Multi-port lan switch for a token-ring network

Each gateway of a network data unit comprises a second contact, a first gate contact, a transmitter level and a receiver level, and a switching system for switching the first gate contact in the first mode to the first mode or a second mode in accordance with the corresponding operating mode signal, the second switching contact being connected to the receiver stage, and in the second mode, the switching system connects the first gate contact with an input stage and the second gate contact to the transmitter stage. The data transmission system having a plurality of adapter cards (24, 36, 37, 42, 43), and a ring line network with at least one connection centerer (14, 44) comprises a single data transmission unit as defined above, the adapter cards (24, 36, 37, 42, 43) a concentrator (14, 44) is connected to each other's door. ŕ