fall back

retreat, recede; fail to keep a promise

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.
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Verb
1. fall backwards and down
(hypernym) lean back, recline
2. hang (back) or fall (behind) in movement, progress, development, etc.
(synonym) lag, dawdle, fall behind
(hypernym) follow
(hyponym) drag, trail, get behind, hang back, drop behind
3. move back and away from; "The enemy fell back"
(synonym) recede, retire
(hypernym) withdraw, retreat, pull away, draw back, recede, pull back, retire, move back
(hyponym) ebb, ebb away, ebb down, ebb out, ebb off
(derivation) disengagement, fallback, pullout
4. retreat
(synonym) lose, drop off, fall behind, recede
(antonym) gain, advance, win, pull ahead, make headway, get ahead, gain ground
(hypernym) regress, retrograde, retrogress
5. have recourse to; "The government resorted to rationing meat"
(synonym) resort, recur
(hypernym) use, utilize, utilise, apply, employ
6. go back to bad behavior; "Those who recidivate are often minor criminals"
(synonym) relapse, lapse, recidivate, regress, retrogress
(hypernym) revert, return, retrovert, regress, turn back

A feature of a modem protocol where two modems which experience data corruption, e.g. due to line noise, can renegotiate to use a lower speed connection. See also fall forward.

move back, go back The runner fell back from the rest of the runners when the race was half over.