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 phone, 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 is 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 recognize 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 could 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 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 that 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 data 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 communicate 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 appearance 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" where "+++" stands for any escape character and "" 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 thinking 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 transferred 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 Ñ 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 protocols 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 transfer 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 software 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 manufacturers 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 possible 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 transmitting 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 communications 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. For example, in a scan of 5,684 megabytes of data on hard drives at Hayes headquarters, Dr. Copeland found one unintentional occurrence of the TIES escape sequence per every 34 megabytes of data. Calculations based upon the actual data checked by Dr. Copeland indicate that the occurrence of the TIES escape sequence may be far greater for actual data than for random data. Placing the calculations provided by the chip set manufacturer in terms of the "real world," in a company using 700 TIES modems communicating continuously at 9600 bps, there would be an inadvertent escape twice a week. Twice a week a data file important to the business would not be sent because it could not get through the TIES modem. Hayes believes that any inadvertent escape is unacceptable. Two inadvertent escapes each week is unacceptable. And if the data is being sent at 38.4 kbps, as many new modems are now capable of doing, this TIES block could occur more than once per day. The following chart using the figures provided by the TIES chip set manufacturer, represents the frequency of TIES blocks that you could expect with a TIES modem (if data were truly random) depending on the number of modems and the speed at which they are operating: If Data was Random Type of Use Hours per Day Modem No. of TIES Speed Modems Aborts per Year Single User 1 2400 1 0.001 Small BBS 12 9600 2 0.12 Large BBS 12 14400 12 1.1 Small Company 2 14400 50 0.8 Medium Company 2 14400 500 7.6 Large Company 2 14400 5000 76.0 Dialup WAN 24 14400 200 36.0 Dialup WAN 24 38400 200 97.0 In data which had one occurrence of the TIES escape sequence per 50 megabytes of data, a user could expect the following results*: Data with 1 TIES per 50 Mbytes Type of Use Hours per Day Modem No. of TIES Speed Modems Aborts per Year Single User 1 2400 1 6 Small BBS 12 9600 2 605 Large BBS 12 14400 12 5,449 Small Company 2 14400 50 3,784 Medium Company 2 14400 500 37,843 Large Company 2 14400 5000 378,432 Dialup WAN 24 14400 200 181,647 Dialup WAN 24 38400 200 484,393 (* Your data may differ.) 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 upgrades 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 characters 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 new 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 remainsÑwhat 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 Reliability? 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 Heatherington 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 or 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 more 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.