PURPOSE: To execute communication having a high quality by constituting the titled device so that each exchange collects signals from packet terminals at every route between the exchanges and executing unitarily a data link control.

CONSTITUTION: For instance, when a user packet from a terminal 101 and a user packet from a terminal 103 are addressed to a terminal 301 and a terminal 303 respectively, both of them are packets addressed for an exchange node 3, therefore, a link control is executed unitarily. Concretely as for inter-station packets with respect to the user packets from the terminals 101 and 103, the same inter-station addresses DNA, SNA are provided, and a control for continuing a transmission sequence number, as well, in a control filter C is executed. That is to say, the link control is executed in a lump by communication between the exchange nodes without being conscious of a transmission terminal. A link control circuit 79 further analyzes the inter-station packet from the other exchange node received in a buffer 71, and executes an error retransmission control, a flow control, etc. Also, the inter-station packet received normally is formed to a user packet (a) by removing the header of its inter-station communication, thereafter, sending the packet to a bus 91.