A voice over Internet protocol, VoIP, network comprising: an integrated Internet telephony system having an application layer gateway function, a signaling processing function and a media processing function integrated in one structure, the integrated Internet telephony system comprising: a first interface connected to a public network; a second interface connected to a private network; and a third, virtual, interface connected to a different network from the first interface and the second interface; wherein the integrated Internet telephony system is adapted to perform an application layer gateway, ALG, processing on a packet bound to a first address and process a signaling message bound to a second address and to set up a call session between an external session initiation protocol, SIP, terminal connected to the public network and an internal SIP terminal connected to the private network, and perform a media processing on a real time protocol, RTP, packet based on a third address, the RTP packet exchanged through the call session, wherein the first address is a private Internet protocol, IP, address of the second interface; the second address is in a same network as the first address, but is a different logical IP address from the first address; and the third address is in a same network as the third interface, but is a different logical IP address from the third interface. an integrated Internet telephony system having an application layer gateway function, a signaling processing function and a media processing function integrated in one structure, the integrated Internet telephony system comprising: a first interface connected to a public network; a second interface connected to a private network; and a third, virtual, interface connected to a different network from the first interface and the second interface; wherein the integrated Internet telephony system is adapted to perform an application layer gateway, ALG, processing on a packet bound to a first address and process a signaling message bound to a second address and to set up a call session between an external session initiation protocol, SIP, terminal connected to the public network and an internal SIP terminal connected to the private network, and perform a media processing on a real time protocol, RTP, packet based on a third address, the RTP packet exchanged through the call session, wherein the first address is a private Internet protocol, IP, address of the second interface; the second address is in a same network as the first address, but is a different logical IP address from the first address; and the third address is in a same network as the third interface, but is a different logical IP address from the third interface. a first interface connected to a public network; a second interface connected to a private network; and a third, virtual, interface connected to a different network from the first interface and the second interface; wherein the integrated Internet telephony system is adapted to perform an application layer gateway, ALG, processing on a packet bound to a first address and process a signaling message bound to a second address and to set up a call session between an external session initiation protocol, SIP, terminal connected to the public network and an internal SIP terminal connected to the private network, and perform a media processing on a real time protocol, RTP, packet based on a third address, the RTP packet exchanged through the call session, wherein the first address is a private Internet protocol, IP, address of the second interface; the second address is in a same network as the first address, but is a different logical IP address from the first address; and the third address is in a same network as the third interface, but is a different logical IP address from the third interface.