Communication network system, calling terminal and voice call establishing method thereof

摘要

A communication network system, a calling terminal and a voice call establishing method thereof are provided. The communication network system comprises a called terminal, the calling terminal and a session initiation protocol (SIP) server. The calling terminal generates and transmits an invite message including IPv4 connection information and IPv6 connection information of the calling terminal. The SIP server is communicatively connected to the calling terminal and the called terminal. The SIP server receives the invite message from the calling terminal and forwards the invite message to the called terminal. The called terminal establishes a voice call with the calling terminal according to one of the IPv4 connection information and the IPv6 connection information of the calling terminal.