This read-write Integer32, ranging from 250 to 10000 milliseconds in 250ms increments (default 1000ms), sets how long the gateway waits after sending an NSE 200 for the NSE 201 acknowledgement or NSE 202 negative acknowledgement before assuming the far end rejected or discarded the request to switch to T.38 fax. An admin cares because too short a timer can abandon a legitimate T.38 switch-over before the far end responds, dropping back to voice-mode fax transport unnecessarily. For example, on a network with higher latency, an admin might increase this timer from the 1000ms default to reduce false T.38 switch-over failures.