Patent ID: 7545821

Claim:
A network system, comprising: a plurality of communication devices which can communicate with each other; an address translation device having a table to translate a global address and a private address into each other, the address translation device assigns port information to the private address to be used and relays data transmission between the communication devices; and a port information transmitting device connected between the address translation device and an external network to transmit the port information assigned by the address translation device, wherein one of the plurality of said communication devices comprises: means for sending a pseudo-packet containing an address of another communication device and predetermined information, before sending information to another communication device, to the port information transmitting device via the address translation device, the address translation device comprises: means for assigning new port information to a pseudo-packet address of one of the communication devices, and means for sending the address of one of the communication devices and the assigned port information to the port information transmitting device, wherein the port information transmitting device comprises: determining means for determining whether a received communication packet contains the predetermined information; and means for sending the port information corresponding to the received address of one of the communication devices in case that said determining means determines that the predetermined information is contained, one of the communication devices further comprises: means for sending the received address of one of the communication devices and the assigned port information to another communication device, and another communication device further comprises: means for transmitting information with one of the communication devices using the received address of one of the communication devices and the assigned port information.