The Time Independent Escape Sequence, or TIES, is a modem protocol standard invented to avoid a patent held by Hayes Microcomputer Products.
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.
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.
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.
[2] 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.
[4] 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".
In October 1986, Hayes began sending notices for license fees of 2% per modem[5] to any vendor using the guard time concept.
Microcom and US Robotics settled out of court and agreed to license the patent,[6] with USR paying both the royalty and Hayes' legal costs.
This would occur, on average, about once per gigabyte, which was at that time an extremely large size – most hard drives of the era were about 40 MB.
Sierra Semiconductor, which manufactured modem chipsets that supported TIES, had already won two preliminary injunctions in Minnesota and California.
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.