Abstract: In a local communication network, stations can be attached via extension lines and individual ports in distribution panels to the main transmission ring (11). Each port has a physical address or local identification key. Means are provided for inserting the local key of a port into a station when it is plugged into the extension lines. Each station comprises units (33, 45) for generating a key demand signal and an idling signal pattern which are transmitted to the port, and a key register (47) for recording the key when it is received. Each port includes a read-only store and timing unit (41) which furnishes the local key in response to the received idling pattern which is converted to a clock signal. A switch (37) in the port is activated by a switch control unit (35) to insert the read-only store and timing unit into a wrap-around loop interconnecting input and output paths of the station.