This Integer32 (0..3600), in seconds, sets how long the local ring-back tone toward the TDM side is generated unless interrupted by an answer or delete-connection command, with zero meaning indefinite; it requires a non-NULL tone plan. This gives the caller on the TDM side audible feedback that their call is proceeding, and an admin caps its duration to avoid an indefinite tone if the far end never answers or the call is never torn down properly. For example, if calls that go unanswered are found stuck generating ring-back tone indefinitely, an admin would set vismDsx1RingBackTO to a finite value to cap that behavior.