A Service Control Point (SCP) has a call list associated with the main telephone number of a called party. When a calling party attempts to contact the called party by calling the main number, but cannot reach the main number, a Service Switching Point (SSP) fires a trigger. One trigger is a T_No_Answer...http://www.google.de/patents/US7711102?utm_source=gb-gplus-sharePatent US7711102 - Automatically sequentially ringing alternative telephone numbers
