The Call Manager has the central task of allocating the calls waiting to be switched to a certain line or to a certain user. The Call Manager makes this allocation by using the call-routing table and the list of registered users. The calls are switched in the following steps:
- Processing of called numbers (Calling Party ID) First of all there is a check to see whether a numeric or alphanumeric number is available. Typical dialing separators such as "()-/" and <blank> are removed. A leading "+" is left in place. In this case, the number is still treated as a numeric number. If the check reveals any other alphanumerical character, the number is treated as alphanumeric and remains unchanged.
- Resolving the call in the call routing table After processing the Called Party ID, the call is passed over to the call-routing table. Entries in the call-routing table consist of sets of conditions and instructions. The entries—with the exception of the default routes—are searched through and the first one that satisfies all of the conditions is executed.
- Resolution of the call with tables of local subscribers If no entry is found in the call-routing table, then the Call Manager searches through the list of local subscribers. Call routing considers all of the users known to the call router (registered SIP users, configured ISDN users). If an entry is found that agrees with the called number and that has the matching destination domain, then the call is delivered to the corresponding subscriber. If there is no local subscriber with matching number and destination domain, then the following cycle searches for an agreement between the number of the local subscriber and the called number; the destination domain is ignored.
- Resolution of the call with default entries in the call-routing table
If the preceding cycles referring to the call-routing table and lists
of local subscribers remain unsuccessful, then the waiting call is checked
once again with the call-routing table. This pass only takes the default
routes into account, however. The numbers and destination domains entered
into the default routes are ignored. Only the source filters are processed,
assuming that the default routes has these filters.
Note: Specific examples of call-routing procedures can be found in the configuration examples described.