in order to communicate
with the modem. (Virtually all modems use &C0&D0 as the default setting.)
However, these settings will often cause problems when hanging up the phone
lines or produce an error message which says the modem is online when it is
not.

Most communications software programs expect the modem to follow DTR and
expects CD to follow carrier. "&C1&D2" sets the parameters for the modem to
handle the DTR and CD signals as expected by most communications programs.
(However, if you use a Mac, you should use "&C1&D0".)

Therefore, the proper initialization string to use for the ATI modem should be
"AT&F2&C1&D2" if you have a PC, and "AT&F2&C1&D0" if you have a Macintosh.

VIII.2. Does Your Software Initialize the Modem Properly?

Let's take a look at the initialization strings used by Qmodem and HyperAccess
5 for the ATI 9600etc/e modem.

HyperAccess 5 use the following initialization string

        AT&F2E1V1L0Q0W2X4&C1&D2S11=55

This string is longer than the one we suggest. But does it do more? Actually
it doesn't. Many of the commands in the string are redundant or not necessary.
Only AT&F2&C1&D2 are crucial.

Four of the commands E1, V1, Q0 and X4  are redundant since they are
duplications of the factory default settings. (Check your modem manual to find
out what they mean. Since you would most likely need to read it sooner or
later, you might as well get started now.)

L0 does not apply to the ATI modem. L0 normally is used to set modem speaker
volume to the lowest level. However, the ATI 9600etc/e modem does not respond
to the L0 command. Unlike most modems, the ATI modem has a slide volume
control on the right side for adjusting the volume level.

The other two commands (W2 and S11=55) are not redundant, but they are not
necessary.

W2 sets the modem to report Negotiation result codes in single line format
instead of the default three line format (W1).

        Three line format:              Single line format:
        -------------------------------------------------
        CARRIER 9600                    CONNECT 9600/LAP-M
        PROTOCOL: LAP-M
        CONNECT 38400


S11=55 (default is 95) sets the modem to dial at a faster speed than the
factory setting.

Despite the fact that its initialization string contains some redundant
commands, HyperAccess 5 does properly initialize the ATI modem.

Although HyperAccess 5 will initialize the modem with the string every time
you dial a remote system, the program does not change the factory default
settings for the ATI modem (which is V.32 without error control or data
compression). Every time you turn the modem off and back on, the modem will
revert to its factory defaults.

Unlike HyperAccess 5 (and other communications programs), Qmodem does it in a
different way. It actually replaces the old factory default setting (AT&F) of
the ATI modem with a new default configuration (AT&F2&C1&D2).

When you first install Qmodem to work with an ATI 9600 etc/e modem, the
program sends the following two strings to the modem (make sure the modem is
connected to your PC and is turned on):

        AT&F2^M AT&C1&D2&W^M

The first string sets the modem as V.32 with V.42bis enabled, hardware flow
control enabled (among other things). Note that ^M is equivalent to sending a
Carriage Return to the modem.

The second string changes the factory settings of the CD and DTR (&C0&D0) and
then write (&W) all the new active configuration settings to the nonvolatile
memory of the modem. The new settings are now stored by the modem and become
the new default configuration when the modem is powered on (or when it
received the ATZ command).

Thus, Qmodem simply sends the initialization string "ATZ^M" (which resets the
modem to its default state, now AT&F2&C1&D2) to the modem whenever you load
the program.

Although the two programs use different techniques, the result is the same.
The modem is initialized as V.32/V.42bis with hardware flow control enabled,
which is normally the optimum setting.

VIII.3. Does Your Software Configure Itself to Match the Modem Settings?

Besides sending the right initialization string to the modem, the
communications software will also need to match the modem setting.
Specifically, the communications software should also use hardware flow
control since the modem is initialized with hardware flow control enabled.

One would expect that when a software initializes the modem to use hardware
flow control, the software itself would also use hardware flow control. But it
is not always true. As we mentioned earlier, HyperAccess 5 initializes the
modem with hardware flow control enabled, but expect you to change the flow
control settings in each individual dialing entry.

VIII.4. Why You May Need to Change the Initialization String

In general, the string AT&F2&C1&D2 should work without any problem. But there
is no guarantee that it will  always work. When it does not work, you'll
normally need to change the initialization string to solve the problems.

Here are a few reasons why the initialization string used by your
communications program may not work:

1. The settings need adjustments to work with the system you are calling.

Case 1: When I called the Hayes BBS, the modem would abort and failed to make
a connection. It turned out that the default setting (30 seconds) of the S7
register is not long enough for the ATI modem to make a connection with the
Hayes Ultra modem on the other end.

Solution: To establish a connection to the Hayes BBS, I need to add "S7=60" to
the modem initialization string and also change the setting in the
communications software to wait 60 seconds for a connection.

By initializing the modem with the string AT&F2&C1&D2S7=60, I was able to
connect without any problem. (The default setting for the S7 register is not
universal, the Hayes Ultra and Practical Peripheral use 50 seconds as the
default value.) Note that there is nothing special about the number 60. In my
particular case, any number larger than 45 will work.

Case 2: When I call a system that uses the Telebit T1600 modems, I cannot make
a connection if the ATI modem is set to use V.42bis or MNP5. The ATI modem
will only connect reliably when it is set to use MNP4.

Solution: To connect successfully, I have to set up the modem as V.32 with
MNP4 by sending the string AT&F1&U0 to the ATI modem. (AT&F1 sets the ATI
modem as V.32 with MNP5, &U0 turns off data compression.)

2. Your communication software may not be compatible with the setting.

For example, America Online implemented an errorcorrecting scheme in the
software (both the PC and the Mac versions) which is not compatible with the
modem's error correction protocol.

Solution: To use America Online, you need to turn off error control on the
modem. AT&F configures the ATI modem as V.32 without error control.

3. Your computer hardware may not work with the setting. As I mention earlier,
you need a properly wired cable for the Mac to use hardware flow control. If
you do not have the right cable or if your Mac simply won't work with the
cable, you will need to use software flow control. (&K4 tells the ATI modem to
use software flow control.)

Solution: To use the ATI modem in V.32/V.42bis mode with my Mac, I need to
disable hardware flow control and use XON/XOFF software flow control instead.
The initialization string AT&F2&K4&C1&D2S7=60 sets up the modem properly
(again, S7=60 is for calling the Hayes BBS).

4. You may need to change the setting to achieve better performance. It is
advisable that you turn off MNP5 while downloading precompressed files from a
remote system that has a MNP5 modem. You can initialize the ATI modem to turn
off MNP5 data compression with the string AT&F1&U0.

Again, the initialization string used here is for the ATI modem only. If you
use a different modem, you would need to check with the modem manual to find
out the equivalent commands to use.

VIII.5. Editing the Initialization String

If the initialization string provided by your software does not work (or if
your software does not support your modem at all), you'll need to edit the
initialization string in your communications program.

The modem initialization string consists of a series of commands (called the
AT commands). They can be divided into three groups:

1. A capital character followed by a digit. For example, M1.
2. An ampersand & and a capital character followed by a digit. For example,
   &M1. Note that M1 is different from &M1.
3. Sr=n where "r" is the number of the register to be changed and "n" is the
   new value that is being assigned. For example, S7=60.

There are some other characters that may also appear in the modem
initialization string. These characters normally should not be changed.

AT      tells the modem that modem commands follow.

Z       resets the modem to default state

~       makes your software pause for half a second. You can use
        more than one ~ in a row. For example, ~~~~ tells the
        software to pause two seconds.

^M      sends the terminating Carriage Return character to the
        modem. This is a control code that most communication
        software translate as a "carriage return."

Let's assume that the appropriate initialization string to use is
AT&F2&C1&D2S7=60 (for the ATI modem). You'll need to replace this string with
the one provided by your communications software.

If your software does not support your modem, you can install the program by
telling it that you have a Hayes modem.  After the installation, you'll simply
edit the initialization string with the appropriate one. Please make sure you
do not delete any ~ or ^M.

Here are some examples,

1. To change the string provided by Procomm Plus
        ATE1 S7=60 S11=60 V1 X1 Q0 S0=0^M

Use the string
        AT&F2&C1&D2S7=60^M

2. To edit the string used by Telix
        ATZ^M~~~AT S7=45 S0=0 V1 X4^M

change it to
        ATZ^M~~~AT&F2&C1&D2S7=60^M

3. To replace the initialization string provided by ZTerm (Macintosh)
        ATE1M1 V1^M

use the following string
        AT&F2&C1&D2S7=60^M

VIII.6. Match Software Settings to the Modem Settings

Besides using the right initialization string, you also need to make sure that
the settings in your communications program match those of the modem.

VIII.6.a.       Speed setting

If you have a modem that supports data compression. You want to make sure that
the speed setting for the entries in your dialing directory is the maximum
throughput. Here are the general rules of thumb:

For a V.32bis/V.42bis modem, set speed to 38400 or 57600 bps (check your modem
manual). For a V.32/V.42bis modem, set speed to 38400 bps. For a V.32/MNP5
modem, set speed to 19200 bps. For a V.22bis/V.42bis modem, set speed to 9600
bps. For a V.22bis/MNP5 modem, set speed to 4800 bps.

Note: Your computer may not be fast enough to work reliably at 38400 or 57600
bps. Also, the communications programs you use may not support speed higher
than 19200 bps.

VIII.6.b.       Hardware flow control

Note that you will need to configure your software to use hardware handshaking
if the modem is initialized to use hardware flow control.

VIII.6.c.       Dialing Timeout Value

Independent from your modem setting, your software may also impose a limit on
how long it will wait for a connection. If you initialize the modem with the
command S7=60, you'll need to change the timeout value used by your software
to 60 seconds accordingly.

IX.     Configuring Popular Communications Software

Below are brief instructions for configuring some popular communications
programs to work with a high-speed modem. The particular initialization string
is for the ATI 9600etc/e modem. It is assumed that the appropriate
initialization string to use is "AT&F2&C1&D2S7=60" if you are using a PC. (Use
"AT&F2&C1&D0S7=60" if you have a Macintosh.)

Make sure you save the changes you make.

IX.1.   Procomm Plus 2.0

To change the modem initialization string: (Global, i.e. it works with every
dialing entry)

1. Load Procomm, press Alt-S
2. Select Modem Options
3. Select Modem Commands
4. Press A
5. Change the initialization string to
        AT&F2&C1&D2S7=60^M

To set the software to wait 60 seconds for connection: (Global)

1. Load Procomm, press Alt-S
2. Select Modem Options
3. Select General Options
4. Press A
5. Type 60 and press Return

To enable hardware flow control: (Global)

1. Load Procomm, press Alt-S
2. Select Terminal Options
3. Press D (hardware flow control)
4. Press Space Bar to toggle, press Return to accept
5. Press C (software flow control)
6. Press Space Bar to toggle, press Return to accept

IX.2.   Telix

To change the modem initialization string: (Global)

1. Press Alt-O
2. Select Modem and dialing
3. Select A (Init String)
4. Change the initialization string to
        ATZ^M~~~AT&F2&C1&D2S7=60^M

To set the software to wait 60 seconds for connection: (Global)

1. Press Alt-O
2. Select Modem and dialing
3. Select K (Dial time) and enter 60 press Return

To enable hardware flow control (Global)

1. Press Alt-O
2. Select Terminal options
3. Press J (XON/XOFF software flow control)
4. Select Off
5. Select K (CTS/RTS hardware flow control)
6. Select On
7. Press ESC to exit

IX.3.   Qmodem

To change the modem initialization string: (Global)

1. Press Alt-N
2. Press M to select Modem menu
3. Select Modem Commands
4. Press Return
5. Change the initialization string to
        AT&F2&C1&D2S7=60^M

To set the software to wait 60 seconds for connection: (Global)

1. Press Alt-N
2. Press M to select Modem menu and Press Return to select Communication
   Parameters
3. Press H to select Timeout delay
4. Type 60 and press Return
5. ESC to exit

To enable hardware flow control: (Global)

1. Press Alt-N
2. Select Toggles
3. Press Return to toggle XON/XOFF flow
4. Select CTS/RTS flow
5. Press Return to toggle
6. ESC
7. ESC
8. Press E for Exit
9. Save Changes

IX.4.   HyperAccess 5

Note: HyperAccess 5 supports the ATI 9600etc/e. However, HyperAccess 5 does
not let you edit the initialization string directly. You can add additional
setup commands to change the modem settings for each individual dialing entry.

To change the modem initialization string: (Individual, i.e. it works only
with the particular dialing entry)

1. Select Define system settings from the Main menu
2. Select Modify
3. Use cursor to select the system to modify and press Enter
4. Select Hardware from the System settings menu
5. Select Modem
6. Select Additional modem setup commands
7. Type S7=60
8. Press ESC twice to go back the Main menu

To set the software to wait 60 seconds for connection:

N/A

To enable hardware flow control: (Individual)

1. Select Define system settings from the Main menu
2. Select Modify
3. Use cursor to select the system to modify and press Enter
4. Select Hardware from the System settings menu
5. Make sure that Data terminal ready signal is output on DTR, delete RTS if
   it is listed
6. Select Communications port
7. Select Incoming hardware handshaking and type CTS
8. Select Outgoing hardware handshaking and type RTS

IX.5.   Crosstalk for Windows

To change the modem initialization string: (Global)

1. Pull down Setup menu and select Modem...
2. Select Custom and click on Settings
3. Change the initialization string to
        ^M~AT&F2&C1&D2S7=60^M
4. Click OK

To set the software to wait 60 seconds for connection: (Individual)

1. Pull down File menu and select Open a phone book entry
2. Open the phone book entry
3. Pull down Setup menu and select Session
4. Click on More
5. Change the value in Allow xx seconds for the host to answer

To enable hardware flow control: (Individual)

1. Pull down File menu and select Open a phone book entry
2. Open the phone book entry
3. Pull down Setup menu and select Device
4. Click on RTS/CTS and click OK

IX.6.   MicroPhone II (Mac)

To change the modem initialization string: (Individual)

1. Choose Settings Menu
2. Select Communications
3. Choose V.32 Standard from the Modem Driver list box
4. Click OK
5. Hold down the Command key and choose Scripts menu
6. Select Modify Script
7. Click the Modem Scripts button
8. Double-click on Modem_Init
9. Double-click on the first line that says
        Set Variable * mcmd from Expression "'AT....'"
10. Change the initialization string in the lower right box to
        'AT&F2&C1&D2S7=60^M'
11. Double-click on the second line that says
        Set Variable * mcmd from Expression "'AT....'"
12. Change the initialization string in the lower right box to
        'AT&F2&C1&D0S7=60^M'
13. Click OK
14. Press the Option key and choose the File menu
15. Select Save Modem Driver (If you want to save the driver under a new name,
    select Save Modem Driver As... in the File Menu. Name the new driver, and
    save it into the Modem Folder.)

To set the software to wait 60 seconds for connection:

N/A

To enable hardware flow control: (Individual)

1. Pull down Settings Menu
2. Select Communications
3. Click on the Hardware Handshake box

IX.7.   White Knight (Mac)

To change the modem initialization string: (Global)

1. Choose Local Menu and select Serial Port
2. Choose Modem Init Command to
        AT&F2&C1&D0S7=60

To set the software to wait 60 seconds for connection: (Global)

1. Choose Service Menu and select Dial or Redial Number
2. Change the value in Wait for Answer up to XX seconds to 60

To enable hardware flow control: (Global)

1. Choose Local Menu and select Serial Port
2. Check Use Hardware Handshake

IX.8.   ZTerm 0.85 (Mac)

To change the modem initialization string: (Global)

1. Choose Settings Menu and select Modem
2. Change Init String to
        AT&F2&C1&D0S7=60^M

To set the software to wait 60 seconds for connection: (Global)

1. Choose Settings Menu and select Modem
2. Edit Dial Timeout

To enable hardware flow control: (Individual)

1. Choose Settings Menu and Select Flow Control
2. Uncheck Xon-Xoff Receive
3. Uncheck Xon-Xoff Send
4. Check HW Handshake

X.      Other Settings for Your Communications Software

X.1.    Telephone Number

Online services use different phone numbers for different kinds of modems. To
get the best throughput, make sure  you dial the right phone number. Note that
many bulletin board systems do not allow calling their high-speed modem lines
with 2400 bps modems. You would be disconnected.

For example:

EXEC-PC, the largest BBS in the United States, has the following telephone
numbers:

#1: Standard 2400 bps modems                            414-789-4210
#2: US Robotics HST 9600 MNP5                           414-789-4337
#3: US Robotics HST 14400                               414-789-4352
#4: Boca BocaModem V.32bis/V.42bis                      414-789-4360
#5: CompuCom Speedmodem 9600 MNP modems                 414-789-4450
#6: Hayes 9600B Vseries modems, NON-V.32                414-789-4315

If you have a 9600 bps HST modem, call #2.
If you have a 14400 bps HST modem, call #3. You can also call #2 but you won't
be able to get the best throughput.
If you have a V.32 modem, call #4.
If you have a V.32bis modem, call #4.
If you have a CompuCom SpeedModem Champ, call #5
If you have a CompuCom SpeedModem Storm, call #4 (V.32), #5 (CSP)
If you have a CompuCom SpeedModem Star, call #4 (V.32bis), you can also call
#5 (CSP) but you can only connect at 9600 bps.
If you have a Hayes Vseries Smartmodem 9600 (or 9600B) modem, call #6.

X.2.    Dial String: ATDT

You don't have to change the dialing string unless you use a PBX system or
have call waiting service.

X.2.a.  PBX

If you have to dial the digit 9 to obtain an outside line, Use
ATDT9,<<number>>. The comma (,) instructs the modem to pause two seconds. This
allows enough time for the dial tone to occur before the modem dials. You can
use as many commas as you like.

X.2.b.  Call Waiting

Call waiting service will disrupt modem sessions. If your telephone company
supports the ability to disable call waiting, use the dial string
ATDT*70,<<number>> (make sure you add the comma ,) instead of just
ATDT<<number>>.

        ATDT*70,1234567

Also, adding 1170 after the ATDP dial command can be used to disable
callwaiting on some pulsedialing phone systems. Check with your phone company
to see if these features are supported.

X.3.    8-N-1 or 7-E-1 (data bits, parity, stop bits)

In general, set the parameters to 8-N-1. If you are calling a commercial
online service (such as GEnie), you may need to set the parameters to 7-E-1.

X.4.    Half vs. Full Duplex

The only popular online service that uses half duplex is GEnie.

X.5.    Terminal Emulation

If you are using an IBM compatible, choose IBM PC or ANSI. Otherwise, try
VT102, VT100, VT52, TTY.

X.6.    Comm Port

For your computer to talk to your modem, you need to tell the software where
to find the modem. If you use a PC with an external modem, you need to specify
which serial port the modem is connected to. If you have an internal modem,
you need to configure the modem and tell the software which COM port the modem
is configured for.

If you use a Macintosh, specify whether your modem is connected to the modem
port or the printer port.

X.7.    File Transfer Protocols

Errors that occur during file transfer are automatically detected and
corrected by file transfer protocols. If a block of data is received
incorrectly, the receiving system sends a message to the sending system and
requests the retransmission. This process is automatic. When errors occur
during file transfer, the communication program shows an error in the file
transfer status window.

X.7.a.  ASCII

This is designed to work with ASCII text files only. Notice that you do not
have to use this protocol when transferring text files. The ASCII protocol is
useful for uploading a text file when you are composing e-mail online.

X.7.b.  Xmodem

Xmodem is one of the most widely used file transfer protocols. The original
Xmodem protocol uses 128-byte packets and a simple "checksum" method of error
detection. A later enhancement, XmodemCRC, uses a more secure Cyclic
Redundancy Check (CRC) method for error detection. Xmodem protocol always
attempts to use CRC first. If the sender does not acknowledge the requests for
CRC, the receiver shifts to the checksum mode and continues its request for
transmission.

X.7.c.  Xmodem-1K

Xmodem-1K is essentially Xmodem CRC with 1K (1024 byte) packets. On some
systems and bulletin boards it may also be referred to as Ymodem. Some
communication software programs, most notably Procomm Plus 1.x, also list
Xmodem-1K as Ymodem. Procomm Plus 2.0 no longer refers to Xmodem-1K as Ymodem.

X.7.d.  Ymodem

Ymodem is essentially Xmodem-1K that allows multiple batch file transfer. On
some systems it is listed as Ymodem Batch.

X.7.e.  Ymodem-g

Ymodem-g is a variant of Ymodem. It is designed to be used with modems that
support error control. This protocol does not provide software error
correction or recovery, but expects the modem to provide the service. It is a
streaming protocol that sends and receives 1K packets in a continuous stream
until instructed to stop. It does not wait for positive acknowledgement after
each block is sent, but rather sends blocks in rapid succession. If any block
is unsuccessfully transferred, the entire transfer is canceled.

X.7.f.  Zmodem

This is generally the best protocol to use if the electronic service you are
calling supports it. Zmodem has two significant features: it is extremely
efficient and it provides crash recovery.

Like Ymodem-g, Zmodem does not wait for positive acknowledgement after each
block is sent, but rather sends blocks in rapid succession. If a Zmodem
transfer is canceled or interrupted for any reason, the transfer can be
resurrected later and the previously transferred information need not be
resent.

X.7.g.  Kermit

Kermit was developed at Columbia University. It was designed to facilitate the
exchange of data among very different types of computers (mainly minicomputers
and mainframes). You probably will not need to use Kermit unless you are
calling a minicomputer or mainframe at an educational institution.

X.7.h.  Which file transfer protocol should you use?

In general, I recommend Zmodem. If Zmodem is not supported by the system you
are calling, use Ymodem-g. (If you are connecting to a UNIX system in a
university, you may have to use Kermit or Xmodem to transfer files.)

Here are the test results obtained by downloading the files using various file
transfer protocols. The number before the parentheses is the transfer speed
(in cps) and the number in the parentheses is the time elapsed (in seconds).

Filename        Xmodem     Xmodem1K     Ymodem     Ymodem-g     Zmodem
-------------------------------------------------------------------------
the-wave.txt    429(334)   1508(95)     1527(94)   3261(44)     3296(43)
dayrpt.arc      314(26)     758(11)      761(11)   1042(8)      1025(8)
dayrpt.wks      415(47)    1252(15)     1244(15)   2314(8)      2337(8)
sunset.arc      337(15)     771(6)       745(6)     987(5)       965(5)
sunset.pic      399(41)    1337(12)     1297(12)   2594(6)      2588(6)
text109k.arc    343(86)     817(36)      814(36)   1089(27)     1064(27)
text109k.txt    410(271)   1379(80)     1351(82)   2812(39)     2885(38)


=============================================================================

Appendix A:     Resources

1. Modem Manufacturers

Here is a list of selected modem manufacturers.

Manufacturer            Information     Tech Support     Support BBS
-------------------------------------------------------------------------
ATI Technologies        [phone]  [phone]  [phone]
Cardinal                [phone]  [phone]  [phone]
Compucom                [phone]  [phone]  [phone]
Hayes                   [phone]  [phone]  [phone]
Image Comm.             [phone]  [phone]  n/a
Intel                   [phone]  [phone]  [phone]
Microcom                [phone]  [phone]  [phone]
MultiTech               [phone]  [phone]  [phone]
Practical Peripherals   [phone]  [phone]  [phone]
Prometheus              [phone]  [phone]  [phone]
Supra                   [phone]  [phone]  [phone]
Telebit                 [phone]  [phone]  n/a
U.S. Robotics           [phone]  [phone]  [phone]
Zoom                    [phone]  [phone]  [phone]


2. Support BBS for Software

Here are the support BBS for popular communications software.

Software                                                Support BBS
-----------------------------------------------------------------------
Procomm Plus (Datastorm Technologies, Inc.)             [phone]
Telix (Exis Inc.)                                       [phone]
Qmodem (The Forbin Project, Inc.)                       [phone]
HyperAccess 5 (Hilgraeve Inc.)                          [phone]
Crosstalk for Windows (DCA)                             [phone]
MicroPhone II (Software Ventures)                       [phone]
ZTerm (David Alverson)           via CompuServe, GEnie, America Online


=============================================================================

Appendix B.     How to reach the author

     If you have any comments or suggestions, I'll love to hear from you.
     You can reach me in many ways:

     America Online:         Pat Chen

     CompuServe:             70754,3162

     GEnie:                  p.chen2

     Internet:               [e-mail]
                             [e-mail]

     MCI Mail:               445-6669

     U.S. Mail:              Patrick Chen
                             P.O. Box 5325
                             Irvine, CA 92716
                             USA

==============================================================================

Appendix C: What is "The Joy of Telecomputing"?

     "The Joy of Telecomputing" is a 200-page, three-part book/report
     consisting of the following articles: "What you need to know about
     modems,""Life beyond CompuServe" and "Is AT&T the right choice?"

     Going online has become a way of life for many computer users. It is
     undeniably fascinating, fulfilling and fun. But there is also a down side
     to it: the cost can be prohibitive. I have yet to meet an avid modem user
     who didn't wish that he could afford to be online longer.

     To get the most mileage from your online dollars, you need to know the
     answers to the following three questions:

     *  What is the right modem to use?
     *  What online services are available and how do they compare?
     *  What is the most cost-effective way to reach those services?

     These are not isolated questions. The answers to these questions will help
     you decide what online systems are right for you.

     "The Joy of Telecomputing" is a practical guide to the online world.
     Its goal is to help you get the most from telecomputing. The goal is not
     to tell you that so-and-so is the best for you, but to present you with
     enough information so that you will be able to determine what is right for
     you.

     The discussions in "The Joy of Telecomputing" are devoted to the following
     online activities: file transfer (downloading shareware, exchanging files
     with colleagues or friends), electronic mail, conferences (forums,
     newsgroups, SIGs). You won't find discussions on stock quotes, shopping
     malls, online databases, etc.

     The online world is constantly changing and it will remain one of the
     hottest growing area in microcomputing for many years to come. "The Joy of
     Telecomputing" is an ongoing project. It is being constantly updated to
     provide you the information you need on a timely basis.


=============================================================================

Appendix D: What's in "Life Beyond CompuServe"?

     Part II of "The Joy of Telecomputing" provides a comprehensive survey of
     the online world. It covers the three major groups of online systems:

     * Commercial online services (America Online, BIX, CompuServe, DELPHI,
       GEnie, MCI Mail, Prodigy, etc).
     * BBS (including discussions on FidoNet, RIME, etc)
     * The Internet (including discussions on UUCP, Usenet, Bitnet, etc).


     1. Commercial Online Services

     In general, commercial online services do not offer good
     price/performance, though some of them excel in certain areas (such as
     e-mail). We'll look at the major commercial online services (CompuServe,
     GEnie, Prodigy, etc.) and see what they offer and what they are good
     for. Major topics covered are:

     * What are the major commercial online services?
     * How much do they cost?
     * How can you access those services?
     * What do they offer? How do they compare with each other?
     * How do they compare with BBS?


     2. The World of BBS

     It is estimated that more than 30,000 bulletin boards exist in the
     United States. If you live in a metropolitan area, you'll probably find
     hundreds of BBS that are local. Most BBS operate as a hobby by their
     owners and without charge to their users. There are many BBS that have
     members all over the United States (and the world).

     The world of BBS has become a phenomenon. BBS are no longer isolated
     systems. Fidonet, the network linking thousands of BBS around the world,
     allows users on one BBS to communicate with those on other BBS.
     Recently, with gateways to the UUCP network, many BBS has allowed their
     members to exchange e-mail with users of the Internet and to participate
     in Usenet newsgroups.

     We'll cover the following topics:

     * How many BBS are there? How do they compare?
     * How much does it cost to become a member?
     * What are the limitations?
     * How to find BBS numbers?
     * Which BBS offers the latest and greatest files for PC users?
       Macintosh users? Amiga users?
     * Which BBS are good for chatting? Which are good for conferences?
     * What is Fidonet? How does it work? What does it offer?
     * How to join Fidonet as a node?
     * How to become a point on Fidonet?
     * How to send e-mail from Fidonet to Internet (and from Internet to
       Fidonet)?
     * What is RIME?
     * What are the major BBS software available?
     * How to use BBS effectively?
     * What software tools you need and where to find them?
     * BBS Etiquette
     * Why ZTerm is the best program to use for calling BBS? (For Macintosh
       users only)
     * What are MacBinary files? How to download a Macintosh file to a PC?
       How to download a PC file to a Macintosh? (For Mac users or people
       who use both Mac and PC.)


     3. Internet

     Internet is a global computer network linking hundreds of thousands of
     computers (mainly UNIX computers) at universities, research institutions
     and government agencies. Internet is unsurpassed for e-mail and
     conferences (called newsgroups in the UNIX world). It is also an
     invaluable resource for free software. Some major topics covered are:

     * What is Internet
     * What is UUCP? What is Usenet? What is Bitnet?
     * What can you do on the Internet
     * How to send e-mail on the Internet?
     * How to send e-mail from Internet to CompuServe, MCI Mail, Fidonet
       (and vice versa)?
     * How to send binary files?
     * What newsgroups are available?
     * How to participate in a newsgroup?
     * Etiquette
     * What is FTP?
     * What is Anonymous FTP?
     * How to use FTP?
     * What are the FTP sites available?
     * How to find the files you need?
     * What is telnet?
     * What can you do with telnet? (Read "The Cuckoo's Egg" by Cliff Stoll
       for a first-hand account on how a German hacker use telnet to break
       into computers on Internet.)
     * How to use telnet?
     * How can you get an Internet account?
     * What services are available? What kind of access level do they offer?
     * How much do they cost?
     * How to transfer files from a UNIX host to your personal computer?
     * What are uuencode and uudecode?
     * What are compress, tar and shar?

=============================================================================

Appendix E: What's in "Is AT&T The Right Choice?"

     Part III of "The Joy of Telecomputing" provides detailed discussions on
     the various ways you can reach a remote system (i.e., a system which is
     not local to you). What is the most cost-effective way to reach those
     systems?

     There are generally two options you have to reach a remote system:

     1. You can place a distance call using AT&T, MCI, etc.
     2. You can reach the system via some packet-switching networks by
        dialing a local number (the system you are calling may already have a
        deal with a packet-switching network and charge you accordingly, or
        you may subscribe to one of the packet-switching networks yourself).

     (If you are trying to reach a remote Internet host, you have one more
     option. You can log in to a local host on the Internet and then use telnet
     to access the remote host.)

     However, packet-switching networks differ widely in what they offer, how
     much they charge, and how well they perform. We'll look at some of the
     services available (PC Pursuit, Connect-USA, Accu*Link, Tymnet,
     REDI-Access, etc.).

     * How many ways can you reach a remote system? What are the pros and
       cons?
     * What are packet-switching networks?
     * How do they work?
     * What services are available?
     * What do they offer?
     * What kinds of modems do they support?
     * What are the differences in performance among different
       packet-switching network?
     * How much do they cost?
     * Are packet-switching networks cost-effective?


=============================================================================

Appendix F: Updates, bulletins, and tutorial articles

     "The Joy of Telecomputing" will be updated on a regular basis. If you
     order the book, you'll receive future updates automatically and free of
     charge as long as you have an e-mail address that can be reached from the
     Internet. Note that you don't need to have an account on an Internet host.
     If you are using an online service that have an Internet gateway (e.g.
     CompuServe, MCI Mail, America Online), you can receive e-mail from the
     Internet.

     In addition to the quarterly update, you'll also receive bulletins from
     time to time. To receive the updates and bulletins, please send your
     e-mail address to  [e-mail] with a subject line of
     "subscribe" (please include your name and/or company name in the body of
     the message).

     Besides updates and bulletins, there will be tutorial articles available.
     If you are new to the Internet, for example, you may need some
     hand-holding in learning to use the UNIX mail, elm, rn, etc. These
     articles should be available by the end of June. Unlike the updates and
     bulletins, these articles won't be sent automatically. To get a list of
     the articles, please send e-mail to [e-mail] with a subject
     line of "tutorials". You'll recive the list and the instruction for
     requesting the articles you want (if there is a topic that you'll like to
     have an article written, please send e-mail to [e-mail]).

     For those of you that don't have an e-mail address reachable from the
     Internet, I'm planning to set up a BBS in the future (hopefully before the
     end of 1992). You'll be notified when the BBS is available.


=============================================================================

Appendix G: How to order "The Joy of Telecomputing"

     30-Day Money-Back Guarantee:  If you are not satisfied with your purchase
     of "The Joy of Telecomputing," return it in resalable condition with all
     the original packaging within the guarantee period for a refund check.
     Shipping cost is not refundable.

     To order a printed copy of "The Joy of Telecomputing," send a check or
     money order to the following address:

          Patrick Chen
          PO Box 5325
          Irvine CA  92716
          USA


          "The Joy of Telecomputing"                              $19.95
          Shipping and Handling (see below)                       $_____
          California residents please add 7.75% tax ($1.55)       $_____

                                                     Total        $_____

     Note: Shipping and handling fee is $5 within the United States; $10 to
     Canada, Mexico, Puerto Rico, and Central America; $15 to Europe,
     Australia, and Asia. Please allow 2-4 weeks for delivery.

     Non-US residents:  please send checks or money orders drawn on US Banks in
     US Funds.

     There is no need to fill out the order form if you are sending a check
     with your name and address printed on it.


     Name:
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     E-mail Address:

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     MCI Mail: ______________________ Genie: ______________________________

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