The calls are switched in the following steps:
- Processing the calling number (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. The entries in the call routing table consist of records of conditions and instructions. The entries 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. If an entry is found here matching the number that is called, and that also has the appropriate destination domain, then the call is delivered to the corresponding subscriber. If no local subscriber is found for whom the number and destination domain match, another pass is made where it suffices for the telephone number of the local subscriber to match the called number; the destination domain is not considered.
- Resolution of the call with default entries in the call-routing table
If the previous passes through the call routing table and the lists
with the local subscribers were unsuccessful, the call is checked again
in the call routing table. This pass only takes the default routes into
account, however. It does not include the numbers and destination domains
that were entered in the default routes. Only the source filters are
processed, assuming that the default routes has these filters.
Note: The procedure described here only considers the call numbers as processed by the Call Router. Mapping to the ISDN or SIP line can also alter the number.