| 摘要 |
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 trigger, which is fired in response to a call to the main number that is not answered within a predefined number of rings. Another trigger is a T_Busy trigger that is fired in response to a call to the main number that is made when the main number is busy. Each trigger causes the SCP to access the call list and to cause the SSP to ring an alternative telephone number associated with the main telephone number. If this attempt to reach the called party also fails, then the SSP again fires the trigger and an attempt is made to connect the calling party to the next number on the call list. If the call list is exhausted before the calling party is connected to a number on the called party's call list, then a message can be played to the calling party. Alternatively, the calling party may be connected to a voice mailbox associated with the called party or may receive a busy tone.
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