In this example, a branch office network will be connected to the headquarters network over VPN. In addition to data transfer, the telephone structure in the branch office is also connected to the central SIP PBX. A LANCOM VoIP Router is used in the branch office network and a LANCOM VPN router, for example, could act as the VPN end point at the headquarters. The telephony subscribers at the headquarters receive internal extensions from the number range '101' to '199'; for each of the branch offices, a 10-digit block from the 200 range is reserved - in this example, '211' to '219'.