Hamy,
1. The Quintum Tenor should only re-route to the PSTN when IP calls fail for the following cause codes 3, 31, 34, 38, 41-45, & 47. It will also re-route on code 17 if partial trunk group is enabled.
2. This is an issue where you have not setup the answer supervision correctly. In the PSTN trunk group , set supervision to 2 (answer) or 3 (answer & disconnect), set the answerdelay to 120 and make sure progtone is set to 0. For more information on this review the answer supervision document on Quintum’s web site at;
http://www.quintum.com/support/1G/kb/telco/Answer_Supervision.pdf