When set to True, outbound calls that are not answered by the gateway within 10 seconds will be routed to the next available trunk; if there are no additional trunks then the call will automatically be dropped. In an organization with slow networks and gateway responses, that could potentially result in calls being dropped unnecessarily.
The default value is True.
Set-CsTrunkConfiguration
-Identity "site specific trunk"
-EnableFastFailoverTimer $false"
