Fall back is a feature of a modem protocol in data communication whereby two communicating modems which experience data corruption (due to line noise, for example) can renegotiate with each other to use a lower-speed connection. Fall forward is a corresponding feature whereby two modems which have "fallen back" to a lower speed can later return to the higher speed if the connection improves.
Article based on fall back and fall forward at FOLDOC, used with permission.
