A terminal (A) sends a call request message to a terminal (b). This message contains a request for a TCP/IP service. A call control section in a switching node passes the message to an agent, which, in turn, examines whether or not an IP address and a TCP port number set in the received call request message have been entered into a firewall table. If they are found, the request for access to the terminal (b) is granted. As a result, an ATM connection is set up between the terminal (A) and the terminal (b) and a TCP/IP connection is set up on the ATM connection. If they are not found, access to the terminal (b) is refused and no ATM connection is set up between the terminal (A) and the terminal (b).