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Filename : 9600-INF.TXT

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PURPOSE: To translate Advertising and misinformation about 9600 bps
modems into everyday BBS talk. There is a lot of confusion
about 9600bps communications and I'll attempt to explain,
clarify and define some of the terms and claims you'll encounter
when purchasing a high speed modem.

DISCLAIMER: The information presented was accurate at the time this file
was written, but with the way the world moves, it might not be
true when you read this. I will not be responsible for damages
or losses incurred if you depend solely on this file for your
information. I encourage you to investigate any claims either I
or a manufacturer/dealer makes.

CORRECTIONS: If I made an error, do not modify this text. Add a file to the
ZIP with your comment/correction/opinion and re-ZIP the file.

I am a SysOp of a BBS in Los Angeles, CA that runs multiple 9600+ bps lines.
I also compile and distribute the 96LIST (a list of BBS's that support 9600+
bps CONNECTs). I am not a modem guru and I learn more about modems daily. I
have used a number of different 9600 bps modems that include USR HST's, Hayes
V-series, v.32, v.32bis and Telebit Trailblazers [PEP]) both on my BBS and as
a user.

I monitor the USR, v.32 and Hayes conferences on Intelec, SmartNet and
U'NInet. During the gathering of information for 96LIST and attempting to
stay on top of what's new, I've seen some of the most commonly asked
questions people ask when shopping for high speed modems and will attempt to
incorporate those questions and answers into this file.

In this file, I will try to give you the good and bad points of each modem as
I see them. Whatever brand or type modem you buy is up to you. Research your
prices well and investigate, investigate, investigate! Learn to separate the
hype from the facts.

Ken Sukimoto

Without getting too techy, the best way to decide which one to get is to make
a list of the BBS's you call and then:

1. Note what kind of modem they use (v.32, HST, Hayes, etc)
2. Take a look at your budget and see what you can afford.
3. Check your hardware and make sure it will handle 9600 bps.
4. Buy the modem that is the most compatible with your equipment, the
greatest number of BBS's you call and that fits in your budget.
5. If the budget will handle it and you've chosen a proprietary modem,
try and stretch the budget to get a dual standard model for cross brand
6. Live with your decision - but don't put down someone elses choice if
it was different than yours.
7. Enjoy! And encourage others to upgrade to 9600!

Much has been said of "Standards".

"Is it Hayes compatible? They're the 'Standard'"

Not necessarily true when we talk of 9600 (and greater).

Hayes established a Standard for the AT command set. Other modem
manufacturers adopted this standard for the commands their modems would
recognize. But if you look at your current modem specification sheet, you
will see a different set of standards for the method that your modem
communicates at 300 bps, 1200 bps and 2400 bps - no mention of Hayes.

The current talk is, "HST is the standard for 9600!" Untrue, it is the
most widely used method in the BBS community, but it is proprietary - not
available to other companies (more on this later). Much like IBM's MCA
bus, it might be good - but you have to buy IBM to get it (but even IBM
licenses MCA to other companies).

My personal opinion is that the CCITT v.32 and v.32bis are THE Standards -
maybe not the most widely used today, but in the forseeable future. This is
because the CCITT standards are a published guidelines available to all modem
manufacturers to implement. They may not be the fastest, but they are a
common method - promoting maximum connectivity.

First, let's get this clear - although everyone seems to use the terms "Baud"
and "Bps" interchangably, there is a difference. A baud is one cycle change
during the transmission of data over the modem. During that one cycle change,
a number of bits can be sent. The one instance where BAUD=BPS is when a
transfer is occuring at 300 Baud. 300 Baud is defined as 300 cycle changes per
second with one data bit being sent during each cycle change. Higher BPS rates
are achieved by sending multiple data bits at 300 Baud (cycle changes), 600
Baud and 2400 Baud. 9600 bps speeds are achieved by using 2400 Baud (cycle
changes) with 4 data bits per cycle change. Technically, a 2400 Baud modem is
most likely a 9600 bps modem and there is no such modem as a 9600 Baud modem.
I only bring this up to pick a nit and to let you know that I am aware there
is a difference. Also to give you a sense of being in on a secret and giving
you the chance to win a bet at the office.

What is MNP, v.32, v.42?
You've probably seen those v.XX numbers and wondered what they all meant.

These standards are dictated by the CCITT, an international council composed
of national agencies and major manufacturers. The numbering can be confusing
as each standard is a separate one (except when it applies to a second or
third generation standard - designated with a "bis" or "tres" suffix). A
higher number does not necessarily mean better and may not even apply to the
same function as a lower number.

As a general rule of thumb, the v.22 series refers to CONNECT methods for
speeds of 1200 bps to 2400 bps. The v.32 series standards apply to 9600+ bps
CONNECT methods. Within each of these numbers series, you might see "bis"
suffixes. These designate the second generation of that number series and
means an enhancement to the basic standard.

V.32 is an international 9600 bps standard for communicating at 9600 bps
that can be implemented by modem manufacturers without licensing fees. V.32
uses full duplex modulation (9600 bps in both directions at once). The full
duplex method is advantageous when data in equal amounts is being sent in
both directions simultaneously, such as in an interactive application or when
(and if) BiModem or another bidirectional protocol gains favor. V.32 also
incorporates fallback rates of 7200 bps and 4800 bps when line conditions
prevent a reliable 9600 bps CONNECT rate.

V.32bis is the second generation of v.32 and calls for a CONNECT rate of
14,400 bps with a fallback rate of 12,000 bps. In order to be v.32bis
compliant, the modem must also be v.32 compliant. v.32bis is also full duplex
by specification. There are currently several v.32 modems that are v.32bis
COMPATIBLE because they include the v.32bis fallback 12,000 bps rate. These
particular modems are not v.32bis COMPLIANT since they do not include the
14,400 bps rate.
V.42 is an international CCITT standard for data compression. V.42
incorporates downward compatibility with Microcom (c) Network Protocol (aka
MNP) Levels 1 to 4 error correction. It also includes LAPM (Link Access
Procedure for Modems) which uses Cyclic Redundancy Checking (CRC) to ensure
data reliability, as does MNP level 4.

V.42bis is the second generation of v.42. Besides v.42, it also incorporates
intelligent data compression where it can detect if the file has already been
compressed and would not benefit from further compression. If the file would
benefit from compression, v.42bis could optimally deliver a 4:1 compression
factor. This is the often cited reason for claiming a 38,400 bps throughput
on an otherwise 9600 bps CONNECTion. There are 2400 bps modems that have
v.42bis as a feature and these manufacturers and dealers have sometimes
(erroneously) advertised their modems as 9600 bps modems (with "throughput"
added as an afterthought and in small print). If v.42bis detects the file
would not benefit from data compression, it will politely step aside and send
the file without wasting time trying to compress it anyway.

NOTE: Although v.32 and v.42 share the v.# numbering and are CCITT standards,
they are independent of each other. Having one does not mean you have
the other. Because a modem incorporates v.42 does not mean it has v.32
or vice versa. Unless assured otherwise, you should view each v.x as an
independent standard.

View the v.22 and v.32 categories as METHODS OF CONNECTION and the
v.42 category as an OPTIONAL FEATURE available to the methods of

It is entirely possible to have a v.22bis (2400 bps) modem [METHOD OF
CONNECTION] and v.42bis [OPTIONAL FEATURE] as well as a v.32bis modem
[METHOD OF CONNECTION] without v.42, MNP or v.42bis [OPTIONAL

MNP [Microcomm (c) Network Protocol] levels 1 to 4 are methods of error
correction where the two connected modems perform the verification of data
sent & received. There are software emulators of MNP, but I have not tested
them. Error correction is a requirement of streaming protocols such as
Ymodem-G where the protocol just sends a constant stream of data and lets the
modems do the error correction. This also requires a clean, noise free line
as streaming protocols will abort if line noise interferes too much.

MNP Level 5 is for data compression. As most BBS's archive their files or
files are already in a compressed format (demonstrate this by trying to ZIP a
GIF file), MNP5 can actually increase the overhead by attempting to compress
the file further. That is why you should ask if throughput claims are arrived
at by using data compression techniques - you will usually not have MNP5
enabled when you are transferring compressed files on most BBS's. When MNP
Level 5 is of use on an uncompressed file, it can achieve a 2:1 compression
factor; doubling the apparent throughput of the actual CONNECT rate.

During your modem shopping and later when viewing BBS ads, you'll see figures
of 19,200bps and 38,400bps tossed around. As mentioned above, special data
compression methods enable higher transfer rates on qualified files. In order
for this data compression phase to work, the speed your computer (Data
Terminal Equipment - DTE) and your modem (Data Communications Equipment -
DCE) must be higher than the actual link rate between the two connected
modems. The data moves from the sending computer at this rate and if it is
able to be compressed, either MNP 5 or v.42bis will do so and the data will
be sent over the phone lines to the receiving modem at the link rate - NOT
the DTE/DCE rate. The receiving modem will then reverse the process and
uncompress the data and send the received data to the receiving DTE at the
higher DTE/DCE rate at that end. This perceived THROUGHPUT is achieved at the
link rate - the higher DTE/DCE rate is required at both ends of the
connection, but is NOT the rate the data is travelling between the two modems.

It is entirely possible to have a DTE/DCE rate of 38,400bps on both ends and
if the modems are 2400 bps with no data compression capabilities, there is NO
gain achieved over a 2400 bps modem with a 2400bps DTE/DCE rate. Also, a
9600bps modem with a DTE/DCE rate of 38,400 is not faster than a 14,400bps
modem with a DTE/DCE rate of 19,200bps. There are entirely too many sysops
who use this ploy either through ignorance, making an attempt to impress
the unknowing with big numbers or attempting to hide a lower link rate modem
behind the facade of a high DTE/DCE rate normally associated with a higher
speed modem.

When you call a BBS that is using a modem that has MNP or v.42, you can be
reasonably sure the DTE/DCE rate is at 19,200 or 38,400bps unless you are
told otherwise. As stated previously, most BBS files are not good candidates
for the compression that can take advantage of the high DTE/DCE rates.
Furthermore, not all serial ports or software applications are capable of
supporting the 38,400 bps DTE/DCE rate. The loss of speed between 19,200 and
38,400bps DTE/DCE rate is virtually nil and should not be a cause for major

Bottom line, the DTE/DCE rates and throughput figures should be noted, but in
most all case, is insignificant since it might not even apply in everyday BBS

The items that SHOULD be of concern are the method of CONNECTION and the link
SPEED of that connection.

My own personal viewpoint towards proprietary standards is that since they
_ARE_ proprietary, the support and expandiblity of the system is dependent on
one company and that this is a restriction and disadvantage, regardless of
any performance advantage the proprietary method offers. My one exception to
this opinion is if the proprietary modem also supports the public v.32 or
v.32bis method in addition to the proprietary mode.

CompuCom Corporation's Champ modem is a relatively recent entry in the
9600bps field. This modem uses a half duplex mode of communicating (as do all
the proprietary methods). It's main advantage is very aggressive pricing in
an effort to gain a foothold in an already overcrowded proprietary method
market. Introduced in 1990, not many of the Champ models were sold, even with
the low price. At this writing, the Champ is enjoying some popularity because
of even lower pricing and the impending release of dual standard models that
will support the v.32 or v.32bis method and the CSP method. The Storm model
(CSP and v.32) and the Challenger (v.32bis and CSP) seem to be popular modems
based on preliminary advance orders.

If price is the major concern and compatibility is assured by using the modem
in a closed environment (where the method is prescribed by common agreement
or the purchaser controls the modems used on all connections), the CompuCom
Champ might be the modem of choice.

Hayes Corporation's V-series was one of the early entries in the PC 9600bps
modem market. Along with USR's HST, the V-series was once under consideration
as a candidate for the standard. However, the CCITT dropped both methods from
consideration since they were half duplex - full duplex was and is an
important feature for consideration as an CCITT standard.

In the 9600 bps area, Hayes is comparitively slow in introducing new features
on their modems (as of today, there is no Hayes v.32bis model modem),
however, they are relatively bug free once they start shipping the modems
(based on past experiences).

The V-series Hayes should not be confused with the CCITT v.32 modems. The
V-series is a proprietary method of connection. Hayes does have an Ultra
series of 9600 bps modem. This model supports both the CCITT v.32 method and
the proprietary Hayes V-series. As of this writing, Hayes has announced the
Ultra 14,400 model which includes the Hayes V-series mode and the CCITT
v.32bis mode. They have also introduced a low cost v.32 only modem to compete
with other generic CCITT v.32 modems. Neither were shipping as of the date of
this writing.
Telebit's strongest position is in the Unix environment. The PEP technology
lends itself very well to the types of files transferred over networks using
this Operating System.

The relative scarcity of PEP sites makes this method a poor choice for all
around BBS usage, although the Telebit 2500 is both PEP and CCITT v.32
compliant and might be a candidate if the BBS's or locations you call are
Unix based.
US Robotics was one of the first two companies to offer a proprietary method
of 9600 bps connectivity aimed at the PC market place. Through shrewd
marketting (offering BBS SysOps low cost modems), the current majority of
9600+ bps BBS's are using some type of USR HST method modem.

HST means "High Speed Technology" and is a half duplex method of
communications. Half duplex uses one high speed channel and a much slower
'back channel' for the ACK/NAK signals from the receiver. The high speed
channel switches back and forth, depending on which end has the higher volume
of data to be sent. This half duplex mode is often referred to as
"ping-ponging". Recent models attain higher throughput than 9600 through
optimization of this proprietary method. CONNECT rates of 14,400 bps are
now possible using HST.

US Robotics was the first manufacturer to introduce a modem that supported
both their proprietary technology and the CCITT v.32 9600 bps method, in one
unit. In late 1990, USR introduced their 14,400 bps v.32bis/14,400 bps HST
Dual Standard model. Just recently, USR also introduced a lower priced v.32
9600 model modem as part of their 'Sportster' consumer line. Their other
high end models are known as the 'Courier' models. Although other
manufacturers have introduced or announced 'dual mode' (proprietary AND a
CCITT mode modem) modems, the term "Dual Standard" is a USR copyright.

Each type has advantages and disadvantages. If desktop space and electrical
outlets are at a premium and you are using an IBM compatible PC, an internal
modem might be your best bet. Internal modems also have the advantage of
having the UART the factory recommends on the modem itself. An internal modem
does require a slot on the motherboard (or expansion buss) and draws its
power from the PC power supply. If the number of slots available are in short
supply or if adding another card creates an air circulation problem, this
might make an external modem a better choice. Internal modems usually have a
small speaker for monitoring call progress; depending on the modem and the
location of the modem in the PC, the sound can often be inadequate. Internal
modems reside inside the case and do not offer any signal light capabilities
to help in diagnostics - however, there are some communications programs and
TSR utilities that simulate these lights on the PC screen. Internal modems
are generally configured for which COM port to use by jumpering. No serial
cards are required to install an internal modem. By the same token, if a
serial card is already installed, the corresponding COM port and interrupt on
the serial card must be disabled. One additional problem that might be
encountered is if the communication program locks up. Since the internal
modem draws power from the PC, resetting the modem might involve cold
rebooting the computer to terminate the lock up.

External modems do require desk space and an electrical outlet for the
transformer to provide power. They also require a serial I/O card with the
proper support chips, UART and cable to interface the modem to the PC.
Depending on the case design, air circulation for an external modem could be
better than an internal, the speaker is of usually higher quality and size,
and signal lights are usually incorporated into the case to assist in
diagnosing communication sessions. Since external modems use the common
RS-232 connection, it can be used on other than IBM PC compatible computers.

In 9600 bps modems, there is a lot more configuring to do than 2400/1200
bps modems. A nice feature is a DIP switch (or other hardware) method of
configuring the modem. Saves inputting a 5 line INITialization string. At
the very least, it should have NRAM (Non-volatile Random Access Memory)
that will store your configuration. Several modems have multiple registers
in NRAM that allows storing multiple initialization strings for different
situations. You should also check on internal modems what COM ports are
configurable. Most internal modems can be configured for COM 1 to COM 4 with
the standard interrupts assigned to those addresses. Some modems might be
restricted to COM1 and 2, while better modems might allow full freedom in
assigning COM ports and interrupts.

Your serial port (on internals, it is built on the modem) has a UART
(Universal Asynchronous Receive/Transmit) chip to buffer and control the
Input/Output (I/O). The PC XT usually has an 8450 UART which will handle up
to 9600 bps. The equivalent chip for the AT is the 16450. When you exceed
9600 bps or will be multitasking, you should consider upgrading the UART to
the NS16550AFN UART. This advanced chip is usually available for about $15
and offers a 16 byte buffer to store data that arrives from the sending modem
as incoming data or from the CPU for transmittal. This buffer could be just
enough to solve most common errors associated with high speed communications
and multitasking. It might not be necessary in every instance, but is a
relatively small cost item in view of solving possible future conflicts
and/or problems. When shopping for this chip, the significant part number is
the "AFN" portion. The "AN" or "A" was a buggy chip; the "AFN" is the current
bug free version with the F being significant. The "N" suffix is just an
indicator of the chip packaging. The Western Digital 16C550, although similar
in appearance and supposed purpose, has proven to be inadequate. Mixed reports
have been heard about the Goldstar 16550 and the 16550 VLSI chip used on some
motherboards where the serial port is integrated on the motherboard itself.

You might want ask, when purchasing an internal modem, whether the UART
capabilities of that modem are enabled with a VLSI (Very Large Scale
Integrated circuit) chip that emulates the 16450 or a 16550AFN. Some internal
modems use the actual NS16550AFN chip itself. This might be an important
consideration if you plan on using the modem in a multitasking environment
where the 16550AFN becomes crucial. Swapping these components on an internal
modem is difficult at best; impossible in other cases.

There is a difference - between these two words, COMPLIANT is the more
desirable. Compatible means it will recognize and in many instances, function
like the method or function it is compatible with. However, it does not
guarantee that it achieves this compatibility by the same method the standard
that dictates the method calls for. If a program or feature is dependant on
compliance with a standard, it is possible that a compatible modem will work
with that application or feature. Some other program or feature might rely on
complete compliance with the standard and not recognize the method the
compatible modem uses to achieve compatibility. If a feature or method you
use is a requirement, it is best to demand the modem be not only compatible,
but compliant in the method it uses in achieving that feature.

Synopsis of Modems and Compatibility:
These modems will usually be downwardly compatible with 2400 bps modems. Some
modems will not negotiate a 300 bps CONNECT. Most, at a minimum, will be
compatible with 1200 and 2400 bps standards. There have been reports of some
modems having problems with some 2400 bps modems - this is usually the fault
of the 2400 bps modem not being fully COMPLIANT with the standards. Because of
the stricter guidelines imposed by 9600, the likelihood of a 9600 modem
manufacturer cutting corners is less likely than the 2400 manufacturer. Most
9600's have an auto-fallback mode that will detect the highest negotiable bps
rate, either through hardware or software configuration. As stated
previously, if the modem is v.42 capable, it will fall back to MNP if
the other modem is not v.42 capable, but is MNP capable. Modems supporting
MNP will connect with data compression/error correction with other MNP
modems at the highest bps rate negotiable.

Listed in alphabetical order by brand name -

CompuCom Champ
The Champ uses a proprietary CompuCom Speed Protocol (CSP) to communicate
at 9600 bps.
- CONNECTs to other CSP modems at 9600 bps.

CompuCom Storm
The Storm uses a proprietary CompuCom Speed Protocol (CSP) to communicate
at 9600 bps and the CCITT v.32 method for communicating at 9600 bps.
- CONNECTs to other CSP modems at 9600 bps.
CONNECTs to v.32 modems at 9600 bps.
CONNECTs to v.32bis modems at 9600 bps.
CONNECTs to v.32 dual mode modems at 9600 bps.
CONNECTs to v.32bis dual mode modems at 9600 bps.

CompuCom Challenger
The Challenger uses a proprietary CompuCom Speed Protocol (CSP) to
communicate at 9600 bps and the CCITT v.32bis method for communicating at
14,400 bps.
- CONNECTs to other CSP modems at 9600 bps.
CONNECTs to v.32 modems at 9600 bps.
CONNECTs to v.32bis modems at 14,400 bps.
CONNECTs to v.32 dual mode modems at 9600 bps.
CONNECTs to v.32bis dual mode modems at 14,400 bps.

Generic V.32:
Uses the CCITT method of communicating at 9600 bps.
- CONNECTs to v.32 modems at 9600 bps.
CONNECTs to v.32bis modems at 9600 bps.
CONNECTs to v.32 dual mode modems at 9600 bps.
CONNECTs to v.32bis dual mode modems at 9600 bps.

Generic V.32bis:
Uses the CCITT method of communicating at 14,400 bps.
- CONNECTs to v.32 modems at 9600 bps.
CONNECTs to v.32bis modems at 14,400 bps.
CONNECTs to v.32 dual mode modems at 9600 bps.
CONNECTs to v.32bis dual mode modems at 14,400 bps.

Hayes V-Series:
The Hayes V-Series uses a proprietary method of communicating at 9600 bps.
- CONNECTs to other Hayes V-Series modems at 9600 bps.
CONNECTs to other Hayes ULTRA modems at 9600 bps.

Hayes ULTRA:

The Hayes V-Series uses a proprietary method of communicating at 9600 bps
and CCITT v.32 for communicating at 9600 bps.
- CONNECTs to Hayes V-series modems at 9600 bps.
CONNECTs to v.32 modems at 9600 bps
CONNECTs to v.32 dual mode modems at 9600 bps.
CONNECTs to v.32bis dual mode modems at 9600 bps.

Hayes ULTRA 14,400:
The Hayes V-Series uses a proprietary method of communicating at 9600 bps
and CCITT v.32bis for communicating at 14,400 bps.
- CONNECTs to Hayes V-series modems at 9600 bps.
CONNECTs to v.32 modems at 9600 bps
CONNECTs to v.32bis modems at 14,400 bps.
CONNECTs to v.32 dual mode modems at 9600 bps.
CONNECTs to v.32bis dual mode modems at 14,400 bps.

Telebit Trailblazer:
Uses proprietary PEP method of communicating at 9600 bps.
- CONNECTs to other Telebit Trailblazers at 9600.

Telebit T-2500:
Uses proprietary PEP method of communicating at 9600 bps and CCITT v.32 for
9600 bps.
- CONNECTs to Telebit Trailblazers at 9600.

CONNECTs to v.32 modems at 9600 bps.
CONNECTs to v.32bis modems at 9,600 bps.
CONNECTs to v.32 dual mode modems at 9600 bps.
CONNECTs to v.32bis dual mode modems at 9600 bps.

USR Courier HST 9600:
Uses the USR proprietary HST method of communicating at 9600 bps.
- CONNECTs to HST 9600 bps modems at 9600 bps.
CONNECTs to HST 14.4 bps modems at 9,600 bps
CONNECTs to HST v.32/DS's at 9600 bps
CONNECTs to HST v.32bis/DS's at 9600 bps

USR Courier HST 14.4:
Uses the USR proprietary HST method of communicating at 14,400 bps.
- CONNECTs to HST 9600 bps modems at 9600 bps
CONNECTs to HST 14.4 bps modems at 14,400 bps
CONNECTs to HST DS modems at 14,400 bps

USR Courier v.32/HST DS:
The v.32/Dual Standard uses the proprietary HST method for communicating at
14,400 bps and the CCITT V.32 method of communicating at 9600 bps.
- CONNECTs to 9600 HST's at 9600 bps.
CONNECTs to v.32 modems at 9600 bps.
CONNECTs to v.32bis modems at 9,600 bps.
CONNECTs to 14.4 HST's at 14,400 bps
CONNECTs to v.32 dual mode modems at 9600 bps.
CONNECTs to v.32bis dual mode modems at 9600 bps.
CONNECTs to USR v.32/Dual Standards at 9600 bps with v.32
CONNECTs to USR v.32/Dual Standards at 14,400 bps with HST
CONNECTs to USR v.32bis/Dual Standards at 9600 bps with v.32bis
CONNECTs to USR v.32bis/Dual Standards at 14,400 bps with HST

USR Courier v.32bis/HST DS:
This Dual Standard incorporates both the proprietary HST method and the
CCITT V.32bis method of communicating at 14,400 bps.
- CONNECTs to 9600 HST's at 9600 bps.
CONNECTs to v.32 modems at 9600 bps.
CONNECTs to v.32bis modems at 14,400 bps.
CONNECTs to 14.4 HST's at 14,400 bps
CONNECTs to v.32 dual mode modems at 9600 bps.
CONNECTs to v.32bis dual mode modems at 14,400 bps.
CONNECTs to USR v.32/Dual Standards at 9600 bps with v.32
CONNECTs to USR v.32/Dual Standards at 14,400 bps with HST
CONNECTs to USR v.32bis/Dual Standards at 14,400 bps with v.32bis
CONNECTs to USR v.32bis/Dual Standards at 14,400 bps with HST

Whatever choice you make, I hope this file was of some help in deciding
which modem you buy.

MODEM 101: An Introductory Lesson in High-Speed Modems
by Nancy Hattaway
Sempervirens BBS, Concord, CA

Jim, an avid bulletin board caller, wanted to upgrade from his 2400
baud modem to a high-speed modem. He went to his computer dealer and
asked for the best 9600 baud modem, and purchased a Hayes V-series
Ultra Smartmodem 96, which is indeed one of the best on the market.
Jim felt that getting the best justified spending $800 on the modem.
However, when Jim got his new modem home and set it up, he found that
all of his connections were still at 2400 baud. Many of the sysops
who ran the bulletin boards Jim called were as confused as he, but one
of them targeted the problem. While Jim's modem was an excellent V.32
modem, the bulletin boards were using HST modems. Jim wasn't quite
sure what this meant, but returned to his computer dealer and
explained the problem. His vendor made him a fair compromise offer:
for returning the Hayes and $100, he sold Jim a U.S. Robotics Dual
Standard, which, although more expensive than the Hayes Ultra, can
connect to both V.32 and HST modems at high speed. Jim was very happy
with his new modem. However, he was not so happy when he saw a V.42bis
modem priced at $179, much less than he had paid for his V.32. Jim
called the sysop who had understood his first problem and was told
that this time he had no problem, because a V.42bis modem with no
other designation was a 2400 baud modem, no faster than Jim's older
2400 baud.

Although the name was changed, Jim's story is true, and illustrates
one of the most common areas of confusion in today's telecommunication
field. Jim faced several sources of confusion. The designations
V.32, V.42bis and HST indicate the modem's abilities, but do not
describe them to the uninitiated. Jim was also using the word "baud"
imprecisely without knowing it. If a modem buyer doesn't understand
the jargon of modem descriptions, it is easy to spend a large amount
of money and purchase a modem that doesn't function with any more
efficiency than a $79 modem from a warehouse store.

What makes two modems compatible?

Modems speak to other modems. In order to do so, the two modems in
question must speak the same "language", otherwise they cannot
communicate. In the early days of modems, the "language" used by the
Hayes Microcomputer Products company was taken as a standard by most
modem manufacturers. For medium speed modems (1200 and 2400 bits per
second, or bps), this is still the case. Most of these modems use the
Hayes "AT" command set and speak freely to one another.

When manufacturers first began making high speed modems (9600 bps and
above), no clear standard evolved. Several manufacturers developed
proprietary protocols such as HST and PEP (see below). Proprietary
protocols are owned by the company which developed them, and thus none
of these modems could communicate with any of the other types at 9600
bps, because none of them spoke the same "language."

The United Nations, through the Comit‚ Consultatif International de
Telegraphie et Telephonie (known as the CCITT), is charged with
establishing a recognized standard for high speed telecommunication.
The CCITT, based in Geneva, has defined many telecommunication
standards, some relating to modems, others to fascimile transmission,
and still others to packet-switching and other telecommunications.
All of the CCITT standards pertinent to modems are recognizable by
their "V.nn" designation. One thing to keep in mind as you are
reading is that the "V-dot" protocols such as V.32, V.42, and V.42bis
are totally different standards, although they are commonly confused.
The -bis suffix also causes confusion. It is easiest to think of -bis
as meaning "another protocol". We'll describe each CCITT standard in
turn, then summarize the differences.

Before beginning, you should know that "baud" does not technically
refer to the speed of a modem, but to an aspect of how the
transmission occurs (more precisely, the number of changes of state in
the communication line per second). The smallest unit of binary data
(0 or 1) is called a "bit", short for BInary digiT. A 300 baud modem
utilizing a method known as frequency shift keying sends one bit per
baud and is therefore also a 300 bps modem. A 1200 bps modem is
usually a 300 baud modem using a different method in order to transmit
four bits per baud. Confused? Just forget you ever heard the word
"baud" and use the initials "bps".

Another term used in modem descriptions is "duplex". This term, when
used in reference to a modem, indicates whether or not data is
transmitted out and received in simultaneously at the designated
speed. Modems using full duplex protocols can transfer data both
directions simultaneously at their rated speed. Half duplex protocols
allow data to be sent in only one direction at a time. A signal on
the end of the information tells the receiving modem that it is now
free to transmit. "Asymmetrical" duplex indicates that information
flows in both directions simultaneously, but at different speeds.
"Adaptive" duplex means that the modems may transmit anything from
full to half duplex, depending on the situation.

CCITT protocols: data transmission or "speed"

V.22: You may rarely see a reference to the V.22 protocol. Modems
using V.22 are almost universally called "1200 baud" modems rather
than V.22 modems. This is a 1200 bps data transmission protocol. A
data transmission protocol specifies the "modulation technique", or
method used to transfer the data. It therefore dictates the fastest
speed at which information can be transferred. Thus, data
transmission protocols are often called "speed" protocols. In
addition to the rate of the character stream, data transmission
protocols define such things as methods used to limit the effect of
telephone line noise, so they are not technically just "speed"

V.22bis: V.22bis is the data transmission protocol recommended by the
CCITT for 2400 bps modems. The modulation technique used by V.22bis
modems transmits four bits per baud, and these modems typically
are 600 baud modems. Four bits per baud at 600 baud is the same
as 2400 bps. These modems are usually called 2400 baud modems,
which is technically incorrect. From the consumer's standpoint, it
doesn't matter if your modem is a 600 baud modem transmitting four
bits per baud, or a 2400 baud modem transmitting one bit per baud.
Both have a "speed" of 2400 bps. V.22bis is a full duplex protocol.

V.32: V.32 is also a data transmission protocol. It is a 4800 bps and
9600 bps standard employing a method called trellis coded quadrature
amplitude modulation (TCQAM) at 2400 baud. TCQAM encodes 2 or 4 bits per
baud and is a full duplex protocol. Until the advent of V.32bis, V.32
was considered to be the standard for high-speed modems. However, it
was introduced only after certain proprietary transmission protocols
had become well established, and thus has shared, but not dominated
the high speed data transmission market.

V.32bis: V.32bis is the newest data transmission protocol from the
CCITT, with final approval of the standard expected in spring or
summer of 1991. V.32bis is a 14400 bps full duplex protocol, encoding
6 bits per baud at 2400 baud. There are already several modems being
marketed which adhere to the proposed V.32bis standard. It is
considered unlikely that major changes will occur prior to final
approval that would cause these "pre-approval" V.32bis modems to be

Thus, the "V-dot" protocols that determine data transmission or
"speed" are, in order from slowest to fastest, V.22 (1200 bps),
V.22bis (2400 bps), V.32 (4800 bps or 9600 bps), and V.32bis (14400
bps). All are full duplex protocols. The remaining "V-dot" protocols
do not determine "speed", but are concerned with error correction
(ensuring that the data received is an exact copy of the data sent)
and data compression (coding the data into a smaller form so that it
takes less time to send at the rated speed).

CCITT protocols: error correction and data compression

V.42: V.42 is an error correction protocol. V.42 uses a method known
as link access protocol for modems, or LAP-M. It helps to ensure that
transmission of data is done without error. Unlike the protocols
discussed above, V.42 does not relate to the speed of data
transmission, only to its correctness. However, V.42 can decrease the
actual time for transmission at a given transmission speed.

This requires a little more explanation. One way of measuring the
speed of data transmission is by characters per second, or cps. Each
character consists of 10 bits, thus a 2400 bps modem has a theoretical
character rate of 240 cps (the number of bits per second divided by
the number of bits in a character). In reality, this figure is closer
to 235 cps, because no transmission is totally efficient. This rate is
commonly referred to as the "throughput" because it indicates how many
characters the modem can "put through" in a given time. The 10 bits
in each character include 8 bits of data plus a "start" bit and a
"stop" bit. The V.42 error correction protocol strips off the excess
start and stop bits and thus reduces the data load by 20%. The actual
throughput increase is less, due to protocol overhead, but is about
15% (270 cps at 2400 bps with excess bits stripped off compared to 235
cps at 2400 bps without).

V.42bis: V.42bis is a data compression standard. Data compression is
commonly used to reduce the size of a file for storage or
transmission. Smaller files naturally take less time to transmit.
V.42bis uses a method of compression called Limpel-Ziv encoding, which
typically can achieve a 4:1 compression ratio on an uncompressed
ASCII text file, meaning four times as much data can be sent in a
given time at a given transmission rate. With V.42bis compression, a
V.32 (9600 bps) modem can achieve an effective transfer rate of 19200

However, many files have been compressed before they are transmitted,
usually so that they can be stored in less space on a hard disk or
floppy disk. This process, commonly called "archiving", uses one of a
variety of proprietary or public domain compression techniques. DOS
files that have been compressed usually have extensions such as .ZIP,
.LZH, .ARC or .GIF which identify the compression technique used.
If a modem tries to further compress a file that has already been
compressed, it actually increases the time needed for transmission.
Therefore, the V.42bis standard includes the ability to "sense"
pre-compressed files and disable the V.42bis compression for such

V.42 and V.42bis are commonly confused with the other V-dot protocols.
Unlike V.22, V.22bis, V.32 and V.32bis, all of which define a data
transmission speed, V.42 and V.42bis have no effect on speed, but are,
respectively, error correction and data compression protocols. The
modem Jim saw advertised for $179 was a 2400 bps modem with V.42bis
data compression ability.

Proprietary data transmission protocols

The CCITT standards are, by definition, world-wide and non-proprietary.
However, other protocols exist that define data transmission, error
correction and data compression. Proprietary data transmission
protocols in use in modems being sold today include the HST, DIS and
PEP protocols. Proprietary error correction and data compression
protocols in use today include MNP level 6 and higher and CSP.

Proprietary high speed data transmission protocols are owned by the
companies which developed them and cannot be used by anyone else
without a license. The cardinal rule to remember about data
transmission protocols is that two modems with different high speed
protocols will not be able to communicate with each other at high
speed. However, since all these modems have a standard 2400 bps
protocol as a "fall-back" protocol, these modems will be able to
connect in most cases and communicate at 2400 bps.

HST: The HST (High Speed Transmission) modulation is similar to
V.32 in the fact it uses a trellis coded quadrature amplitude
modulation (TCQAM) technique. Unlike the V.32, it is not full
duplex, but instead sends data at a maximum of 14400 bps in one
direction with either a 300 or 450 bps frequency shift keyed reverse
channel. This makes it an "asymetrical duplex" modem. The main TCQAM
channel encodes up to 7 bits per baud, at 2400 baud, with one bit used
as parity, for the theoretical maximum of 14400 bps in one direction.
The modem will switch channels as the data demands. The HST protocol
is proprietary to U.S. Robotics (USR).

The meanings of the initials USR and HST are often confused. All HST
modems are made by USR, but USR makes other modems which do not use
the company's proprietary protocol. For instance, USR makes a modem
which uses only their proprietary HST protocol, the USR Courier HST.
However, they also make a high speed modem that conforms to the CCITT
standard only, the USR Courier V.32. A third, and very popular, modem
marketed by USR includes both the CCITT V.32 protocol and the proprietary
HST protocol. This modem, the USR HST Dual Standard HST V.32, will
connect at high speed to an HST only modem or to a modem that has V.32
only, thus the name Dual Standard. The logic for both protocols
actually exists side-by-side in the Dual Standard modems. Recently,
USR has begun producing modems that utilize the new V.32bis protocol,
both as a single protocol modem and as a Dual Standard modem.

DIS: The DIS protocol, like the V.32, V.32bis and HST protocols, uses
quadrature amplitude modulation to acheive a data transmission rate of
9600 bps. The major difference between DIS modems and others,
however, is the method used to control "noise", or unwanted signals on
the telephone line. A "noisy" telephone line can cause errors in data
transmission or even cause loss of carrier before the transmission is
finished. The CCITT standards call for use of echo cancellation to
filter out unwanted line noise. Echo cancellation requires a digital
signal processor, which greatly increases the cost of the modem. DIS
uses a method of improving the signal-to-noise ratio which does not
require the processor. Thus, modems using the DIS protocol are
significantly less expensive than V.32, V.32bis, or HST modems. DIS is
a proprietary product of CompuCom Corporation.

PEP: The PEP (Packetized Ensemble Protocol) modulation technique,
which is a proprietary product of the Telebit Corporation, is totally
dissimilar to the protocols described above. It uses a method called
dynamic adaptive quadrature amplitude modulation (DAQAM). Effectively,
it splits the phone line into 511 sections and puts a 34 baud carrier
on each section. By encoding up to 4 bits per baud, PEP achieves
maximum speeds of 18000 bps (uncompressed). Each channel can be going
only one direction, so full duplex operation can be had at 9000 bps.
PEP also utilizes adaptive duplex, which means that the speed over the
various channels will be determined by the data being sent. If data is

being sent in only one direction, it will transmit at 18000 bps in
that direction. However, if full duplex is needed, data will be sent
at 9000 bps in both directions. If traffic is heavier in one
direction than the other, the PEP protocol adjusts to ensure a maximum
data transmission rate. Modems using the PEP protocol are common in
systems using the UNIX operating system.

Other error correction and data compression protocols

The most common non-CCITT error correction and data compression
protocols are those developed by Microcom, Inc. These are all
indicated by the letters MNP (Microcom Network Protocol) and a number
which differentiates between the various MNP protocols. MNP levels
2-4 (error correction) and MNP level 5 (data compression) are in
widespread use and are found on most high speed modems, including
those that meet CCITT standards.

The reason for this is that both the V.42 standard and the V.42bis
standard include an annex which requires that MNP levels 2-4 (for
V.42) or MNP level 5 (for V.42bis) be available as "fall-back"
protocols. In the case of error correction, this ensures that if both
modems are not V.42 compliant, at least MNP level 4 error correction
will be used. MNP level 4 is similar to V.42 in that it strips the
start and stop bits from each 10-bit character, thus increasing
throughput by about 15%. The MNP level 4 protocol includes MNP levels
2 and 3, which are also error correction protocols.

Note that some 2400 bps modems do not have any error correction or
data compression ability. These are often referred to as "non-MNP" or
"non-error correcting" modems. When such modems are used for data
transmission, software (such as the Zmodem file transfer protocol) is
used to provide error correction. Modems which have at least MNP
level 4 error correction or V.42 error correction (which includes MNP
level 4 as a fall-back protocol) can instead use a file transfer
protocol such as Ymodem-G, which is faster because it sends the data
in a stream with no software-controlled error correction.

MNP level 5 is the most commonly seen non-CCITT data compression
protocol, and is included in the CCITT V.42bis standard as a fall-back
protocol. MNP level 5 differs from V.42bis in two important ways.
First, while V.42bis uses a 4:1 data compression protocol, MNP level 5
uses a method called run length encoding, which is only a 2:1 data
compression protocol. Microcom did develop a 4:1 compression protocol
(MNP level 9) but that did not provide much of a challenge to V.42bis.

The second difference between V.42bis and MNP level 5 is that, while
V.42bis can "sense" previously compressed files and disable V.42bis
compression, MNP level 5 does not have this capability. Attempting to
further compress an already compressed file slows transmission.
Therefore, if a modem with MNP level 5 (but not V.42bis) capabilities

is used mostly for previously compressed files, as is the case with
most bulletin board file transfers, MNP level 5 should be disabled on
that modem, usually by toggling a DIP switch or changing a software
setting. If the modem is used for uncompressed text file transfers,
MNP level 5 should remain enabled.

MNP level 5 is often erroneously referred to as an error correction
protocol. This is partially because modems tend to be referred to by
their most sophisticated feature. Thus, an "MNP 5 modem" is
considered better than an "MNP 4 modem". In fact, this is true,
because the MNP level 5 modems always include MNP levels 2-4.
However, it is imprecise to refer to a modem as an "MNP 5 error
correcting modem". In such a modem, only MNP levels 2-4 have anything
to do with error correction, while MNP level 5 is strictly a data
compression protocol. It is more precise to describe such a modem as
an "error correcting modem with MNP level 5 compression".

A non-CCITT, non-Microcom error correction and data compression
protocol called CSP (Compucom Speed Protocol) is used with modems
employing the DIS data transmission protocol. These same modems offer
MNP levels 2-5 as fall-back routines for times when the DIS modem
connects to a non-DIS modem (at 2400 bps, as DIS is a proprietary
protocol). CSP offers compression of up to 4:1 on noncompressed files
without apparent degradation of file transfers on precompressed files.
It is a proprietary technology of CompuCom Corporation.

Summing it up

Modem protocols can dictate the data transmission characteristics such
as speed and telephone line noise reduction. Examples of this type of
protocol include V.22, V.22bis, V.32, V.32bis, HST, DIS and PEP.

Modem protocols can also provide error correction, at the same time
increasing throughput by about 15%. Examples of this type of protocol
include V.42 and MNP levels 2-4.

Finally, modem protocols can compress data that has not been
previously compressed, which shortens transmission time by decreasing
file size. Examples of this type of protocol are V.42bis and MNP
level 5. The CSP protocol handles both error correction and data
compression for modems using the DIS data transfer protocol.

Trademark Information

"Dynamic Impedance Stabilization", "DIS", "CompuCom Speed Protocol",
and "CSP" are trademarks of CompuCom Corporation.

"Hayes V-series" is a registered trademark of Hayes Microcomputer
Products, Inc.
"ULTRA Smartmodem 9600", "Ultra" and "Smartmodem" are trademarks of
Hayes Microcomputer Products, Inc.

"Microcom Networking Protocol" and "MNP" are registered trademarks of
Microcom, Inc.

"MS-DOS" is a registered trademark of Microsoft Corporation.

"PEP" and "Packetized Ensemble Protocol" are trademarks of Telebit

"UNIX" is a registered trademark of American Telephone & Telegraph.

"USRobotics" is a registered trademark of U.S. Robotics, Inc.
"Courier", "HST", and "Dual Standard" are trademarks of U.S. Robotics,

  3 Responses to “Category : Various Text files
Archive   : GFILES.ZIP
Filename : 9600-INF.TXT

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  3. But one thing that puzzles me is the “mtswslnkmcjklsdlsbdmMICROSOFT” string. There is an article about it here. It is definitely worth a read: