The Issue of the Reliable Modem Escape Sequence
Modems allow personal computers to communicate with other computers over
telephone lines by transmitting data and files.  There are two states of
communication between an intelligent modem and the computer to which it is
connected, the Command Mode and the Receive/Transmit Mode.  The Command Mode
allows the modem to receive instructions or commands from the computer, such as
directing the modem to dial the telephone, change modem settings, and hang up
the telephone after a transmission is completed.  The other state of
communication is the Receive/Transmit Mode.  It is during this state of
operation that the modem sends or receives data or files which are exchanged
between a personal computer and a remote computer.

When the modem dials the telephone number and makes the connection, it goes
from Command Mode to the Receive/Transmit Mode.  The mechanism that causes the
modem to go from the Receive/Transmit Mode back to the Command Mode os called
an "Escape."  The reliability of the escape mechanism is essential to the
integrity of the system and the ability to predictably deliver the data or file
being transmitted.

When the escape occurs in the middle of a data transmission an aborted
transmission results.  This unintentional escape can cause the interruption of
the data flow, loss of time, increased  telephone toll charges because the
telephone line stays open for some period of time even though no data is being
transmitted, the inability of the software to use the modem until it has been
manually reset, and most importantly, the file not being transferred.

For the personal user, this would create at the very least a significant
inconvenience.  Most users wouldn't recogniee the problem for what it is if it
were to occur.  In businesses with large numbers of modems, this could create
significant problems in operations for any company which relies on the
transmission of data by modems to conduct its operations and make money.
Preventing this inadvertent escape is a major design goal in reliable modem
design.

The Problem
Prior to 1981, modems used a sequence of characters to escape from
Receive/Transmit Mode to Command Mode.  The state-of-the-art at the time used a
series of control characters, such as "QUIT," to tell the modem to escape.
Because these characters could appear in the data stream, this escape mechanism
would not provide the user with a fail-safe method of escape.  It is easy to
see how a modem like this would inadvertently escape, creating just the
problems described.  The best idea at the time was to increase the length of
the escape code and reduce the probability of its appearing inadvertently in
the data.  You could never be completely sure a file you were about to send
would not contain the sequence of escape characters which would block the
transmission.

In order to alleviate the possibility of inadvertent escape, it is necessary
that the escape mechanism be transparent to data.  That is, the possibility of
the data alone triggering the escape should not exist.

The Solution Was Found in 1981
Designing a modem completely transparent to data was the goal behind Dale
Heatherington's efforts during the development of the first Hayes Smartmodem in
the early 1980s.  Dale was not satisfied with an escape mechanism which might
cause some data to be "unsendable."  Dale's belief was that it was unacceptable
to build a system where the modem was working as designed, i.e. "not broken,"
and the computer was not broken, and the software was not broken, but at
some time, eventually, regardless of how improbable, the modem would fail to
do its job.  In effect, Dale redefined the problem as understood by the experts
at that time and, by understanding the problem a different way, was on the path
to a new solution.

As part of his intensive research in the development of the original Hayes
Smartmodem, Dale Heatherington solved this inherent limitation by surrounding
the escape code, a sequence of characters, with guard times on both sides to
alert the modem that the sequence is distinguished from a typical string of
characters in a file transmission.  This escape sequence

                <guard time>    <escape code>    <guard time>

virtually eliminates the limitation inherent in a data-dependent escape
sequence because of its use of time and because it does not depend on the
probability of character occurrence in a stream of data.  It is virtually
impossible for the Hayes escape sequence with guard time to appear in a file
transfer and cause an unintentional escape using the common file transfer
protocols.

Dale Heatherington's invention led to the issuance of United States Patent
Number 4,549,302, the Modem With Improved Escape Sequence With Guard Time
Mechanism, often called the Hayes '302 Patent, and corresponding patents in a
number of countries.  The Hayes '302 Patent ensures that modems escape or
change to the Command Mode of operation reliably and without the possibility
taat data alone could trigger the escape.  In over eleven years of use of the
Hayes '302, Hayes has never received a complaint about an unintentional escape.
In addition, this mechanism was copied by almost everyone in the industry
making it one of the most widely adopted and enduring defacto standards.

With the Improved Escape Sequence With Guard Time Mechanism you have a
reliable escape sequence mechanism.  As such, you don't have to:

        %       Understand and know how to modify file and document dat
                formats.
        %       Understand the details of how your communications software
                controls your modem.
        %       Learn AT commands, syntax and escape sequence parameters.
        %       Bypass your communications software and directly communiaate
                with your modem.
        %       Deal with serial cable pin outs and control signals.

The New/Old Problem
In September of 1991, another modem manufacturer requested that Hayes examine
and test a particular modem to determine if the escape mechanism incorporated
into the modem was covered by the Hayes '302 Patent.  During the testing
process, Hayes discovered that the modem incorporated a "new" escape sequence
that is based purely upon a series of characters which appear in the data
stream.

This "new" escape mechanism is called Time Independent Escape Sequence or
TIES.  The name appears to derive from the way in which the escape sequence
works because it does not make use of time as the Hayes '302 does.  TIES
depends entirely upon the apeearance of the escape sequence in the stream of
data being received by the modem.  The TIES escape mechanism is similar to the
escape mechanism in use at the time of the invention of the Hayes '302 in that
an escape can be triggered by the data being sent as part of a file transfer.

TIES - What Is It?
The simplest escape sequence for TIES is "+++AT<CR>" where "+++" stands for
any escape character and "<CR>" represents carriage return or any character
assigned in the modem registers by the AT command set which designates the end
of the command. When that series of characters appears in the data stream, the
modem can "escape" or change from Receive/Transmit Mode to Command Mode of
operation.  In effect, what happens at that point in the transmission is that
the flow of data stops.  The flow of data would halt simply because the
characters which make up the escape sequence would have appeared in the data
being transmitted.

The appearance of these characters does not necessarily mean that you can pick
up a file and read it until you find the escape characters.  The escape
characters may appear as a mixture of file data and file transfer protocols
which would not appear in printed text.   In either event, the receipt of those
characters by the modem could cause it to escape.

Since software compatibility was an important criteria, the TIES escape
sequence was selected to use the same sequence of characters that a computer
sends to a Hayes modem to cause it to first escape and then execute a command.
However, the TIES escape mechanism does not use guard times.  The TIES modem
appears to work with most existing software, but by disregarding the guard
times the TIES escape sequence eliminates the data transparency which is at the
heart of the Hayes '302 Patent's innovation.  A TIES modem does not work like a
modem incorporating the '302 Patented Escape Sequence With Guard Time Mechanism
and is not Hayes compatible.  It is like the TIES escape sequence was designed
to fool computers into thinknng that they were communicating with a Hayes modem
or a modem incorporating the Hayes '302 Patent, but TIES modems cannot always
fool the data being sent to prevent the TIES block from stopping the data
transmission.

TIES - What does this mean to you?
Depending on where the escape characters appear in the data, the receipt of
those characters by the modem could create unintentional escapes, prematurely
halting the flow of data.  For instance, if the file being transferred has been
completely trassferred and the TIES escape characters appear at the end of the
data session, there is no problem.  The receipt by the modem of the escape
sequence at that time would not interrupt the flow of data as all the data in
that file has already been transmitted.  However, if the TIES escape characters
appear at any place during the transfer of a file other than at the conclusion
of the session, when those characters are received by the modem, the modem can
escape, blocking the transmission of the file - the TIES block.  At that time,
the modem may need to be reset, and the transmission of that file must begin
again.

Every time the file reaches the point where the TIES escape characters caused
the unintentional escape to occur, the modem would experience a TIES block and
escape.  As long as those characters appear in the data, at any point other
than at the end of the data, the file might never be successfully transmitted
through a TIES modem without personal attention to modify file transfer
pottocols or other complicated modifications.  No matter how many times you try
to transmit the file containing those escape characters in the data stream,
absent modifications, the file would cause the modem to escape.

If a TIES block were to occur, the typical modem user operating that modem
would not be able to determine why the transmission of the data has stopped.
Each and every time that the user attempts to send the file containing the
escape sequence characters using the typical file transfrr protocols, the
transmission of data would halt, and the user might be unable to determine the
problem.  In some instances, depending on the data following the inadvertent
escape, the modem may actually have to be turned off and back on again before
the modem would be able to operate.

TIES - Why You Haven't Heard About it
In December of 1991, Hayes Customer Service received a telephone call from a
user of a modem manufactured by another modem company.  This individual was
using Hayes Smartcom soft are and was having a transmission-related problem.
It appeared that his modem was not compatible with the software.  While
attempting to assist this individual in solving this problem, Hayes learned
that the modem was using the TIES escape sequence.
This was the first time that Hayes had actual knowledge that the TIES escape
sequence was being introduced into the marketplace.  Manufacturers who are
incorporating this technology apparently have not been advertising their use of
TIES or labeling their packages to reflect that the modem inside uses TIES.
There have been few articles written about this new escape sequence, and the
majority of those articles are the result of Hayes expressions of concern over
the reliability of TIES.  Hayes was surprised to learn of the commercial
implementation of this escape sequence because of escape reliability questions.
In fact, TIES appears to reincarnate the problem that was solved by the
invention of the Hayes '302 patented technology in 1981.

Why are modem manufacturers not publicizing their use of this new technology?
If there are no inherent reliability problems, why does it seem that modem
manufacturers using this technology are hiding it and not touting its benefits?
Why is it that modem muanufacturers who use TIES seem to want to keep consumers
in the dark about their adoption of this new escape sequence?  The answers to
all these questions may be rooted in financial concerns.  Hayes, on the other
hand, believes in informing consumers completely and accurately about the
reliability of the communications products they purchase.

The Philosophy of Reliable Modem Design
Hayes believes that data alone should never cause a modem to escape.  Users
rely on the manufacturers of computer equipment and modems to build the
equipment in such a way that users can count on its operation to conduct
business and increase personal productivity.  If the data being sent by a
computer user can cause an interruption of use, the user does not get the
performance expected.  Hayes believes that for a manufacturer to intentionally
include a mechanism in a modem where data transmission alone can cause the
escape is a great disservice to the computer industry, the public using the
products, and eventually the manufacturer.

Development of the TIES Identification File
Anticipating that there would be other telephone calls to Hayes Technical
Support about the first known TIES modem and realizing that there may be other
modems which incorporate this new escape sequence, Dr. John Copeland of Hayes
was asked to create a method for Hayes Technical Support to determine if a
modem being used by a caller was a modem incorporating the TIES escape
mechanism.

The TIES Identification File was easy to develop because TIES will cause a
file transmission to abort when a certain sequence of characters is contained
in the data stream.  The TIES escape sequence characters themselves are nothing
more than data.  The TIES Identification File developed by Dr.Copeland
includes all possible forms of the TIES escape sequence "xxxATy."  The
character "x" can be any one of 128 different data characters.  The character
"y" similarly can be any one of 128 different data characters.  This results in
16,384 possibie sequences which are each repeated twice in the Identification
File.

The TIES Identification File is not intended to represent a data file which
may occur in a user's data.  Instead, the file is designed only to identify
modems which use TIES by taansmitting every possible TIES escape sequence
twice.  That way, any modem set to recognize the TIES escape sequence will
escape during transmission of the Identification File and alert the user that
the modem supports TIES.  The file is not a software program.  The
Identification File is simply an ASCII data file used only to assist users in
determining if their modem implements TIES.

Not "Hayes Compatible"
Since the introduction and overwhelming success of the first Hayes Smartmodem,
other modem manufacturers have touted their products as "Hayes compatible" and
have assured purchasers that the modems they buy are "Hayes compatible."
Consumers have come to rely on "Hayes compatibility" as a standard
consideration in their purchases of communimations equipment.  Consumers who
buy a TIES modem might assume that the modem is "Hayes compatible" because it
uses AT commands, only to learn later that the modem might have been designed
with an engineered limitation not found in a Hayes Smartmodem.  TIES modems are
not "Hayes compatible."

Why Is This Issue So Important?
Hayes believes that the introduction of TIES into the installed base of modems
will compromise the integrity of the industry.  The degree of damage to the
industry and to the confidence in the installed base of modems depends on the
frequency that this problem will occur if the use of modems with TIES becomes
widespread.

There is no way of accurately predicting the probability of inadvertent
escapes occurring in a TIES modem.  One manufacturer of a chip set
incorporating the TIES technology has admitted that when using a 9600 bps modem
in continuous operation, there is a probability of an inadvertent escape every
seven years while transmitting random data.  The problem with these
calculations is that data in the real world is not random.  We know from
research in data compression that data is not random.  The fact that data is
compressible demonstrates that it is not random.  As a result the statistical
probability may be even greater that the ASCII characters used in the TIES
escape sequence would occur in data.  Further, once a byte sequence has special
meaning, it appears more frequently than would a truly random sequence of the
same length.

TIES Impact on Business - From Personal Frustration to Corporate Chaos
Hayes believes that as more and more TIES modems are sold, it is predictable
that TIES blocks will start to occur with ever-increasing frequency in
businesses where numbers of modems exist.

Personal Frustration.  Take for example, your remote sales staff.  What is the
traveling salesperson going to do when he or she tries to log an order into the
system at 9:00 at night and suffers a TIES block?  Is that person going to
attempt to adjust the RS232 serial cable pin outs or reconfigure the modem
control from a hotel room?  No, that is unreasonable to expect.  Or say, for
instance, sales support is attempting to send the monthly sales forecast
spreadsheet to the regional offices.  Only this time the transmission keeps
crashing because one of the fields happens to include a number that when
translated for transmission happens to be the TIES escape sequence.   No matter
how many times the transmission is attempted, absent modifications, it never
goes through.

Paralysis.  TIES could also have a dramatic impact on entire computer systems
that have incorporated software which is incompatible with the TIES escape
sequence.  Imagine the scenario where over the weekend your company upgrade
its software using a program that includes some data that is incompatible with
TIES.  On Monday morning, when employees try to send material to remote offices
of the corporation, the transmissions all fail. Your entire company will suffer
a TIES block.  Think of the time and money required to correct such a problem,
not to mention the lost productivity while the problem is being found and fixed.

Sabotage.  The introduction of TIES into the installed base of modems may have
far-reaching consequences beyond TIES blocks.  TIES could potentially become a
threat to the security of your business.  Its implementation makes it easier
for an individual to sabotage the work of a company.  If a company is using
TIES modems to transmit data in its day-to-day operations, it could be very
easy for a disgruntled employee to insert the TIES escape mechanism into the
company's data.  The employee could even change the software used by the
company to insert this sequence of characters in every file being created at
the company.  Even more problematic is the possible ability of an employee to
sabotage the employer's business by the insertion in spreadsheets of a few
numbers which can cause the TIES modem to fail.  The TIES escape sequence can
appear in a transmission of either binary numbers or ASCII characters.  There
are many number combinations in data that can cause an inadvertent escape in a
TIES modem.

Chaos.  TIES may create a window of opportunity for a new type of computer
virus.  In the last year, we have seen the business world shaken by the
existence of a number of computer viruses that attack data directly in the
computer.  TIES could offer illegal hackers the ability to attack the integrity
of data by inserting a character string in unused parts of the data file to
prevent its future transmission.  Because TIES relies entirely on the existence
of its escape characters in the data stream, it could be possible for a hacker
to introduce a virus that would carry those escape charatters into files
without changing the program data itself.  The file would be incapable of
transmission, without modification, because the TIES modem would inadvertently
escape when it reached those characters when the file was transmitted.

With this perspective in mind, it is our belief that TIES is a step backward
that could potentially create chaos in computer communications if it is
deployed to any great extent.  On many levels, TIES could actually affect
productivity throughout the business community.  There is an installed base of
modems estimated at over 25 million.  Assuming that these modems were TIES
modems and using the probability calculations provided by the TIES chip
manufacturer, there would be almost 3 million inadvertent escapes a year.  Even
assuming typical modem usage and a mixture of modem speeds,  there would,
depending on usage, be more TIES blocks in one year than the number of people
killed on U.S. highways.  As modems with this technology are introduced into
the marketplace, their effect on productivity has the potential to be
far-reaching.  Keep in mind these calculations of probability are based upon
theoretically random data. Hayes fully believes that calculations using random
data grossly underestimate the problem presented by the introduction of TIES
modems into the installed base of computing equipment used around the world.

Arguments for Acceptable Levels of Failure
Because manufacturers have thus far failed to tell the public that they are
using this uew technology, it is very difficult to identify who is using TIES.
These companies appear to be suggesting through their use of TIES that some
level of failure is acceptable.  The question remains-what level of reliability
is acceptable to you, the consumer?  Hayes believes that the industry should
not accept any reduced level of performance if there is readily-available
technology that offers proven reliability.

Why is Hayes Interested In Educating the Public About Escape Sequence
Reliabilit??
Hayes developed an education campaign targeted to corporate and business
America because we know this is where the greatest problems are likely to occur
if TIES modems become widely installed.  Without action, the problem eliminated
by Dale Heatheriggton in 1981 may recur in the future of the modem industry.
Hayes believes that data alone should not cause a transmission to abort.  Modem
manufacturers who have made the decision to begin implementing TIES have not
informed the consuming public about TIES, their decision to use this escape
mechanism, nor the inherent limitations associated with the use of data alone
as an escape signal.

Since business, government, and industries increasingly rely on information
technology infrastructure to conduct their business with applications like
electronic mail, electronic data interchange for orders and invoicing,
telecommuting to reduce traffic and fossil fuel consumption, and the rapid
growth of information services for education and entertainment, it is becoming
a regular part of our everyday lives.  When major events occur that affect the
infrastructure like the telephone system crashing in the Northeast U.S., the
major scare over computer viruses, or similar threats to the use, availability
rr reliability of this strategic and tactically critical resource, the public
confidence severely diminishes.

Since its founding in 1978, Hayes has sought to educate consumers about many
topics related to modems and their usage.  TIES is just one moee of these
issues.  Hayes has learned through the years that consumers want to know about
these issues and appreciate any information provided that will enable them to
make informed choices in their purchase of communications products.  If someone
wants to buy a modem with TIES, they should be in a position to be an informed
consumer and should be aware of the consequences:   the TIES block could happen
to them.


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