 A single additional channel in the reverse direction allowed the two modems to communicate how much data was waiting at either end of the link, and the modems could change direction on the fly.The Trailblazer modems also supported a feature that allowed them to spoof the UUCP "g" protocol, commonly used on Unix systems to send e-mail, and thereby speed UUCP up by a tremendous amount.Trailblazers thus became extremely common on Unix systems, and maintained their dominance in this market well into the 1990s.