Call-by-Call Service Selection provides special incoming call-handling treatment for ISDN and SIP trunk groups. The system handles an incoming call on an ISDN or SIP trunk according to a treatment table that you administer for the trunk group. Depending on the platform that you use, a different number of combinations of call treatments are possible in the treatment table.

The system selects the treatment for an incoming call based on the first three columns of the Incoming Call-Handling Treatment (ICHT) screen. When the attributes of an incoming call match these specifications, the system treats the call according to the corresponding entries in the next four columns of the table. If an incoming call matches more than one set of specifications, the most restrictive case applies. The following table lists the possible cases from most restrictive to least restrictive.