Протокол TIES: История обхода патентных ограничений в модемах

Modem protocol standard
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.

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.

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.

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, 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. Hayes had also licensed the '302 patent to two chipset manufacturers, Rockwell and Silicon Integrated Systems (SiS). In 1991 Rockwell introduced a new low cost chipset supporting the new v.32bis 14,400 bit/s standard, one of the first to do so. It was an immediate bestseller, and other chipset companies immediately scrambled to catch up, all of them licensing '302 as well. Some even offered versions with both TIES and Hayes escape sequences, which could be determined via AT commands that returned the internal configuration of the modem, typically ATI4. TIES was seen mostly in "off brand" 1200 and 2400 bit/s modems, which were never a large market compared to the high speed models that followed, it quickly disappeared in the early 1990s when almost all manufacturers switched to Rockwell chipsets, or one of its many clones. The one major exception was Telebit, who used TIES in all of their models released after 1991, namely the T1600, T2500 and WorldBlazer. It is particularly interesting that Telebit would not license the '302 patent, considering that they sold into an upscale market and generally cost over $1000. Apparently, for some time a number of Hayes employees would post to the Usenet with strings like "+++ATH" in the text. This would cause a TIES modem to hang up. It was also used on IRC to disconnect people using dial up Internet access by sending ICMP ECHO REQUEST containing the string +++ATH0 and thus the modem hanging up when the victims' computer sent back the ICMP payload in the reply. The Hayes patent #4,549,302 expired on October 11, 2003. TIES however is still used today in many modems especially ones by Conexant.