| 摘要 |
PROBLEM TO BE SOLVED: To provide a communication system which is capable of maintaining two-way communication between a computer in a LAN and another computer located outside a LAN without hindrance and the computers used in the system. SOLUTION: In a two-way data transmitting-receiving system through a communication network, a computer located in a LAN and another computer located outside a LAN are connected together through a communication network, and data signals accompanied by a port number are sent to an address, so that a transmitting end and a receiving end are specified. The LAN is equipped with a fire wall and has a function of changing the port number of data signals sent from outside the LAN to the inside of the LAN and vice versa under the prescribed conditions. The LAN has another function of finding out the former port number of a receiving end so as to enable the fire wall to allow the data signals accompanied by the current port number of the receiving end to pass when a computer located outside the LAN transmits data signals accompanied by the port number of a receiving end to a computer located inside the LAN.
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