A controller (GK) of a communication system (SYS) including in each of a plurality of geographically distant zones (ZA, ZB, ZC) a zone-specific controller (GK) and one or more subscriber terminals (EP) comprises a controller characteristics memory (CCM) for storing at least a private network identifier (PNID), a private network configuration memory (PNCM) for storing the private network configuration, a private network configuration determing means (PMDM) for communicating with other controllers (GK) of the communication system to determine the private network configuration and a call router for routing a call setup message received from a subscriber terminal (EP-A.sub.3) in one zone (ZA) to another subscriber terminal (EP-B.sub.2) of another zone (ZB). Before setting-up a call or at repeated time intervals the private network configuration including the controllers and subscriber stations in all zones (ZA, ZB, ZC) which belong to the private network identified by the private network identifier (PNID) can be determined and this private network configuration is used for determining the location of the respective controller which serves the called subscriber station (EP-B.sub.2).