This sets how long the forward signal digit stays turned off, once the backward acknowledgment has been received and the forward tone has been switched off, in compelled signaling mode. This off-period is the required settling gap between digits in compelled signaling, ensuring the far end's tone detectors have clearly seen the tone go off before the next digit's tone-on begins, which prevents digit smearing on trunks doing rapid digit exchange. If this timer is set too short, for example 20 ms, on a noisy trunk, the far end's tone detector might not register a clean off-period between digits, risking two adjacent digits being misread as one.