patent review, claiming the concept had long been used in the industry. A flurry of suits and countersuits followed. The bid to overturn the patent failed in 1986. Some time later, Hayes received permission to bring suits in federal court against infringers, and filed an initial suit against several major manufacturers, Everex, Ven-Tel, Omnitel and Prometheus Products. Competitors derisively termed it the "modem tax", and a number of manufacturers banded together and introduced the Time Independent Escape Sequence, or TIES, but it was not as robust as Heatherington's system and never became very successful. Higher speeds and increased competition Hayes was not as fast as some other manufacturers to release modems that ran faster than 2400 bit/s, which opened the door for U.S. Robotics (USR) and Telebit to meet market demand with faster products. Telebit was the fastest, running up to ~18,500 bit/s and maintaining higher speeds on noisy lines where other models would fall-back to lower speeds. They were also expensive and found mostly in professional settings, notably for Unix-running minicomputers for UUCP use where their protocol spoofing offered further speed improvements. USR's designs were simpler than Telebits and ran at "only" 9,600 bit/s, but carved out a strong niche by offering deep discounts to sysops. In 1987 Hayes responded with the Hayes Express 96 protocol, a 9600 bit/s protocol. It was sometimes referred to as the "Ping-Pong" protocol due to the way the modems could "ping-pong" the single high-speed link between the two ends on demand, in a fashion similar to the USR and Telebit protocols. The key improvement is that the channel could be switched very rapidly, without a renegotiation procedure. However, Express 96 both was late to market and lacked error correction, making it far less attractive than its competition. The design was generally unsuccessful, and for the first time Hayes lost cachet as the leader in modem design and manufacture. Hayes's slow entry into the high-speed market led to a fracturing of the command set. In order to set up the modem to accept or reject certain types of connections, Hayes had added a number of new commands prefixed by (the ampersand) to the Smartmodem 2400. Other companies offering 2400 bit/s generally followed the same syntax. When Hayes moved to the Smartmodem 9600, they extended the set further, using the same syntax. However, by this time the other companies involved had introduced their own syntax;