Communication terminal apparatus and data transmission method

摘要

A communication terminal apparatus whereby data communication and service switching can be performed taking security into consideration, and without an application performing complex circuit connection control. In this apparatus, port number checker 260 refers to port number DB 270 and checks whether a port number included in user information transmitted from application 100 is an appropriate one. Port number DB 270 memorizes destination port numbers and communication protocols in correspondence. Port number DB 270 memorizes only those appropriate port numbers that application 100 is allowed for use and the corresponding communication protocols. U-plane monitor 280 monitors all ports of TCP/IP, detects transmission of user information from application 100, and reports a port number included in the header to port number checker 260.