This sets how long the forward digit tone stays on, once turned on, while waiting for the corresponding backward signal in compelled R2 signaling. Compelled signaling specifically requires each forward tone to hold until acknowledged before the next digit can be sent, so this timer's value directly paces how fast digit-by-digit call setup can proceed on this trunk; too short and legitimate backward responses get missed, too long and setup is needlessly slowed. With this set to 1 second, the gateway holds each forward digit tone on the line for up to a second waiting for the backward acknowledgment before deciding to retry or fail that digit.