Abstract: The present invention relates to data communication networks. In particular, the present invention relates to a procedure and a system for ensuring emergency communication in a data communication network in which the terminal devices (4a, 4a, 4c) are connected to a telephone exchange (1) via an access node (3) consistent with the V5 standard. In the procedure of the invention, emergency communication by a subscriber in the event of a failure of the V5 interface used by the subscriber is ensured by using an emergency V5 interface (6) created in the access node and a reange of addresses created for this purpose in the telephone exchange.