Patent ID: 8572259

Claim:
A data communication terminal that performs data communication with a communication destination device through a proxy device in a data communication network, using a predetermined transport layer protocol, the data communication terminal comprising: circuitry configured to: transmit an address request to the proxy device using an application layer protocol, to get global address information which is used when establishing a connection with the communication destination device by the predetermined transport layer protocol, the application layer protocol being set to be usable in advance between the proxy device and the data communication terminal; establish a connection with the proxy device by the predetermined transport layer protocol; transmit connection destination information of the communication destination device to the proxy device using the application layer protocol, to request for a connection by the predetermined transport layer protocol between the proxy device and the communication destination device; and transmit data over a communication channel connected by establishment of the connection with the proxy device by the predetermined transport layer protocol and connection by the predetermined transport layer protocol between the proxy device and the communication destination device by embedding the global address information, as a source address, in the data of the application layer when using Session Initiation Protocol (SIP).