slotted ring
With the slotted ring, the time axis is divided into time slices (slots) of fixed length. The slots then correspond to circulating message containers.
A status indicator is assigned to each slot, indicating whether the slot is currently free or occupied. Messages can be inserted into free slots by stations willing to transmit. Either the station empties the slot when its own messages are received back and may immediately insert new messages on this occasion, or it empties the slot after receiving back, but may then not transmit again immediately, but passes on the right to transmit indirectly to the following station.
The first version is only feasible if there are more slots than stations. This is because a station is able to monopolize a slot for itself. Thus, with fewer slots than stations, some stations can be permanently excluded from traffic.
The second version corresponds to an indirect token procedure and, like it, guarantees access to the transmission medium for all stations in a fair manner. The disadvantage is that in borderline situations, only every second slot can be used for transmission in the second version, whereas every slot can be used in the first version. The border situation occurs exactly when one station transmits everything and the others are only receivers.