The Time Independent Escape Sequence, or TIES, is a modem protocol standard invented to avoid a patent held by Hayes Microcomputer Products. TIES is an escape sequence that switches the modem from "data mode" to "command mode", allowing instructions to be sent to the modem to control it while still connected to the remote modem.
Smartmodem When inventing the first Smartmodem, Dale Heatherington was faced with the problem of distinguishing commands from data given that there were only two serial pins available for use in the RS-232C port. He eventually settled on having two modes of operation, switching between them with an escape sequence, +++. Of course, files being sent over the modem could contain the string +++. For instance, this page includes the sequence several times. If the modem simply looked for the string to arrive in the data stream also carrying this text, it would switch to command mode at inappropriate times and stop data transfer with the remote modem. There needed to be some way to distinguish a deliberate command from random data. Heatherington's solution to this problem was to introduce a delay on either side of the escape sequence, meaning that only a <pause> +++ <pause> would trigger the switch. A file containing the string being sent would not contain the pauses, so the modem would treat it as data to be sent, and stay in data mode. A user typing in the string deliberately would naturally pause after sending it to wait for the modem's response, inserting the pause without even being aware of it.
Bizcomp patent Hayes had initially filed for a patent on the electronic design of the Smartmodem in June 1981. Unknown to them at the time, in March 1980 Michael Eaton had filed a patent which included an escape sequence similar to the one introduced by Heatherington. Eaton's company, Business Computers Corp., or Bizcomp for short, introduced modems using this system in 1980, before the Smartmodem. When the patent, 4,387,440, was granted on 7 June 1983, Bizcomp immediately started sending out license demands to any company using a similar technique, including Hayes. They charged between $500,000 and $2 million up-front, and an additional 3% per-device, sliding down to zero if the company paid the entire $2 million. In September 1983, Hayes purchased a license from BizComp for $2 million, which included both a circuit design as well as a description of an escape sequence to trigger it. Although the concept was generally similar to their own, the Bizcomp patent differed in two key ways; one was that the escape sequence was not pre-defined and was set by the user during the startup, and the other was that it lacked the delay that was key to the way Hetherington's design worked. Among the many other companies approached by Bizcomp was USRobotics (USR). In 1984, USR sued Bizcomp in an effort to break the patent on the basis of obviousness and prior-art, and violation of the Sherman Antitrust Act in their efforts to monopolize the modem market.
Hayes '302 Hayes then updated their original patent application and re-filed it that October, this time including a lengthy abstract that focused entirely on the guard time and escape sequence, something that was mentioned only in passing in the original filing. They received patent #4,549,302 in October 1985, Modem With Improved Escape Sequence With Guard Time Mechanism, commonly known as the "Hayes '302" or the "Heatherington '302". It was this version that contained the description of the guard time. In October 1986, Hayes began sending notices for license fees of 2% per modem to any vendor using the guard time concept. This included any modem already manufactured, and Hayes sent bills for millions of dollars to a number of major manufacturers. Lawsuits immediately started flying. Within a month, USR petitioned the courts to add Hayes to their ongoing lawsuit against Bizcomp, claiming that the only licensee for the Bizcomp patent was Hayes, and that they only did so to "bankroll Bizcomp's efforts to enforce the patent". This, according to USR, made them co-conspirators in their monopolization efforts. USR's lawsuit was then joined by Prometheus Products, who Bizcomp had also previously sued, joining the cases. This was quickly responded to by Hayes, suing both for infringement. Microcom, Multi-Tech, and Ven-Tel then sued Hayes, and Hayes, in turn, sued Everex and Omnitel for patent infringement. Microcom and US Robotics settled out of court and agreed to license the patent, with USR paying both the royalty and Hayes' legal costs. Everex, Ven-Tel, and Omnitel stuck it out in court where the Hayes patent was upheld.
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