CLOSED USER GROUP FACILITY

摘要

A closed user group facility in a data transmission system which has a closed user group of terminals accomodated in a switching network and inwhichh the switching network registers a terminating terminal in response to a request for registration of that designated terminating terminal from another one of the terminals. The registration of the Corresponding terminating terminal is with one of codes with which all the terminals accomodated in the switching network can be individually identified. Subsequently when transmitting data (including voice data) from the transmitting terminal to the terminating one , the switching network controls to permit the transmission of the data from the transmitting terminal to the terminating one when the switching network has verified that the transmitting and terminating terminals had already been mutually registered as distant terminals