A client device comprises a connection destination register that transmits a client identifier to an address management device via a first node; a UDP controller that controls a UDP connection upon reception of a TCP connect from an application executer, and a TCP-session controller that establishes, between itself and the application executer, a first TCP connection identified by a connection identifier. A server device comprises a connection destination register that transmits a server identifier to the address management device via a second node; a UDP controller that controls a UDI connection; and a TCP session controller that establishes, between itself and a service provider, a second TCP connection identified by a connection identifier. A UDP connection via the first node and second node can be established between a communication serve processor and a communication client processor.