The configuration options for the call router offer numerous options for manipulating the telephone numbers that are used to establish the connection. The call router usually connects different "telephone worlds" (internal and external, SIP and ISDN) that use completely different telephone number ranges. So that the subscribers can communicate successfully with each other, the telephone numbers at the interfaces have to be configured in such a way that, on the one hand, the required subscriber is reached via the correct line and, on the other hand, a return call (automatically upon "engaged", where applicable) can be placed successfully. To enable this return call, the calling number (calling party ID) has to be after the processing by the Call Manager, directly before it is delivered to the relevant subscriber.