EXTENSION SYSTEM, EXTENSION SERVER, AND COMMUNICATION METHOD

摘要

A private branch exchange system capable of enabling radio communication terminals belonging to an extension group to perform device-to-device direct communication (D2D communication) by using a radio access network such as LTE. A private branch exchange server 300 includes a transition trigger detection unit 310 configured to detect a trigger for a transition to the direct communication, an extension group list retention unit 320 configured to retain an extension group list containing an identifier of the radio communication terminal belonging to the extension group, a subgroup selection unit 330 configured to select a certain subgroup from the extension group list, and a direct communication command unit 340 configured to send permission information on the direct communication and configuration information on a communication environment necessary for the direct communication to the radio communication terminal contained in the subgroup selected by the subgroup selection unit 330.